Patient Protection and Education for Students

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Unit 1
Introduction to Radiation Protection
Sect. 1.1: History of radiation protection
Sect. 1.2: Justification of radiation exposure
Sect. 1.3: Optimization of radiation exposure
Sect. 1.4: Patient protection and education
Sect. 1.5: Radiation and radiation sources
Sect. 1.6: Medical radiation exposure
Sect. 1.7: Interaction of x-radiation with matter
Section 1.1
Discovery of X-Rays
•November 8, 1895 by Wilhelm Conrad Roentgen a German physicist
–Working in his darkened laboratory investigating fluorescence with a Crookes tube which was enclosed  in black photography paper
–Noticed a plate coated with barium platinocyanide several feet away was glowing
–Placed various materials between the Crookes tube and the fluorescing plate
–He called the rays “x” Rays, “x” for unknown
–Presented his findings to the scientific community in December 1895
–In 1901 won the first Nobel Prize in Physics
•First x-ray was of his wife’s hand in early 1896
First Reports of Injury
•In the early as 1900s injuries were being observed
–Skin damage (radiodermatitis)
–Loss of hair (epilation)
•In 1904 the first x-ray fatality was reported in the USA, Clarence Madison Dally
•Blood disorders (anemia, leukemia) were being occurring at a higher rate in radiologists
Reducing Radiation Exposure
•Due to the biological damage observed in x-ray pioneers, protective devices were developed
–Lead aprons and gloves
–Personnel radiation monitoring devices
–Advances in technology permit lower doses to acquire x-rays

Section 1.2
•Benefit vs. Risk
•The referring physician has the responsibility to conduct  a thorough clinical examination to ensure the benefits of the ordering an x-ray outweigh  the potential risk of biologic damage
Guidelines for the Prescription of X-ray Examinations
•“Unnecessary radiation exposure of patients can be significantly reduced by ensuring that all examinations are clinically justified.”
1. The prescription of an x-ray examination of a patient should be based on clinical evaluation of the patient and should be for the purpose of obtaining diagnostic information or patient treatment
2.“X-ray examinations should not be performed if there has been no prior clinical examination of the patient.”
3. “Radiological screening must not be performed unless, it has been proven that the benefit to the individual examined or the population as a whole is sufficient enough to warrant  its use.”
SC35 Section A: Responsibilities and Protection; 3.1 Guidelines for the Prescription of X-ray Examinations; P. 12
4. It should be determined whether there have been any previous x-ray examinations which would make further examination unnecessary, or allow for the ordering of an abbreviated  examination. Relevant  previous images or reports should be examined along with a clinical evaluation of the patient.
5. When a patient is transferred from one physician or hospital to another any relevant images, or reports should accompany the patient and should be reviewed by the consulting physician
6.When prescribing a radiological examination, the physician should specify precisely the clinical indications and information required.
SC35 Section A: Responsibilities and Protection; 3.1 Guidelines for the Prescription of X-ray Examinations; P. 12

CAMRT: Risk Management Guidelines
•Patient related –general (PRG) Annex  C: Requisition / Requests for Consultation
•No radiographic or imaging examination should be performed by a technologist without:
–A formal request in writing from an authorized referring physician;
–A requisition signed by a person authorized by the facility to order treatment and/or diagnostic examinations; etc.
•Staff related –general (SRG) Annex B: Qualifications and Scope of Practice
–It is recommended that in each facility the following are prominently  displayed
•CAMRT Code of Ethics
•Scope of Practice for the Profession(s)
–These guidelines are recommended as a way to inform the public of the profession and the profession’s standards, ethics, and limitations. Etc.
Section 1.3
Optimization of Radiation Exposure
•As Low As Reasonably Achievable and As Low As Reasonably Practicable
•This concept encourages strategies to minimize dose to an individual by performing only the required x-rays, using appropriate  exposure factors for the body part of interest, ensuring only the area of interest is within the collimated field, etc.

Section 1.4
Effective Communication
•Educate the patient about the procedure they are scheduled to have
•Your expectations of the patient during the procedure
•Provide follow-up instructions
•Effective communication contributes to a positive experience for the patient
Risk of proceeding  with the Examination
•Radiation sciences consider risk as the “possibility of inducing a radiogenic cancer or genetic defect after irradiation”
•Informed patients will understand and agree to proceeding with an examination (the benefit) to help determine what is ailing  them
•A great deal of knowledge has been gained to better understand biologic effects from medical x-ray exposure
•Advances in equipment design and safety standards reduce the risk of imaging procedures

•Background Equivalent Radiation Time
•A technique that may be used by a technologist to help relay  the concept of “risk” to their patient
•A unit of time (days, weeks, months, years) that is assigned to certain radiographic examinations representing the length of time that would be required to obtain a comparable dose from natural sources
–CXR -BERT = 10 days

Section 1.5
Radiation and radiation sources
What is Radiation?
•Energy in transit from one location to another
1. Mechanical vibrations
2. Electromagnetic radiation (EMR)
•Characterized by wavelength
•Higher frequency associated with shorter wavelength and higher energy
•Information Sheet 1.3

1. Ionizing radiation (EMR, particulate)
–X-rays, γ rays, α particles, β particles
–Sufficient kinetic energy to eject an electron from the atom
–Foundation of interaction of x-rays with human tissue
2. Non-ionizing radiation
–Ultraviolet, visible light, infrared, microwaves, radio waves
Sources of Radiation
1. Natural radiation
2. Manmade or artificial radiation

Natural radiation
1. Terrestrial radiation
–Radioactive elements present in crust  of the earth (1.98 mSv/year in the U.S.)
2. Cosmic radiation
–Results from nuclear interactions in sun & other stars (0.3 mSv/year in the U.S.)
3.Internal radiation
–Tissues of human body contain many naturally existing radionuclides(0.67 mSv/year in the U.S.)
•Total: 2.95 mSv/year in the U.S.
Manmade or artificial radiation
1. Consumer products containing radioactive material
2. Air travel (0.005 –0.01 mSv/hour)
3. Nuclear power plants
4. Atmospheric fallout  from Nuclear Weapons
5.Nuclear power plant accidents
6.Medical radiation

Nuclear Power Plant Accidents
•Three Mile Island –March 28, 1979
–Pressurized  water reactor overheated causing overheating of the radioactive core
–About 40% of the reactor core reached the molten state settling on the bottom of the reactor vessel
–Fortunately there was no “melt-through” resulting in only a small quantity of radiation escaping
–No health problems to occupational workers or the 2 million people living within 50 miles of the plant
•Chernobyl –April 26, 1986
–An explosion releasing radioactive nuclides, more than 1 million times the amount released at TMI
–200 workers received whole body doses exceeding 1 Sv
–More than 2 dozen workers received doses greater than 4 Sv
–Average dose received by quarter of a million people within a 200 mile radius was 0.2 Sv
•Fukushima 1 –March 11, 2011
–Japan experienced an earthquake measuring 9.0 on the Richter scale which triggered a tsunami
–The tsunami reached the reactors and disabled the reactors cooling system; an explosion left the reactor cores bare  increasing the nuclear radiation levels in the surrounding areas
–On April 20, 2011 Japanese authorities declared the 20 Km evacuation zone be entered only under government supervision

Section 1.6
Medical Radiation
•Diagnostic imaging and nuclear medicine
•Natural radiation exposure is relatively constant, however medical radiation exposure is increasing
–Medico-legal considerations
–Physicians relying more on radiologic diagnosis to assist in patient care
–According to SC35 the use of X-rays (dental & medical radiography) accounts for > 90% of total man-made radiation dose to the population

New Data on Medical Radiation Exposure
•The number of medical procedures involving radiation has increased since the 1980s
–1987: Manmade 18% [Figure 1-8]
–2006: Manmade 48% [Figure 1-9]
•The main reason for this increase is the use of CT
–1980: CT collective dose of 3700 person-Sv
–2006: CT collective dose of 440,000 person-Sv
Section 1.7
Interaction of x-radiation with matter
Potential Biological Damage
•The majority of x-rays that pass through the body are attenuated
•Attenuation is a reduction in the number of primary photons through absorption and scatter as the beam passes through the patient
•Energy that is transferred to the tissues may result in ionization or excitation at the atomic level with the final outcome of potential biological damage
Information Sheet 1.1

Exposure Factor Selection
•The MRT determines and selects the appropriate exposure factors;
–kVp determines the energy of the x-ray beam
–mA determines the quantity of x-rays produced
–Time determines the length of time x-rays are emitted from the x-ray tube / the length of the exposure
•Selected exposure factors determine patient dose

X-ray Interaction with Matter
•In the diagnostic range two interactions with matter are predominant
–Photoelectric absorption
–Compton scattering
•The predominance  of both interactions depends on the incident photon energy
–As photon energy increases the predominant interaction is Compton scattering
–Most interactions occur within the first 5 cm of tissue

Photoelectric Absorption
•Involves the complete absorption of the incident x-ray photon by tissues
•Therefore is the major contributing factor to patient dose

Compton Scattering
•Involves partial energy of the incident x-ray photon is transferred to the tissues
•The x-ray photon is deflected  and is now referred to as a scattered photon
•The scattered photon continues to move through tissue along a new path and at a lower energy
•The scattered photon may scatter several more times before being completely absorbed

Unit 2
Concepts of Radiation Protection
•Sect. 2.1: Radiation quantities and units
•Sect. 2.2: Personnel monitoring
•Sect. 2.3: Radiation detection and measurement
•Sect. 2.4: Radiation protection organizations
•Sect. 2.5: Radiation-induced responses and goals of radiation protection
•Sect. 2.6: Radiation exposure risk and dose limits
Section 2.1
Radiation quantities and units

1 Gy = 100 rad
1 rad = 0.01 Gy = 10 mGy
20 mSv = 2 rem
150 mSv = 15 rem
5 mSv = 500 mrem
1 mSv = 100 mrem
3 Gy = 300 rad
0.2 mGy = 20 mrad
0.1 Gy = 10 rad

Radiation Units
Traditional Units
1. Roentgen (R)  exposure
2. rad(rad)  absorbed dose
3. rem(rem)  equivalent & effective dose
4. Curie (Ci)
SI Units
1. Air kerma (Gy or Gya)  exposure
2. Gray (Gy or Gyt)  absorbed dose
3. seivert (Sv)  equivalent & effective dose
4. Becquerel (Bq)
SI Units
•Le Système International d’Unités
•International System of Unit
–Adopted in 1960
–Extension of the metric system
–All branches of radiation science
•SI units and traditional units are in use today.
•The total electrical charge per unit mass that x-ray photons with energies up to 3MeV generate in dry air at standard temperature and pressure
•Precise measurement of radiation exposure requires a device called an ionization chamber
•Traditional unit: Roentgen (R)
•SI Unit: Air kerma expressed in gray (Gy or Gya)
•Relationship: 1 Gy ~ 115 R
1 R = 1 Gy divided by 115 R
= 0.008695 Gy OR 8.695 mGy
(SC35 ~8.73 mGy)
Absorbed Dose (D)
•The amount of energy absorbed per unit mass of the medium
•Absorbed energy is responsible for any biologic damage
–Amount of energy absorbed depends on the atomic number (Z) and mass density of the tissue (kg/m3)and the energy of the incident photon (keV)
Unit of Absorbed Dose
•Traditional unit: rad (radiation absorbed dose)
–1 rad= 100 ergs/g
•SI Unit: Gray (Gy or Gyt)
–1 Gy= 1 J/kg
•Relationship: 1 Gy= 100 rad
1 rad= 1 Gy divided by 100 rad
= 0.01 Gy OR 10 mGy

Dose Equivalence
•Takes into consideration that different types of radiation, in equal absorbed doses, cause different amounts of biologic damage
•A quality factor (Q) is used to adjust  the absorbed dose value

Radiation Weighting  Factor (WR)
•Chosen for each type and energy of radiation
•Selected by national and international scientific advisory  bodies (NRCP, ICRP )
•Important in radiation protection
Equivalent Dose (EqD)
•Product of average absorbed dose in Gy (D) and its radiation weighting factor (WR)
EqD= D x WR
Unit of Equivalent Dose
•Traditional unit: rem(radiation equivalent man)
•SI unit: Sieverts(Sv)
1 Sv= 100 rem
1 rem= 1 Svdivided by 100 rem
= 0.01 SvOR 10 mSv
Calculating Equivalent Dose
EqD= D x WR
(Sv) = (Gy) x WR
Read and study examples on P. 65 Statkiewicz Sherer

Tissue Weighting Factor (WT)
•Takes into account the overall harm to each organ and tissue
•Measure of relative risk associated with irradiation of different tissues
Effective Dose (EfD)
•Provides an overall risk of exposure to ionizing radiation
•Incorporates  the effect of the type of radiation used (WR), and radiosensitivity of the organ or part irradiated (WT)

Unit of Effective Dose
•Traditional unit: rem (radiation equivalent man)
•SI unit: Sieverts (Sv)
1 Sv= 100 rem
1 rem= 1 Svdivided by 100 rem
= 0.01 SvOR 10 mSv

Calculating Effective Dose
EfD= D x WR x WT
(Sv) = (Gy) x WR x WT
Read and study examples on P. 66 Statkiewicz Sherer
Read and study Table 3-4 on P. 67 Statkiewicz Sherer

Diagnostic Radiology
•X-rays are used to acquire images in diagnostic radiology therefore…
1R = 1 rad= 1 rem
1 Gya= 1 Gyt= 1 Sv

Collective Effective Dose (ColEfD)
•Radiation exposure to a population or group from low doses of radiation
•Product of average effective dose of an individual belonging to the exposed population and number of persons exposed
•Traditional Unit: man-rem
•SI Unit: person-sievert
Read and study example on P. 67 Statkiewicz Sherer
Radiation Units
Table 3-5: SI and Traditional Unit Equivalents
P. 67 Statkiewicz Sherer
Table 3-6: Summary of Radiation Quantities and Units
P. 68 Statkiewicz Sherer

Section 2.2
Personnel monitoring
Personnel Dosimetry
•Refers to monitoring of individuals who are exposed to occupational radiation
–All operators of X-ray equipment
–Personnel routinely participating in radiological procedures
•Monitoring is necessary for anyone who may receive 1/20thof annual dose limit
(SC35 P. 10: 2.1.6 )
•Personnel monitoring devices are worn to ensure:
–Workers receive doses below the stated dose limits in SC35
–To monitor radiation safety practices
–Lightweight and easy to carry
–Durable, ability to withstand normal daily use
–Ability to detect both small and large doses consistently  and reliably
–Withstand  sensible  amount of heat, humidity, and pressure
–Reasonably inexpensive to purchase and maintain

Wearing the personnel dosimeter
•Radiography (no protective lead apron worn)
1. on trunk of body at level of waist , on anterior surface of the individual
2.Upper chest region at level of collar area, on anterior surface of the individual
•Fluoroscopy (protective lead apron worn)
– Must be worn under the apron
–“If extremities  are likely to be exposed to significantly higher doses, additional dosimeters shouldbe worn at those locations on the body.” (SC35 P. 10: 2.1.7)

Types of personnel dosimeters that detect ionizing radiation
–Film badge
–Optically stimulated luminescent (OSL)
–Pocket ionization chamber
–Thermo luminescent dosimeter (TLD)

Film Badge
•Have been in use since the 1940s
•Consist of a small case with a piece of film placed between filters
–Filter material is usually aluminum and copper
–Allow estimation of the photon energy
–Filter shapes may be different in the front of the film back compared to the back of the film badge
•Uses special radiation dosimetryfilm that is predominantly sensitive to x-rays
•Based of the photographic effect; the ability of radiation to blacken photographic film
•The film is processed and the optical densities are read with a densitometer
•Radiation dose may be measured using a dose-density curve
–A dose-density curve is obtained by exposing  a number of different films to known doses of radiation

Control Badge
•Included with each batch  of film badges
•Stored in a non-ionizing area in the facility
–The optical density reading should indicate only a base plus fog (B+F) measurement
•Serves as a basis to compare the optical density readings from other badges
–Ensures false readings are not recorded

Advantages of Film Badges
•Inexpensive, easy to use and easy to process
•Mechanical integrity
•Able to differentiate between primary beam and scatter radiation exposure
•Provide a permanent record of personnel exposure

Disadvantages of Film Badges
•Are able to detect at or above 0.1 mSv(10 mrem)
–Are not sensitive to lower levels of radiation
•Susceptible  to fogging caused by high temperatures and humidity
–Limited wearing period of one month
•Time required to process and compare to standard test film

Review of Energy levels
•Valence band
–Electrons are loosely bound and are free for sharing by adjacent atoms or molecules
•Conduction  band
–Electrons within this band are free to move providing they maintain a certain  minimum energy
–If the electrons fall below the minimum, they return to the valence band or other vacant electron site
•Carlton and Adler
–Figure 3-10 P. 48
•Position of the valence band and conduction band
•Forbidden band or gap
–Electrons may pass through this gap if they are energetic enough, but cannot exist within this area
•When energy is absorbed by the electrons in the radiation monitors, they [the electrons] get trapped in the forbidden band and reside there until their energy level is increased allowing them to move into the conduction band

OSL Dosimeter
•Developed in the late 1990s
•A plastic blister pack enclosing an aluminum oxide (Al2O3) strip sandwiched within a filter pack  that is sealed within a light-tight black paper wrapper
–Filter material is aluminum, tin  and copper
–Enables radiation energy discrimination
•Uses aluminum oxide (Al2O3) as the radiation detector
•Irradiation of Al2O3→ some electrons are stimulated into an “excited” state and are trapped in the forbidden gap or band
•Processing involves laser  illumination → stimulates electrons and increases there energy state therefore moving them temporarily into a higher energy level; the conduction band
•The electrons fall back into the “vacant  electron site” they had previously occupied and the loss of energy causes emission of light proportional to dose received

Advantages of OSL Dosimeters
•Ability to detect a dose of 0.01 mSv(1 mrem)
•Reanalysis to confirm the dose
•Qualitative information about the exposure
•Ability to read energies from 5 keV to >  40 MeV
•May be worn for a period of one year
–Common practice; 2 month wearing period

Disadvantage of OSL Dosimeters
•OSL dosimeters are shipped to the monitor company for processing therefore do not provide immediate dose results

Pocket Dosimeter
•Resembles a large pen
•Contains an ionization chamber with an eyepiece  at one end and a charging rod at the other end
–Ionization chamber contains two electrodes/fibres; one fixed and the other movable
–The movable fibre can be seen through the transparent scale  (reading scale) of the eyepiece
•Special charging unit
–The pocket dosimeter is charged to a predetermined  voltage so the quartz fibre indicates a zero reading
•The pocket dosimeter is charged causing the moveable quartz fibre to repel  the fixed central electrode/fibre
•Exposure to radiation causes ionizations within the chamber
•The ionizations cause the moveable fibre to move closer to the fixed fibre
•The scale is read through the eyepiece providing an estimated  X-ray dose

Advantages of Pocket Dosimeter
•Provides an immediate exposure reading
•Compact, easy to carry and convenient to use
–High-exposure areas i.e. cardiac catheterization procedures
•Easily recharged and reused
•Reasonably accurate and sensitive
–Sensitivity ranges from 0 to 200 mR
Disadvantages of Pocket Dosimeters
•Expensive ~ $150.00 per unit
•If not read on a timely basis may result in an inaccurate reading
•Mechanical shock may lead to false high readings
•No permanent legal record of personnel exposure

•Appearance similar to a film dosimeter
•Contains a holder and an insert
•Insert consists of an aluminum plaque , lithium fluoride chips/powder and an identification number
–Lithium fluoride (LiF) is the radiation sensing material
–TLD chips are usually 3 mm x 3 mm x 1 mm thick
•Requires a TLD analyzer for measuring the dose received to the TLD badge
•The TLD absorbs energy when exposed to x-rays and stores the energy in an “excited” higher state; the number of electrons that become trapped is proportional to the absorbed dose
•To measure the dose the plaque containing the LiFcrystals is placed in the TLD analyzer and exposed to increasing temperatures
•The heat frees the “trapped” electrons and alters  the state of the crystal structure causing the electron to return to the valance band → light is released in the proportion to the amount of radiation absorbed
•The amount of light released (luminescence) is measured with a photomultiplier tube or a photodiode
•The intensity of light is plotted  on a glow curve
•The parameters are measured and converted to a dose

Advantages of TLDs
•LiFcrystals interact with ionizing radiation similar to soft tissue
–The Z of LiFis equal to 8.2; Z of soft tissue is 7.4
•Exposures as low as 0.05 Gyt (5 mrad) can be measured
•Withstand  certain amount of heat, humidity, and pressure
•Can be worn for 3 months
•Crystals are reusable as the heating process restores the crystal to its original condition
•TLD responds proportionally to dose; if the dose is doubled the TLD response is doubled
•Instantaneous  readings are possible if a department has a TLD analyzer
•TLD monitors are also used to measure patient dose
–There small size and various configurations allow them to monitor doses in a small area such as a body cavity

Disadvantages of TLDs
•High cost
•Generally are sent to a facility for analysis of dosimeter results
•Can only be read once, readout  process destroys the stored information
•TLD crystals that are energy dependent need to be calibrated to the appropriate energy level they will be measuring
•TLDs do not respond to individual ionizing events; therefore cannot be used as a rate meter detection device

Dosimetry report
•Occupational exposure documentation and records are maintained;
1. Radiation safety program control and evaluation
2. Regulatory compliance
3. Epidemiological research
4. Litigation
•Report provided for each dosimeter submitted

Information on a Personnel Monitoring Report
•Group number
–Number assigned to Red River College
•Date of report
•Description  of the type of service
–TLD service, Quarterly , X-ray/Gamma/Beta
•Period Start-End (1)
–The wearing period start and end dates
•Dosimeter serial # (2)
•Full name (3)
–Surname, First given name, Second given name
•Multiple Group (4)
–“Yes” indicates person is active in more than one group. Cumulative totals are all inclusive . Blank indicates person is active in one group only.
•Type/Location (5)
–Dosimeter type and wearing location
•Current dose (6)
–Current period dose
•Cumulative dose (mSv) Year (7)
–Cumulative dose for current year
•Cumulative dose (mSv) Life (8)
–Cumulative dose for life time
–*See descriptions at the end of the report for details

Additional information
•Statkiewicz Sherer6thEdition
–P. 84 –85 Table 4-2 “ Advantages and Disadvantages of Personal Dosimeters”
–P. 76 Fig. 4-6 “Personnel monitoring report…”

Section 2.3
Radiation detection and measurement
•Instruments used to measure cumulative radiation intensity are called radiation dosimeters
•Instruments used to detect radiation are called radiation detection devices

Methods of Detection
•Radiation may be detected by the following methods
–Photographic effect

•Ionization chamber
–Gas filled chamber, negative and positive electrodes, dc amplifier, and an electrometer
•Radiation produces ion pairs → ions attracted to opposite electrodes → flow of electrons is a measure of radiation intensity
•Measures radiation by detecting the number of ionizations within a known volume of air
–Refer to Concepts of Radiation Protection –Information Sheet 2.1
•Measures either the total quantity of electrical charge or the rate the electrical charge is produced
•E.g. Cutie pie, proportional counter, and the Geiger-Muller (GM) detector
•Used in areas around a fluoroscope, radionuclide generators and syringes , vicinity  of NM or therapy patients, outside of protective barriers, and for precise calibration of diagnostic x-ray equipment
Calibration  Instruments
•Used to calibrate radiographic and fluoroscopic x-ray equipment
•The ionization chamber is connected to an electrometer
–Both the ionization chamber and the electrometer must be periodically calibrated to meet provincial and federal requirements
•Used by medical physicists to perform standard measurements, i.e. x-ray output  (mR), reproducibility and linearity of output etc.

Proportional Counter
•Proportional counters  are sensitive instruments, generally used in laboratory settings to detect small quantities of radioactivity
–Proportional counters detect alpha and beta radiations

Geiger-Muller Detector
•Used for contamination  control in nuclear medicine laboratories
–A portable instrument may be used to detect the presence of radioactive contamination on work surfaces and laboratory apparatus
•Very sensitive instruments able to detect one ionizing event
–May be equipped with audio amplifier and a speaker therefore allowing one to hear the crackle  of individual ionizations

Radiation Survey Instruments: Requirements
1. Easy to carry enabling one person to efficiently operate the device
2. Durable to withstand normal use
3. Must be reliable
4. Interact with ionizing radiation in a similar manner to how human tissue reacts
5. Should be able to detect all common types of ionizing radiation
6. The energy nor the direction of the incident radiation should not affect the units performance
7. Cost effective including maintenance charges
Section 2.4
Radiation protection organizations
•Safety standards, recommendations and guidelines in place today are based on the work of various radiation protection organizations throughout the world
•Organizations are divided, and serve either international or national functions
•Organizations may focus on:
–Biological Effects of Radiation
–Radiation Protection

International Organizations

•International Commission on Radiological Protection
•Established : 1928
•Provides recommendations on occupational and public dose limits.
•Recommendations are based on research and findings from various research councils . i.e. BEIR

•United Nations Scientific Committee on the Effects of Atomic Radiation
•Established: 1955
•Examines the risks and responses of human and environmental radiation.
•Makes predictions about the incidence  of biological effects among the general population.

•National Academy of Sciences/National Research Council on the Biological Effects of Ionizing Radiation
•Established in 1963
•Serves to advise agencies and governments of  the health effects of radiation exposures
•Publishes reports on the most current studies and findings.
•Radiation Effects Research Foundation
•Members: Gov’tof Japan
•Studies the survivors of atomic bombs at Hiroshima and Nagasaki
•Publishes results of studies/research.
National Organizations

•Canadian Radiation Protection Association
•Promotes research, scientific study and educational opportunities in radiation protection.

•Canadian Nuclear Safety Commission
•Established: 2000
•Federal regulator of nuclear facilities and materials in Canada
•Responsible for setting dose limits to protect workers [nuclear power workers and medical personnel working with ionizing radiation] from overexposure
•Also sets dose limits to ensure the general public is not overexposed to radiation from licensed nuclear facilities or substances  in Canada

•Radiation Protection Bureau-Health Canada
•Provides medical and technical advice
•Coordinates Canada’s preparedness  for nuclear emergencies
•Houses  the Canadian Radiological Monitoring Network and Laboratory
•National Dosimetry Services
–Provides personal radiation monitoring to 100,000 Canadians using ionizing radiation in their work
•National Dose Registry
–A centralized radiation dose record system, which contains the occupational radiation dose records of all monitored radiation workers in Canada.

RPB-HC Publications
•Safety Code 35: Radiation Protection in Radiology –Large Facilities: Safety Procedures for the Installation, Use and Control of X-ray Equipment in Large Medical Radiological Facilities
•Major objectives:
•Minimize patient exposure to ionizing radiation while ensuring diagnostic information
•Ensure adequate protection of personnel
•Ensure adequate protection of other personnel and the general public

Health Canada Publications: RED Act
•Radiation Emitting Devices Act
•Serves to regulate any radiation emitting equipment in Canada
•SC35 Appendix VI: Radiation Emitting Devices Regulations for Diagnostic X-ray Equipment

Safety Code 35: Terminology
•Must: indicates a requirement that is essential to meet currently accepted standards of protection
•Should: indicates an advisory recommendation that is highly desirable and is to be implemented  where applicable

Example of Terminology
•4.1Protective Equipment (P. 35)
5.Protective gonad shields for patients must have a lead equivalent of at least 0.25 mm Pb  and should have a lead equivalent thickness of 0.5 mm at 150 kVp.

Provincial Organizations
Radiation Protection Services:
*Department of Medical Physics
*Cancer Care Manitoba
•Ensures operational compliance  with:
–The Manitoba Regulation 341/88R:
X-ray Safety Regulation –Public Health Act
–RED Act
Cancer Care Manitoba
–Equipment registrations
–Shielding inspections
–X-ray equipment survey and inspection
–Radiation Protection Reports
–Radiation Monitor Service
–Education and Consulting

Section 2.5
Radiation-induced responses and goals of radiation protection
Biologic Effects of Ionizing Radiation
•Somatic effects
–Occur in the body of the irradiated person
–Importance of good safety practices
•Genetic effects
–Damage sustained  by an individual’s germ cells that is transferred to their offspring
–Importance of gonad protection
Categories of Radiation-Induced Responses
1. Deterministic  (nonstochastic) effects
2. Stochastic  effects
1. Deterministic Effects
•A.k.a nonstochasticeffects
–Biologic somatic effects directly related to the radiation dose received
–A threshold exists  below which no biological damage is observed
–Above the threshold dose the severity of the effect increases with increasing dose.
–Generally, high radiation doses are required to produce deterministic effects

Early Deterministic Effects
– Erythema
– Leukocytopenia
– Epilation
•More serious early deterministic effects are noted after very high levels of radiation exposure
–Acute radiation syndromes
Late Deterministic Effects
•These effects may be observed months or even years after high levels of radiation exposure
–Cataract  formation
–Organ atrophy
–Loss of parenchymal cells
–Reduced fertility
2. Stochastic Effects
•Described as “mutational, nonthreshold, randomly occurring biologic somatic effects…”
•The severity of the effect is not dose dependent
•Based on probability, therefore with each successive  exposure the probability of sustaining  a stochastic effect increases
•Examples of stochastic effects are cancer and genetic damage
•Stochastic events are termed “all-or-nothing” responses
•There is no minimal safe dose
–This explains the concern of the increased use of ionizing radiation (i.e. CT scans) to the general population

Occurrence  of Radiation-induced Malignancy
•To develop cancer it is the somatic cells that absorb the dose
–The dose may be 0.5 Gy or 2 Gy, either has the potential of causing radiation induced cancer
–The cancer will not be more severe if 2 Gy of radiation was absorbed versus  0.5 Gy
–However, the probability of radiation induced cancer would be greater at 2 Gy versus 0.5 Gy

Damage to Reproductive Cells
•When ionizing radiation is absorbed in the germ cells  (ova/sperm), mutations may occur with the potential of negative affects on future generations

Risk of Cancer Induction
•Data used when assessing  the risk of cancer induction has been from groups who were exposed to high doses of radiation (i.e. atomic bomb survivors)
•Estimates  have been extrapolated  from high dose data to determine the effects from low-level ionizing radiation exposure
•Consideration to the naturally occurring risks of cancer, birth defects and genetic mutations

ALARA Concept
•ICRP Publication No. 37 and Publication No. 55 referred to ALARA as “optimization ”
•By practicing ALARA the doses received by occupational and non-occupational workers is well below the allowable dose limits
•The model (dose-response curve) used in the ALARA concept depicts  no threshold dose therefore overestimating  the risk of injury

Objectives  of Radiation Protection
1.To prevent any clinically significant radiation-induced deterministic effects
–This may be achieved by adhering  to the dose limits based on recommendations by ICRP, specified in ICRP Publication 60
2.To limit the risk of stochastic responses to a moderate level
–This may be achieved by ensuring justification and optimization for every x-ray examination ordered
Current Philosophy
•Assumption  of a linear, nonthreshold relationship between ionizing radiation dose and biological response
–There is no known safe level of radiation dose
•The premise  that ionizing radiation posses both a beneficial and a destructive potential
–The benefit of exposure to ionizing radiation must outweigh the potential risk
Information Sheet 1.2

Section 2.6
Radiation exposure risk and dose limits
•Any exposure to ionizing radiation has risk associated with that exposure
•One way to illustrate  that risk is to compare a dose received during a certain diagnostic examination to a comparable dose received by background  radiation
–BERT = Background Equivalent Radiation Time
•Another way to evaluate risk is to compare radiation workers with other “risky conditions”
–Smoking cigarettes, driving “fast”, having heart disease, etc.
ICRP Recommendations
•In 1991 ICRP recommended that the annual dose limit for radiation workers be lowered from 50 mSv to 20 mSv
–This decision was made based on new information obtained from the Japanese atomic bomb survivors
–Damage was determined to be 3 –4 times greater than previously estimated
•SC 35 has incorporated the new 20 mSv annual dose limit for radiation workers

•The BEIR V report adopted  the linear no-threshold view based on extrapolated  data from atomic bomb survivors who received doses > 0.5 Sv(50 rem)
–Recall that annual natural radiation doses average 2.5 mSv in Canada and 3.3 mSv USA
•The RERF has determined that atomic bomb survivors have received an apparent threshold dose of 0.2 and 0.5 Sv
•The doses of 0.2 and 0.5 Sv correspond  to the average natural radiation received in a persons lifetime
•Research has demonstrated that atomic bomb survivors that have been exposed to moderate levels of radiation (5 mSv to 50 mSv equivalent to 1½ to 15 years of natural radiation exposure) have a reduced cancer rate when compared to the normally exposed control population
•The data collected by RERF appear to contradict  the BEIR V report which suggests that any amount of radiation has the potential to be harmful
•Other studies that have been conducted  draw  similar conclusions i.e. lower cancer rates in individuals exposed to higher levels of radiation

Radiation Hormesis
•These studies suggest a beneficial consequence of moderate radiation exposure (2 or 3 times natural radiation levels)
•The explanation for such a phenomenon suggests that radiation stimulates hormonal and immune responses to other toxic environmental agents responsible for cancer induction
•The radiation hormesis theory is yet to be proven
•Therefore MRTs must continue to practice ALARA as an ethical approach to managing radiation exposure
Table AI.1 suggests maximum values. All doses must be kept ALARA and any unnecessary radiation exposure must be avoided
Applicable  Body Organ or Tissue Radiation Workers (mSv)
Members of the Public (mSv)
Whole Body 20 1
Lens of the eye 150 15
Skin 500 50
Hands 500 50
All other organs 500 50

SC35: Appendix I
•There is no recommended discrimination  in dose limits between men and women of reproductive capacity (11 to 55 years)
•Technologist-in-training and students must adhere  to the dose limits of the general public
•Some provincial or territorial jurisdictions  may have different dose limits for some radiation workers; consult Appendix V
•Once pregnancy has been declared  by an RTR, the fetus  must be protected from X-ray exposure for the duration of the pregnancy
–Effective dose limit of 4 mSv for remainder  of the pregnancy from all sources of radiation
–Occupational exposure to pregnant RTRs generally arise from scatter radiation. Fetal  monitoring may be accomplished by placing a TLD on the surface of the abdomen

SC35: Section A: Responsibilities and Protection
1.0Responsibility of Personnel
–All personnel considered to have responsibility for radiation safety must work together for optimal results
1.1 Owner
1.2 Responsible user
1.3 X-ray equipment operator
1.4Medical physicist/Radiation safety officer
1.5Referring physician / Practitioner
1.6Information systems specialist
1.7Repair and maintenance personnel
1.1 Owner (P. 7)
–Ultimately  responsible for the radiation safety of the facility
–Must ensure the equipment and facility meet applicable radiation standards
–Must ensure a radiation safety program is developed, implemented  and maintained for the facility
–May delegate  these responsibilities to qualified staff
1.2 Responsible user (P. 7: 1-11)
–Main role is to monitor and manage the safety program of the facility including
•Personnel requirements
•Equipment performance and safety procedures
•Communicate safety program information
–There must be at least one person designated as a responsible user
–If the responsible user performs examinations on patients then all requirements listed in 1.3 also apply
1.3 X-ray equipment operator (P. 8: 1-11)
–Must carry out requested radiological procedures in a manner that minimizes unnecessary exposure to the patient, themselves and other workers
–Physician, physician/practitioner or a radiation technologist may be considered X-ray equipment operators

1.4 Medical Physicist/Radiation Safety Officer (P. 8-9: 1-17)
–Act as an advisor on all radiation protection aspects during initial construction stages, installation of the equipment and during ensuing  operations
•Medical physicist is a HCP with specialized training in medical applications  of physics
•Radiation Safety Officer (RSO) title assigned to a radiation safety specialist who manages the facilities radiation protection program

1.5 Referring Physician/Practitioner (P. 9: 1-4 and 1 –2)
–The individual authorized to prescribe diagnostic or interventional X-ray procedures
–Must ensure the X-ray is justified
–Some jurisdictions authorize  a registered nurse or nurse practitioner to order X-rays

1.6 Information System Specialist (P. 9-10: 1-7)
–Facilities that perform digital image processing should have access to a trained individual specializing in information technology software and hardware (required for PACS and teleradiology)
•Individual may be on-site  or available upon request
–Information system specialist must ensure confidentiality of patient records

1.7 Repair and Maintenance Personnel (P. 10: 1-7)
–Authorized  to perform hardware and software repairs and maintenance on X-ray generators, control systems, imaging systems and their operating software
•Individual may be on-site or available upon request
•May be contracted to an outside organization or equipment manufacturer

Unit 3
Radiation Safety Regulations
Section 3.1 Equipment and apparatus design
Section 3.2 Protective structural shielding
Section 3.3 Design and plan of x-ray facility
Section 3.1
Equipment and apparatus design
Protective tube housing
Control panel
Radiographic table
SID indicator
Skin sparing
X-ray beam limitation devices
Compensating  filters
Exposure reproducibility
Exposure linearity
Screen-film combinations
Radiographic grids
Mobile radiography
Digital imaging
Fluoroscopic procedures
Mobile C-arm fluoroscopy

Control Booth
•Provides protection for the operator
•Viewing window to observe the patient
•Provides shielding so no operator is occupationally exposed to more than 0.4 mSv/week
•Mobile protective screens must not be considered adequate as a control booth for radiological procedures.
•Whenever possible; radiation is scattered at least twice before entering the booth

Skin Sparing
•Device to minimize skin exposure
•Extends from the collimator (spacer bars) therefore prevent the collimator from being closer than 15 cm to the patient

Section 3.2
Protective structural shielding
•Structural protective barriers such as walls and doors
–Most common materials used are lead and concrete
•Effectiveness can be estimated if the half-value layer (HVL) or tenth-value layer (TVL) of the barrier material is known

Half Value Layer (HVL)
•“The HVL is that amount of absorbing material that will reduce the intensity of the primary beam to one-half its original value.”
–P. 165 Carlton
•“The HVL of a beam is an indirect measure of the photon energies of a beam…”
–P. 48 Bushberg

Tenth Value Layer (TVL)
•“TVL is analogous to the HVL, except that it is the thickness of material necessary to reduce the intensity of the beam to a tenth of its initial value. The TVL is often used in x-ray room shielding design calculations.”
–P. 49 Bushberg
SC35 P. 65 – Table AIII.1


Primary Protective Barriers
•To prevent direct or unscattered radiation from reaching personnel or the general public on the other side of the barrier
•SC35; Appendix III P. 61
Secondary Protective Barriers
•Protects against secondary radiation (leakage and scattered radiation)
•A secondary barrier is never struck  by the primary beam
•SC35; Appendix III P. 63
Control-booth Barrier
•Considered a secondary protective barrier
•X-rays should scatter a minimum of two-times before reaching an area behind this barrier
–Maximum permissible exposure rate is 0.04 R/week (SC35; Appendix III 2.2 P. 66)
•Patient’s observed through lead glass window

Shielding Guidelines
1. Distance between area to be shielded and operational positions of the X-ray tube
2. Designated  as a controlled or uncontrolled area
3. Occupancy factor (T) of the area
4. Primary or secondary barrier required
5. Use factor (U) of the required protective barrier
6. Workload (W) of the x-ray unit
7. Maximum and average tube potentials and output

Controlled and uncontrolled areas
1. Controlled
–Areas occupied by radiation workers
–Subject to limit of 20 mSv per year
2. Uncontrolled
–Areas occupied by non-radiation workers e.g. general public
–Subject to limit of 1 mSv per year

Workload  (W)
•Indicates the operational  time or amount of use of the X-ray equipment
•The workload distribution considers a range of operating voltages
•Expressed in milliampere-minutes per week (mA-min/week)
• SC35 Table 5: Typical Workloads (NCRP 2004) (P. 20)

Occupancy factor (T)
•Defined as the time an area is normally occupied, expressed as a fraction  of time
•SC35 Table 6: Occupancy Factors (P. 20)
•Guide for determining occupancy factor
–T=1 indicates areas full occupied by individuals, attended  waiting rooms, children’s indoor play area, etc.
–T=½ room used for patient examinations and treatments
–T = 1/5 corridors, patient rooms, staff lounges , staff rest rooms

Occupancy factor (T), CS35 P 20
Table 6: Occupancy Factors
Administrative offices and receptionist areas, laboratories, pharmacies and other areas fully occupied by an individual, attended waiting rooms, children’s indoor play areas, adjacent  X-ray rooms, image viewing areas, nurses’ stations, X-ray control rooms, living quarters .
Rooms used for patient examinations and treatments.
Corridors, patient rooms, staff lounges, staff rest rooms.
Corridor doors.
Public toilets, unattended vending  areas, storage rooms, outdoor areas with seating, unattended waiting rooms, patient holding areas.
Outdoor areas with only transient  pedestrian or vehicular traffic, unattended parking lots, vehicular drop off areas (unattended), attics , stairways, unattended elevators, janitor’s closets .

Use factor (U)
•Defined  as the fraction of operational time when the useful beam is directed at barrier, expressed as a fraction of a workload
• SC35 Table 7: Use Factor for Primary Barrier (P. 20)
•Guide for determining actual use factors for primary protective barriers
–U=1 indicates full use; floors of radiation rooms, walls containing a vertical image receptor, etc.
–U=¼ indicates partial use; doors and wall areas of radiation rooms not routinely exposed to the direct radiation beam
•Note: The use factor for secondary protective barriers is always taken to be 1 (U=1)

Use factor (U)
CS35 P 20
Table 7: Use Factor for Primary Barrier
Primary Barrier
Floors of radiation rooms, walls containing a vertical
image receptor; any other walls, doors or ceiling areas
routinely exposed to the direct radiation beam.
Doors and wall areas of radiation rooms not routinely
exposed to the direct radiation beam.
Ceiling areas of radiation rooms not routinely exposed
to the direct radiation beam.
Secondary Barrier
The use factor for secondary protective barriers is always taken to be 1.
Primary Protective Barrier
K= (Pd^2)/WUT
P = maximum permissible  weekly exposure rate expressed in R/week. For controlled areas P = 0.04 R/week; for uncontrolled areas P = 0.002 R/week.
d = distance in meters
W = mA-min/week
U = use factor
T = occupancy factor
K = exposure per unit workload at unit distance, expressed in R/mA-min at 1 meter

Barrier Against Leakage Radiation
•Calculate the barrier thickness required to protect against leakage radiation; first must determine the transmission  factor (B)
•Once the transmission factor is calculated, the barrier thickness expressed in HVL or TVL can be determined; SC35: Figure AIII.3 P. 64
•Once the HVL/TVL is known the barrier thickness in mm of lead or cm of concrete is obtained from Table AIII.1 P. 65

Barrier Against Scatter Radiation
•Scatter radiation has a much lower exposure rate and usually lower energy than the incident beam
•*Above 500 kV operating potential; scattered X-rays assumed to have the same penetrating capability as the primary beam
•< 500 kV operating potential; K is calculated
–Curves shown in Figures AIII.1 & AIII.2 (same curves used when determining primary protective barrier) to determine thickness of lead or concrete required

Computed tomography scanner shielding
Ct scanner shielding
•All walls in the CT scanner room are secondary barriers
–The detector array provides the primary radiation barrier
•Scatter radiation data is depicted  as exposure lines from the isocenter  of the gantry on a per slice basis for a known mAs
–Bushberg 2nd Edition P. 770 Figure 23-11
•Workload estimates are calculated from;
1. The average number of patients per week
2. The fraction of head versus body scans (scatter is different for the head versus the body)
3. The average mAs per patient
•Based on the number of slices and technique i.e. conventional versus helical  acquisition
•Scatter radiation for CT scanners has increased with the advent  of multislice detector arrays and larger collimation openings
•The outcome of this advanced technology is increased shielding requirements

Unit 4
Minimizing Radiation Exposure to Patients
Sect. 4.1: Patient Considerations
Sect. 4.2: Technical Considerations
Sect. 4.3: Patient Groups Requiring Unique Considerations
Section 4.1
Patient Considerations
•Effective communication
•Protective shielding
–Gonad shielding
•Male and female gonad shielding
•Placement of gonad shielding
•Types of gonad shielding
–Safety Code 35

Effective Communication
•Good communication builds rapport , reduces anxiety and emotional stress, and enhances the professional image of the MRT
–Clear and concise  patient instructions maximize cooperation and alleviate  patient fears about the procedure
•Effective communication will reduce the need for repeat exposures

•Serves to reduce motion blur on radiographs
•Voluntary motion
–Reduced through the use of suitable  immobilization devices, e.g. velcro, sandbag, pigg-o-stat
•Involuntary motion
–Minimized by reducing exposure times and compensating the mA
–High speed image receptors

Protective Shielding
•The purpose of protective shielding is to adequately attenuate ionizing radiation and therefore reduce or eliminate biological damage to radiosensitive organs and tissues
–Reproductive organs
–Lens of the eye
•Specific area shielding uses lead or lead-impregnated  material
Gonad Shielding
•Serves to reduce the exposure to reproductive cells and rapidly dividing cells
•By reducing gonad radiation exposure to the patient will in turn reduce the genetically significant dose to the population
•Used as a secondary protective measure; not a substitute  for adequate collimation

Gonad Shielding for Males & Females
•Gonad shielding (1 mm lead equivalency), when properly applied, may reduce exposure by ~ 50% for female patients and ~ 90 – 95% for male patients
•Should be used when their placement will not obstruct the area of interest
Placement of Gonad Shields
•Supine female patient
–When placing a contact shield, palpate the ASIS placing the shield ~ 2.5 cm medial to each ASIS
•Supine male patient
–When placing a contact shield; the top of the shield should be placed at the level of the symphysis pubis
•Note: The symphysis pubis is at the same level as the greater trochanter
Types of Gonad Shields
1.Flat contact shields
–Made of lead strips or lead impregnated materials
–Placed directly over patient’s reproductive organs
–Suitable for recumbent positions
–During fluoroscopy procedures consider the direction of the primary beam
2. Shadow shields
–Made of radiopaque material
–Suspended from above collimator device; hangs over the area of interest casting  a “shadow” in the primary beam
–Not suitable during fluoroscopy
3. Shaped contact shields
–Made of radiopaque material contoured  to fit the male reproductive organs
–Placed within a disposable or washable athletic supporters or jockey-style  briefs
–May be used in recumbent or non-recumbent positions; not suitable for the PA projection
–Suitable for use during fluoroscopy
4. Clear lead shields
–Made of transparent lead-plastic material impregnated with ~ 30% lead by weight
–Attach to the collimator
–Offer breast and gonad protection
•Scoliosis series

Safety Code 35
3.4 Guidelines for reduction of dose to sensitive tissue
–“Medical X-ray exposures are, at present, the major contributor of gonadal radiation exposure to the population.”
–Important factors to reduce dose to sensitive organs
1. Correct collimation of the X-ray beam. Irradiation of gonads, female breast tissue, and thyroid should be avoided if possible.
2. Examinations of children and adolescents should not be performed unless a condition exists indicating that benefit of the diagnostic information outweighs the radiation risk.
3. Appropriate use of specific area gonad shielding is strongly advised:
i. Gonads lie within or in close proximity to the X-ray beam
ii. Patient is of reproductive age
iii. Clinical objectives will not be compromised
4. Appropriate selection of tube voltage (kVp), current (mA) and filtration is particularly important when the gonads or breast tissue lie within or near the X-ray beam
5. Doses are related to the sensitivity of the imaging system. The more sensitive an imaging system results in decreased gonad dose versus decreasing the sensitivity of the imaging system will increase gonad dose

Section 4.2
Technical considerations
•Tube voltage and beam filtration
•Field area and geometry
•X-ray image receptors
•Air-gap technique
•Repeat images
•Computed tomography
Tube Voltage
•Goal is to achieve a balance between image quality and dose to the patient
•Increasing the kVp will result in a beam with more penetration; therefore less absorption
•To maintain image density (brightness); the mAs is reduced
•Within limits; the compromise between kVp, image quality (contrast) and patient dose

Beam Filtration
•The x-ray beam is polychromatic ; therefore removal of the low-energy x-rays in the beam will reduce patient dose
–Low-energy x-rays contribute very little to image formation; however do impart  a dose to skin and shallow  tissues
•As tube filtration increases; the beam becomes harder; due to fewer low-energy photons
Table 8: Minimum Half-Value Layers of aluminum for given X-ray tube voltages
X-ray tube voltage (kV)  Half-Value layer of Aluminum (mm)
70 2.5
80 2.9
90 3.2
100 3.6
110 3.9
120 4.3
130 4.7
140 5.0
150 5.4
Field Area
•Ensuring the collimation field size exposes only the necessary tissue
•There is a further  benefit; reduction of scatter radiation
•A reduction in scatter radiation incident on the image receptor (detector) will improves image contrast

•Increasing the SOD and the SID helps to reduce patient dose
•The reduced beam divergence  limits the volume of tissue irradiated; thereby reducing the integral  dose
•Though a minor contributing factor; dose to the patient from leakage radiation is also reduced
•For a fixed SID; it is important to increase the SOD as much as possible

Source-to-skin distance
•As the SSD decreases, entrance skin exposure increases, therefore using the greatest SSD that is practical will reduce patient dose
•SC35 refers to SSD as “focal spot-to-skin” distance
– P. 13; The focal spot-to-skin distance should be as large as possible, consistent with good radiographic technique.

X-ray Image Receptors
•As the speed of an image receptor increases the number of x-ray photons required to produce a given optical density (brightness) decreases
•As the speed of a film-screen image receptor increases; patient dose decreases; image quality may be compromised
•Digital radiographic image receptors (CR, DR) produce images with a wide dynamic range allowing manipulation of the brightness and contrast post-exposure
•Image intensifiers (radioscopic equipment) also has a wide dynamic range with the entrance exposure varying per image

High-speed Systems
•High speed imaging systems reduce patient dose
•The mAs required to produce a diagnostic image in reduced; the resulting image may demonstrate quantum mottle
•Quantum mottle degrades  image quality by giving the image a “noisy/blotchy ” appearance

Acquiring an Image
1. Conventional radiography
–Also known as film/screen radiography
–In darkroom conditions a radiographic film is placed in a light-tight cassette
–The cassette is exposed to x-rays; an invisible or latent  image is produced on the film
–In darkroom conditions the film is removed from the cassette and chemically processed; this allows the invisible image to be visible
–No changes in the image quality may be made after processing; the image is permanent
2. Computed radiography (CR)
–CR reader will load the imaging plate (IP) into the image receptor, read the IP (laser stimulation resulting in light emission), erase the IP (IP exposed to intense light) and re-load the IP into the image receptor
–The steps involved in producing a CR image are similar to those required for conventional radiography
–The CR image is viewed on a computer allowing post-processing capabilities
–The CR image may be saved to a PACS system or sent to a laser printer to produce a “hard copy”
3. Digital radiography (DR)
–No cassettes or image receptors are required
–The anatomy of interest is placed on the radiation detector and the exposure is made; an electronic latent image is produced
–The DR image is viewed on a computer allowing post-processing capabilities
–The DR image is saved to a PACS system

Digital Imaging
•The digital image is displayed  on a monitor
•The MRT has the ability to manipulate the brightness (by adjusting the window level) and contrast (by adjusting the window width) of the image
•Evidence has suggested that MRTs are unnecessarily and unethically overexposing patients during an initial examination therefore avoiding the possibility of a repeat exposure
•MRTs must follow the ALARA principle at all times
•The kVp chosen should be adequate to penetrate the anatomy of interest
•The CR IP is very sensitive to scatter radiation
–Close collimation
–Use of a lead divider when performing multiple exposures on one IP
–Use of a grid for thicker body parts

Radiographic Grids
•When body tissue thickness increases higher kVp values are required to penetrate the tissue
–This results in an increase in scatter x-ray production
–Scattered radiation degrades the image
•Lowers the contrast of the image; more shades of grey
•Grids serve to remove scattered x-ray photons before they reach the image receptor
– This improves the quality of diagnostic information on the image
-Using grids increases the patient dose
-This increase can be justified

Grid Ratio and Patient Dose
•Grid ratio refers to the amount of lead (radiopaque material) in a grid; the higher the grid ratio the greater the lead content
•mAs is increased to compensate for the use of the grid
•Therefore the patient dose increases as grid ratio increases
–It is important to select the lowest grid ratio possible that will result in a diagnostic image
Air Gap Technique
•A technique that reduces scattered radiation from reaching the image receptor
•Accomplished  by increasing the object-to-image-receptor (OID) distance
–Routinely used in lateral C-spine examinations
•An increased OID will result in the anatomy appearing more magnified on the image
–To compensate for this; simply increase the SID
–Lateral C-spine examinations are done at 180 cm SID
Repeat Images
–Any radiograph that must be performed more than once due to human or mechanical error
•The additional exposure increases patient dose i.e. doubling the dose
–Occasional  repeat radiographs are acceptable i.e. to obtain a diagnostic image
•Careful positioning and setting of technical factors to minimize repeat exposures

Nonessential Radiologic Examinations
•A request for an x-ray examination must include clinical information to substantiate  and correlate  with the specific examination being requested i.e. CXR requested with clinical information “pain in left hip”
•Pre-employment CXR, CXR as part of a routine health check-up, CXR for mass screening for TB
•Whole-body multislice spiral CT screening

Referring Physician/Practitioner must:
•Posses relevant  qualifications to be authorize  by legislation  to order x-rays
•Order an x-ray examination based on professional experience, judgment, and common sense
•Give consideration to alternate , non x-ray utilizing  examinations
•Be confident that the procedure will improve the patient diagnosis/treatment sufficiently in comparison  with alternate non x-ray utilizing examinations
•Be aware of the risks associated with x-ray procedures
SC35 P.9 1.5 Referring Physician/ Practitioner

Repeat Analysis Program
•Repeat analysis is a method of tracking the reason for repeating radiographs
•Technologists are asked to indicate, on a chart or via electronic documentation, the reason a repeat exposure was necessary, i.e. patient motion, poor positioning, insufficient exposure factors used etc.
•A designated  person in the department (generally a technologist who has been assigned this QC duty) compiles the data and is able to categorize the main reasons for repeat exposures i.e. equipment malfunctions, improper CR placement, processing errors, etc.
•The outcome of the analysis will vary depending on the results obtained i.e. staff education sessions  on a position (i.e. AP open mouth C1-C2 that had a high repeat rate, service on the x-ray or processing equipment
•The net benefit is reduced repeat exposures with the direct correlation of reduced patient dose
•A definite  win-win situation!
Fluoroscopic Procedures
•SC35 (P. 14): 3.3.3 refers to fluoroscopic procedures as radioscopic procedures
•Radioscopic procedures provide dynamic or in motion images of the anatomy resulting in high exposures compared to radiography
•Image intensification improves the radiologist’s perception  of the radioscopic image by increasing the brightness of the image; referred to as ABC (Automatic Brightness Control)
–SC35 (P. 14): indicates the operator of the equipment with ABC must monitor the X-ray tube current and voltage
•When magnification modes are chosen on radioscopic equipment a higher mA is required to maintain brightness of the image therefore increasing patient dose
•Using intermittent  or pulsed fluoroscopy as well as last image hold all reduce patient dose
–SC35 (P. 26): Last Image Hold
•Selection of appropriate kVp must once again be chosen according to part thickness to afford adequate penetration and therefore appropriate brightness of the radioscopic image
–Children require a decrease in kVp compared to an adult by as much as 25%, again depending on part thickness
•Adequate filtration of the radioscopic beam is required to reduce the patient’s skin dose
•Cumulative  timing device which SC35 (P. 26): refers to as chronometer, essentially indicating the amount of time X-rays have been emitted
SC35 (P. 25): indicates that the Protective Shielding of the Image Intensifier must intercept  the entire cross section of the x-ray beam and the x-ray tube must not be capable of emitting x-rays unless the protective shielding is in place to intercept the x-ray beam
•SC35 (P. 26): indicates the Irradiation Switch must require continuous pressure to produce x-rays and enable the operator to terminate x-ray production at any time

•Has the potential to impart  large doses due to continuous X-ray production for real-time image viewing
–Exposure techniques may be considered low, however over a period of minutes become substantial
–“Turbo” or high-level irradiation can increase the output of the system by a factor of 10 from typical fluoroscopy levels
•Bushberg (P. 777); Figure 23-14

Safety Code 35
P. 25-26; 2.5.3 Radioscopic Equipment Requirements 8. Maximum Air Kerma Rates – The following maximum air kerma rates apply to radioscopic equipment except during recording of radioscopic images:
Equipment not equipped with an automatic intensity control  Equipment equipped with an automatic intensity control  Equipment equipped with both an automatic intensity control and a high-level irradiation control and the high-level irradiation control is activated
50 mGy/min  100 mGy/min  150 mGy/min
Safety Code 35
P. 25; 2.5.3 Radioscopic Equipment Requirements
4.Focal Spot-to-Skin Distance – Equipment must be equipped with a device that limits the focal spot to skin distance
Mobile Equipment  Stationary Equipment  Special Application
30 cm  38 cm  20 cm
Mobile Radioscopic Equipment
•SC35 (P. 14): indicates that mobile equipment should only be used for examinations where it is not practical to transfer patients to a permanent radioscopic installation e.g. in a Diagnostic Imaging Department

Cine Fluorography
•Uses 35-mm cine film to record images during fluoroscopic examinations, i.e. heart catheterization
•Images are captured at different filming rates; 30 frames/sec to 120 frames/sec.
•Each frame captures an image by exposing the patient to a very short pulse of radiation
–There is a direct relationship between framing rates and patient dose

Interventional  Procedures
•Invasive procedures performed by a radiologist or cardiologist with the aid of fluoroscopy
–Involves insertion of a catheter into vessels (treat vascular occlusions or malformations) or directly into tissue (for drainage or biopsy purposes)
•Exposure rates are high for these procedures allowing for visualization of smaller and lower contrast objects

SC 35: (P. 14-15) “Angiography”
1. Exposure to patient’s eyes and thyroid can occur during cerebral angiography and cardiac catheterization and angiography. Appropriate shielding should be provided.
2. Keep irradiation time to a minimum.
3. Use increased tube filtration and lower time frequency (pulse radioscopy)
4. Keep x-ray tube as far as possible and the image intensifier as close as possible from the patient
5.Remove the grid for children and small adults
6.Aware that magnification mode may increase the dose to the patient
7.Use cine-run only as long as necessary; if possible use automated injection systems
8.If procedure is long re-adjust the x-ray tube so a different area of skin is subjected to the X-ray beam
9.Facility should have dose documentation of each type of interventional procedure

Dose-Area-Product (DAP) meters
•Measures output exposure in fluoroscopy systems during procedures
•A radiolucent ionization chamber positioned in the primary beam near the port of the x-ray tube
•Measures the accumulated ionization that occurs during fluoroscopy providing the physician with a real-time estimate  of accumulated patient exposure

Methods to Reduce Fluoroscopic Exposure
1. Limit the “beam-on” time by using short bursts  of exposure
2. A 5-minute cumulative timer allows a technologist to track  the fluoroscopy time
3. Using the last-image-hold device
4. Pulsed fluoroscopy reduces the framing rate to less than real time
5. Use of an optimal image intensification system
6. Limiting the field size with collimation
7. Maintain as much distance as possible between the X-ray tube and the patient’s skin
8. Use the magnification mode sparingly

Computed Technology (CT)
•With the advent  of computers it became possible to image the body in “slices” with subsequent  images corresponding to a 3D section of the patient versus the traditional 2D projection
•The use of CT technology has increased substantially  as physicians are relying more on these images to confirm a diagnosis

Computed Tomography
•Preamble : Automatic exposure control (AEC) allows the technologist to set an appropriate kVp for the thickness of body part under investigation
•Once the exposure switch is engaged  the length of the exposure (e.g. dose) imparted  is “automatically” terminated when the pre-determined density (brightness) has been received by the image receptor
•In computed tomography AEC is generally not available; therefore the scanners work at a fixed kVp and mAs regardless of patient thickness/size
•CT technologist must be trained to reduce the mAs (and perhaps the kVp) for smaller patients, particularly the young
•Bushberg (P. 779); Table 23-16

Image Gently
•The Image Gently™ campaign  was launched in an effort to reduce doses to the pediatric patient with a focus on CT, interventional radiography and NM
•The Image Gently site ( contains a wealth of information including dose reduction techniques, latest research and educational materials for all imaging stakeholders

Concept of a Smart Card
•We have discussed the increase in ordering and performing of CT procedures
•The outcome is an alarming increase in exposure to ionizing radiation with no means of tracking  patient doses
•There have been cases of ionizing radiation-induced injury from the use of high dose examinations, i.e. CT scan, interventional fluoroscopy
•The International Atomic Energy Agency (IAEA) is devising a system to track radiation dose data on patients
•With the advances in diagnostic imaging and interventional procedures the potential to track doses will ensure the risk to the patient remains within acceptable limits

Section 4.3
Patient groups requiring unique considerations
The Pregnant Patient
•Question the patient for possibility of pregnancy
•If patient believes she might be pregnant:
–Ask for the date of her last menstrual period (LMP)
–Determine if the exam is elective /critically important
–Consult with radiologist/physician if the exam is essential for the patient
SC35 3.2 Guidelines… Examination of Pregnant Women
•“Radiological examinations of the pelvic area of a woman known to be pregnant simultaneously irradiate the patient’s gonads and the whole body of the fetus.”
1. Only essential investigations
2. When required in pelvic or abdominal area; exposure must be kept to a minimum; if possible make use of protective shielding
3. Use the prone position if a radiological examination of the fetus is required
4. Radiography of chest, extremities, etc. for valid  reasons should have a well collimated X-ray beam and proper shielding of the abdomen
Pediatric Considerations
•As we have learned earlier in the course, children are more sensitive to radiation than are adults
•Children have a greater life expectancy therefore biological damage from radiation exposure may manifest  in their lifetime
•Every precaution must be taken to minimize exposure to our pediatric patients
•Children require smaller doses of radiation due to their smaller stature
•Children do not understand the importance of remaining still for an exposure therefore the MRT must consider creative techniques to elicit  their cooperation (age dependent), use immobilization techniques, minimize exposure times, and use fast imaging systems
•Some difficulties arise with gonad shielding in pediatric examinations
–On a well collimated beam with the gonad tissue more than 2 cm from the edge of the field of view, placement of gonad shielding does not significantly reduce gonad dose as the majority of the dose will be as a result of internal scatter
–In small girls the location of the ovaries require shielding over the iliac wings as well as the sacral area
•Collimation is very important in pediatric studies; PBL limits the field size to the IR size, however, our pediatric patients are often much smaller than the IR size
•Female patients may be imaged in the PA position versus the AP position to significantly reduce dose to the breast tissue
•CT examination protocols must be altered for the pediatric patient; scan kVp and mAs must be lowered
The Potentially Pregnant Patient
•The developing embryo and fetus are very sensitive to ionizing radiation, therefore it in imperative  that the MRT determine if their patient is pregnant
•SC35 recommends using the “10-day rule” to determine the possibility of pregnancy especially when the examination involves the pelvic area
–This will ensure x-ray examinations take place when the risk of pregnancy is the lowest

Elective Examinations
•Elective examinations of the abdominal area are not considered urgent and therefore do not need to be performed when there is a possibility of pregnancy
•An elective examination on a female of childbearing age should therefore be performed within the first few days of the onset of menses
Female Patient of Childbearing Age
•SC35 (P. 12) considers child bearing age to be between 11-55 years

•The guidelines suggest the MRT must ask whether there is a chance of pregnancy
–MRTs are requested to analyze the situation and consider all the information available to decide whether to proceed with asking a young teen this very delicate  question
•Information to consider but not limited to this list include:
–Does the child have sufficient body fat to have started to menstruate?
–Is the x-ray examination of an extremity or of the abdominal or pelvic area?
–Has the child been accompanied by a parent or guardian? Are you able to perceive  any apprehension  or tension?
•It is important to perform radiological examinations of the pelvic area in the ten-day period following the onset of menstruation as the risk of pregnancy is very small
•If the examination is unavoidable , care must be taken to minimize the dose to the fetus
SC35 (P. 12) 3.1.8

Additional topic in Textbook to Omit
•An additional area of the textbook to omit in the reading assignment includes:
–P. 260 – 263 The section titled “Irradiation during an Unknown Pregnancy” to “Sample Cases to Obtain an Approximate Estimate of the Fetal Equivalent Dose”
–We will consider this information in our study of Radiation Biology
Miscellaneous  Considerations
•Careful identification of the patient
•Elimination  of screening  examinations that rarely detect pathology
•Standing order x-rays, i.e. Pre-op CXR
•Frequent screening examinations, i.e. annual  dental x-rays
•Use of high speed imaging systems
•Screening mammography
–Family history of breast cancer, or other indication; above 40 to 50 years old
•Repeat examinations
–Average Repeat Rate is 4% to 6%; common to repeat portable examinations
–Continuous monitors of repeat examinations
•Pre-programmed techniques for examinations
–Eliminates the “guess  work” when selecting technique factors
•Technique charts posted beside the control panel
•Use of photostimulable phosphor imaging plates
–May reduce the need to repeat due to exposure factors*
•Equipment problems resulting in repeat exposures
–Eliminated by a periodic QC program

Unit 5
Minimizing Radiation Exposure to Personnel
Section 5.1 Dose Limits for Occupational Radiation Exposure
Section 5.2 Basic Principles of Radiation Protection
Section 5.3 Technical Considerations

Section 5.1
Dose limits for occupational radiation exposure
Dose reduction strategies
•“Methods and techniques that reduce patient exposure also reduce exposure for the radiographer.” (Statkiewicz Sherer 6th Edition P. 284)
–ALARA concept (U4)
–Avoiding repeat examinations (U4)
–Patient as a source of scattered radiation
–Scattered radiation – occupational hazard
–Filtration of the x-ray beam (primarily benefits the patient) (U4)
–Protective apparel
–Technical exposure factors
–Use of high-speed image receptor systems (U4)
Patient as a Source of Scattered Radiation
•Compton scatter is the primary source of scatter radiation in diagnostic imaging
–When x-rays interact with matter; energy is transferred to the recoil /Compton electron
–The amount of energy retained  by the scattered photon depends on the angle of deflection
–As the angle of deflection increases the amount of energy retained by the scattered photon decreases
Bushberg P. 39-40
–When Compton scattering does occur at the lower x-ray energies used in diagnostic imaging (18 to 150 keV), the majority of the incident photon energy is transferred to the scattered photon…
–For example, following the Compton interaction of an 80-keV photon, the minimum energy of the scattered photon is 61 keV. Thus, even with maximal energy loss, the scattered photons have relatively high energies and tissue penetrability.
•The probability of Compton interaction depends on the energy of the incident x-ray beam and the electron density of the absorber
–As the energy of the x-ray beam increases the probability of Compton interaction increases
–As the electron density of the absorber increases the probability of Compton interaction increases

– The intensity of scatter in various directions is a major factor in planning and executing  safe radiation procedures
– SC35: Appendix III Table AIII.3 (P. 66): Ratio of Scattered to Incident Exposure

Scattered Radiation – Occupational Hazard
•Scattered radiation is the greatest risk of occupational exposure
•The technologist that reduces the amount of scatter radiation will also reduce occupational exposure
•Strategies that the technologist may employ to reduce scatter include;
Protective apparel
– Protective lead aprons and shielded barriers protect personnel from scatter radiation
– Similar to the gonad shield protecting the patient
Technical Factors
•As the energy of the incident beam increases; the scatter radiation moving in a forward direction increases
–Primarily this forward scatter contributes to image fog
•As the energy of the incident beam increases the energy of scatter radiation decreases with increasing angle of deflection
–Factor to consider when the technologist is participating in a fluoroscopic procedure
–Standing 90⁰ (at a right angle) from the original point of scatter (from the patient) will result in a lowest dose from scatter radiation

SC35 2.3 P. 11
Requirements and Recommendations for Operation of Radiographic Equipment
1. Irradiation should be controlled from the control panel located in a shielded area
2. Operator must have a clear view of the patient during every x-ray examination without leaving the control booth
3. Radiographic cassettes must never be held by hand during an exposure

Holding Patients
•Ensure that the individual holding the patient is not standing or will not intercept the primary beam
•Pregnant women must never hold a patient during an exposure
•SC35: 2.1.10 (P. 11)
–Individuals must be provided with protective aprons and gloves
–No person should regularly perform these duties
Doors to x-ray Rooms
•Radiographic and fluoroscopic exposures are only to be made with the door(s) closed
SC35: 2.1.11 (P. 11) “All entrance doors to an X-ray room should be kept closed while a patient is in the room and must be closed while making an X-ray exposure.”
Table AI.1 suggests maximum values. All doses must be kept ALARA and any unnecessary radiation exposure must be avoided
Applicable Body Organ or Tissue  Radiation Workers (mSv)  Members of the Public (mSv)
Whole Body  20 1
Lens of the eye  150 15
Skin  500 50
Hands  500 50
All other organs  500 50
SC35: Appendix I
•Any irradiation involves risk; Appendix 1 are maximum values. Doses must be kept ALARA
•There is no recommended discrimination in dose limits between men and women of reproductive capacity  (11 to 55 years)
•Technologist-in-training and students must adhere to the dose limits of the general public
•Some provincial or territorial jurisdictions may have different dose limits for some radiation workers; consult Appendix V

Protection for Pregnant Personnel
Imaging Department Protocol
•It is common for pregnant personnel to continue to work in the DID
•Adhering to established safety procedures, once the technologist has declared her pregnancy, ensures the fetus is protected from x-ray exposure

Protective Apparel
•Maternity aprons may be available with a lead equivalency of 0.5 mm with an additional 1 mm lead equivalent protective panel across the width of the apron
•Alternate is to use a wrap -around protective apron with a lead equivalency of 0.5 mm
Work Schedule Alteration
•Generally an alteration in the technologists work schedule is not required i.e. re-assigned  to lower radiation exposure risk areas
–Consider the impact on other unknowing potentially pregnant technologists who are then re-assigned to work more frequently in high radiation exposure risk areas
•ALARA guidelines ensure all technologists rotate through the various exposure risk areas

•Please omit from your Chapter 12 reading the section titled “Acknowledge of Counseling and Understanding of Radiation Safety Measures” on page 286
–The concept of a pregnant technologist having to sign a document indicating she has received radiation safety counseling is not a practice in Canada.

According to SC35: 2.1.9 (P. 11)
•“A female operator should immediately notify her employer upon knowledge that she is pregnant, …to ensure that her work duties during the remainder  of the pregnancy are compatible  with the recommended dose limits as stated in Appendix I.”

SC35: Appendix I (P. 57)
•“… once pregnancy has been declared, the fetus must be protected from X-ray exposure for the remainder of the pregnancy.”
•“… occupational exposures to pregnant workers arise  mainly from scattered X-radiation.”
•“…the most effective method of monitoring exposures to the fetus, is to measure the equivalent dose to the surface of the abdomen using a thermoluminescent dosimeter.”
Section 5.2
Basic principles of radiation protection
Cardinal Principles of Radiation Protection
1. Minimize time;
2. Maximize distance;
3. Maximize shielding

Minimize Time
•Reducing time spent near a radiation source (x-ray tube) will reduce radiation exposure
•Dose is directly related to duration of exposure
–Minimum exposure time in fluoroscopy reduces patient dose as well as personnel exposure
Maximize Distance
•As the distance between the radiation source and person increases, the radiation exposure decreases
–Due to the radiation being distributed over a greater surface area
•Inverse square law    I_1/I_2 =((〖I_2)〗^2)/((〖I_1)〗^2 )

Maximize Shielding
•Shielding requirements are in place to reduce exposure to patients, staff, and the public
–Sources of exposure include primary radiation, scatter radiation, and leakage radiation
–Note: Protective structural shielding was discussed in Unit 3
•Protective shielding is donned  during fluoroscopy, mobile radiography, or when the technologist must be in the x-ray room

Protective Apparel
•Must be stored on designated racks
–If folded or heaped  in a corner, cracks can develop
•Integrity  of aprons and gloves should be checked a minimum of once per year; either with fluoroscopy or a high-kV radiography technique (120kV @10mAs)

Protective Lead Aprons
•Protective body aprons must provide attenuation equivalent to at least
a)0.25 mm of lead for examinations where peak x-ray tube voltage is 100 kV or less
b)0.35 mm of lead for examinations where peak x-ray tube voltage is greater than 100 kV and less than 150 kV
c)0.5 mm of lead for examinations where peak x-ray tube voltage is 150 kV or greater
SC35: 4.1.1 (P. 35)

Protective Gloves
•Protective gloves must possess  at least a 0.25 mm lead equivalency.
•The protection must be provided throughout the glove, including fingers and wrist
SC35: 4.1.6 (P. 35)

Section 5.3
Protection During Fluoroscopic Procedures
•MRT should stand as far away from the patient as is practical; only move close to the patient when they need assistance
•Protective apparel, as previously discussed, must be worn during fluoroscopic procedures
•When not assisting  the patient or the radiologist, the technologist should stand either directly behind the radiologist or in the control booth until needed to assist the patient
•Wear a wraparound protective lead apron as you are required to “move” around the X-ray room

Dose Reduction Techniques
•These techniques reduce dose to the technologist and radiologist during fluoroscopic procedures
–Adequate beam collimation, filtration, control of technical exposure factors, high speed image receptor systems, correct radiographic film processing, adequate structural shielding, appropriate source-to-skin distance, use of cumulative timing device

Remote Control Fluoroscopic Systems
•Remote control units provide the best protection from radiation exposure during fluoroscopic procedures
–The radiologist operates the fluoroscopic controls from behind a protective barrier
–The technologist also remains in the protected area until needed to assist the patient
•The patient is easily observed through the clear protective shielding

SC 35: 2.4 (P. 11)
Requirements and Recommendations for Operation of Radioscopic Equipment
1. All persons required to be in the room must wear protective aprons
2. Protective gauntlets  should be worn by the radiologist during palpation; during radioscopy palpation should be kept to a minimum
3. “All radioscopic examinations should be carried out as rapidly as possible using minimum dose rates and X-ray field size.”
4. “For each type of radioscopic procedure, an assessment  should be made of the physical position of all personnel to ensure ease of operation of the equipment, visibility of the display, and protection from the radiation field.”

Rotational Scheduling of Personnel
•Occupational exposure is highest during fluoroscopy, mobile radiography, and special procedures
•Scheduling technologist to spend less time in these high radiation exposure risk areas will help to reduce exposure
–Cardinal  principle of time to offer additional radiation protection

•Please omit from your Chapter 12 reading the following two sections titled; “Spot Film Device Protective Curtain” and “Bucky Slot Shielding Device” on pages 293-294
–These radiation protection devices will be discussed in your Imaging Equipment course. Also, please note that SC 35 values for lead equivalency would apply.

Protection During Mobile Examinations
•Use of protective apparel
–Must be worn when structural or mobile protective shielding is unavailable
–A protective apron should be assigned  to each mobile unit
•Distance as a means of protection
–SC35 recommends the technologist stands at least 3 meters from the x-ray tube
–Permits  technologist to use the ISL
•Where technologist should stand
–At minimum, the technologist should stand at a 90⁰ angle from the patient (versus at a 110⁰ or 140⁰ angle)
–However, distance and shielding have a greater influence on dose reduction therefore these factors should be considered first

SC 35: 2.2 (P. 11)
1. Mobile units should only be used when patient transfer to the x-ray department is inadvisable
2. During operation the x-ray beam should be directed away from occupied areas and efforts  made to ensure the beam dose not irradiate persons in the vicinity  of the patient
3.“The operator must not stand in the direction of the direct beam and must be at least 3 meters from the X-ray tube unless wearing personal protective equipment or standing behind a leaded shield.”
4. In a capacitor  discharge unit, after an x-ray irradiation has been made, the residual  charge must be fully discharged before the unit is left unattended .
Note: The residual charge can result in “dark current” an x-ray emission without depressing the exposure switch.

Protection During C-arm Fluoroscopy
•Personnel exposure from scattered radiation
–Mobile C-arm equipment is often operated by inexperienced  physicians
–Mobile C-arm has more flexibility in direction and placement of the equipment i.e. less standardized
–During the x-table configuration; high backscatter exposure on the side of the x-ray tube; due to increased energy of the beam entering the patient
–Technologist should never intercept the useful beam

Protection During C-arm Fluoroscopy
•Protective apparel for all persons in the vicinity
–Manipulation of the equipment into various positions and long fluoroscopy times render  the need for all individuals to wear protective apparel i.e. lead apron and thyroid shield
•Lead equivalency as stated in SC35 (P. 35)
•Individuals requiring personal monitors as stated in SC35 (P. 10)

C-arm Fluoroscopic Examinations
•Position of C-arm fluoroscope
–As we discussed in Unit 4; positioning the x-ray tube over the table and the image intensifier underneath results in a higher exposure to the patient and therefore increased production of scatter radiation – directly related to increased dose to personnel
–When possible; place the image intensifier over the table and the x-ray tube under the table

SC 35 Reference
•Refer to SC 35: Section B: Facility and Equipment Requirements: 2.5.3 Radioscopic Equipment Requirements
–Note: This area of SC35 was discussed in Unit 3 – Minimizing Exposure to the Patient

Protection During Interventional Procedures
Increased Importance of Radiation Safety
•Interventional procedures have the potential of increased dose to personnel due to the extended fluoroscopy times and multiple images that are acquired during the procedure

Dose Reduction  Techniques – Radiographer
•Use of high-quality low-dose fluoroscopy mode
•Pulsed beam operation
•Optimal beam filtration
•Removable grids
•Variable optical aperture
•“Road  mapping”
•Time-interval differences
•“Last-image-hold” mode
•Record cumulative exposure time on the requisition

Dose Reduction Techniques by Radiologist/Interventional Physician
•Shorten duration of the procedure
•Taking fewer images
•Reducing the use of continuous fluoroscopic mode
•Keep protective curtain on the image intensifier
•Regularly use the last-image-hold feature
•Use high-level-control sparingly  and only when increased visualization is critical and necessary (i.e. deployment  of a stent or embolization )

Extremity Monitoring
•Due to the proximity  of the hands and forearms to the primary beam, physicians may require extremity monitoring
•SC 35: Appendix I. indicates the dose limit for the skin of the face and hands is 500 mSv and is averaged over an area of no more than 1 cm²
–The reason for assigning  a dose limit is due to the possible __ effects during interventional procedures.

SC 35: Section A Reference
•In addition to SC 35 2.4 (P. 11-12)
2.4.1 Requirements and Recommendations for Performing Angiography
–One of the potentially greatest sources of exposure to personnel;
i. These procedures require a number of personnel in close vicinity  to the patient
ii. Radioscopy for an extended period of time
iii. Multiple radiographic exposures
1. Full use of protective devices provided; shielded panels, drapes , Bucky slot  covers, etc.
2. Operate equipment with the x-ray tube under the patient; if the x-ray tube is horizontal, stand on the side of the image receptor
3. All personnel must wear protective clothing and personnel dosimeters. Protective glasses should be worn.
4. All personnel not required to be next to the patient should stand back; preferably  behind a protective shield
5. Special shields in addition to the protective devices provided with the machine should be used.
SC35: 2.0 Procedures for Minimizing Radiation Exposure to Personnel
Review the General Requirements and Recommendations listed on page 10 – 11.
–Many of these will be familiar to you as we have discussed them previously
–Others are common sense
–Please take a moment to review the content is this section of SC 35

Unit 6
Doses from Radiographic Procedures
Sec. 6.1 Estimation of patient dose
Sec. 6.2 Patient dose in mammography
Sec. 6.3 Patient dose in CT
Sec. 6.4 Guidelines for reduction of dose to sensitive tissues
Sec. 6.5 Diagnostic reference levels (DRL)
Section 6.1
Estimation  of patient dose
Concern About Risk of Exposure From Diagnostic Imaging Procedures
•The public is becoming more aware of the potential risk of an exposure to x-rays
–Induction of a radiogenic cancer or genetic defect after irradiation
•A method to determine the amount of radiation from diagnostic imaging procedures include:
–Entrance skin exposure (simplest to determine)
–Mean  marrow dose
–Gonad dose

Estimation of Patient Dose
1.Entrance Skin Exposure (ESE)
2.Mean Marrow Dose (MMD) or Bone Marrow Dose
3.Gonad Dose / Genetically Significant Dose (GSD)

Entrance Skin Exposure (ESE)
•Often referred to as patient dose or patient skin dose
•TLDs most often used as patient monitors
–Lithium fluoride (Z=8.2) responds
similar to soft tissue (Z=7.4)
–Packs of 3-10 are taped to patient’s skin in centre of X-ray field
–Measurements accurate within 5% (Bushong)
Bone Marrow Dose
•Defined as the “average radiation dose to the entire active bone marrow”
•What is the MMD if 50% of active bone marrow is in the primary beam that received an average dose of 0.16 mGy
•Answer: MMD = 0.08 mGy
–0.16 mGy x 0.50 = 0.08 mGy
Gonad Dose
•The protection of gonads in important is diagnostic radiology as genetic effects may result from exposure to ionizing radiation
•Gonad protection results in low gonad dose
•Sherer; Table 1-8 page 21

Genetically Significant Dose
•Low gonad dose received by individuals, however when applied to an entire population the dose is significant
•A weighted-average  gonad dose, takes into account persons irradiated and those who are not, and averages the results
•Estimated through large-scale epidemiologic studies

Embryo-Fetus Dose
•Irradiation of an unknown pregnancy
•Request for radiation dose received by embryo-fetus
–Detail particulars  about the x-ray examination
–Details to radiation protection officer (RPO) or medical physicist who will determine the ~ absorbed equivalent dose to embryo-fetus
Section 6.2
Patient dose in mammography
•Used to detect breast cancer that is not palpable in physical examinations
•Screen-film and digital mammography
–4:1 or 5:1 ratio grids used to improve contrast, but also increases patient dose
–Consider the glandular dose which is equal to ~ 15% of the ESE
–Glandular dose per view is ~ 1.2 – 3 mGy
Calculating Glandular Dose
•Mammography uses low energy levels in the range of 23 – 28 kVp resulting in high ESE
•Glandular tissue dose is an important consideration as this is the tissue where breast cancer begins
•What is the glandular dose if the ESE measures 800 mR on a CC projection?
•Answer: 120 mR per exposure
–800 mR x 0.15 = 120 mR

Patient Dose in Mammography
•Dose reduction in mammography
–Limit the number of projections/views
–Digital mammography should result in a lower glandular dose versus film-screen
•Safety Code 33
–Handout  Mammography Guidelines according to Safety Code 33

Patient Dose in CT
1. Dose distribution is nearly uniform as CT results in a rotational acquisition  as compared to conventional radiography and fluoroscopy where the entrance exposure dose is much greater than the exit dose
2. To achieve high contrast resolution in CT the radiation dose per slice volume is higher because the techniques are higher as compared to conventional radiography
3. Finely collimated beam of X-rays results in a decrease in scatter radiation and improved contrast resolution
– Ideally, a well defined  volume of tissue is irradiated for each image
– Reality is blurring of the sharp boundary, this is called penumbra
-Result, multiple-scan CT imaging results in lower patient dose versus conventional single-scan CT (step-and-shoot)

•Ratio between patient couch  movement (0.5:1) and x-ray beam width (0.5:1 )
•Expressed as a ratio, 0.5:1, 1:1, 1.5:1, or 2:1
–A pitch of 0.5:1 results in overlapping images and higher patient dose
–A pitch of 2:1 results in extended imaging and lower patient dose
Dose Measurement
•Compton scattering contributes significantly to patient dose in CT
–Tissue “slices” receive both primary and scattered radiation
•Multiple scan average dose (MSAD) is the standard for determining radiation dose in CT
–Incorporates  dose received by scattered radiation from adjacent  slices
Multiple Scan Average Dose (MSAD)
•Defined as the average dose, at a particular depth from the surface, resulting from a large series of CT slices
•An estimate of MSAD can be determined with a single scan by measuring the CT dose index (CTDI)

Section 6.4
Guideline for reduction of dose to sensitive tissues
•SC 35 “Guidelines for Reduction of Dose to Sensitive Tissues” have already been discussed in Unit 4 Minimizing Radiation Exposure to Patients
–SC35: Section A 3.4 (P. 15)
Section 6.5
Diagnostic Reference Levels
3.5.1 Introduction
–Doses for medical diagnostic procedures can vary widely between equipment and facilities.
–Using surface air kerma limits is not an acceptable value to use in diagnostic radiology
•Reason: The air kerma dose limits are set at high values therefore any doses greater than the dose limit are unacceptable values; not optimizing patient doses
–DRLs are guidelines to optimize  doses during procedures
–DRLs are based on typical examinations of standardized patient or phantom  sizes
3.5.2 Application
–Common procedures performed on adults and children require DLR measurements
–DRL measurements may be performed either with a phantom (preferred) or using patients (not allowed for pediatric DRLs)
•General duty examinations (CXR, L-spine); phantom required to be 23 cm thickness
•CT; DLRs based on the weighted CT Dose Index (CTDIW)
•Patient; only done on patients whose individual weight is 70 +/- 20 kg; minimum sample size of 10 patients
–Entrance surface doses for establishing DRLs may be measured using;
•TLDs placed on the patient
•Dose area product (DAP) meter
•Information retrieved from the RIS
–DRL values should be reviewed annually
•Radiation Protection Services, Department of Medical Physics, Cancer Care Manitoba
–DLR values must not be used for comparison with individual patients. Values should only be compared with the average of a collection of patients of a specific weight.
–To evaluate conformity  evaluations should be done at the X-ray room level or X-ray equipment type, i.e. mobiles, CT
•The mean patient dose for an examination is then compared to the DRL for the examination
•Causes of significant and consistent values exceeding the DRLs will require an investigation
3.5.3 Recommended DRL Values (P. 16 – 17)
•Table 1: DRLs for radiographic procedures performed on adults
•Table 2: DRLs for radiographic procedures performed on a five-year-old child
•Table 3: DRLs for radioscopic procedures
•Table 4: DRLs for CT procedures

Table 1: representative DRLs for radiographic procedures performed on adults (IPEM 2004), (IAEA 1996)
Examination  Entrance Surface Dose (mGy)
Chest (PA)  0.2 – 0.3
Chest (LAT)  0.7 – 1.5
Thoracic Spine (AP)  5 – 8
Thoracic Spine (LAT)  7 – 10
Lumbar Spine (AP)  7 – 10
Lumbar Spine (LAT)  15 – 30
Abdomen (AP)  7 – 15
Pelvis (AP)  5 – 10
Skull (AP)  4 – 5
Skull (LAT)  2 – 3
SC35 P. 17

“Radiation Exposure in X-ray Examinations”
•This article compares doses received from various radiological examinations and natural background sources
•These comparisons help to put doses into perspective; this will assist you when discussing exposure to ionizing radiation with your patient
•Other topics discussed in the article include;
–X-ray safety, X-rays over your lifetime, Pregnancy and X-rays, and Radiation dose from interventional radiology procedures
•Your patient may want to discuss any of these topics with their technologist
•Review this article to facilitate class discussion

The End

Radiation Protection Book,
1. Interdiction to Radiation Protection
X-rays are a form of ionizing radiation. When passing through matter, ionizing radiation produces positively and negatively charged particles (ions). The production of these ions is the event that may cause injury in normal biologic tissue.

BOX 1-1 Consequences of Ionization in Human Cells
• Creation of unstable atoms
• Production of free electrons
• Production of low-energy x-ray photons
• Creation of reactive free radicals capable of producing substances poisonous to the cell
• Creation of new biologic molecules detrimental to the living cell
• Injury to the cell that may manifest itself as abnormal function or loss of function

Effective radiation protection
Diagnostic imaging professionals have an ongoing responsibility to ensure radiation safety during all medical radiation procedures. They fulfill  this obligation  by adhering to an established radiation protection program. Radiation protection may be defined simply as effective measures employed by radiation workers to safeguard patients, personnel, and the general public from unnecessary exposure to ionizing radiation. Effective protective measures take into consideration both human and environmental physical determinants, technical elements, and procedural factors. They consist of tools and techniques used to minimize radiation exposure while producing optimal-quality diagnostic images. Unfortunately, there is not just one unique set or system of units. Rather, there are currently in existence three such unit systems, and each one has a significant area of usage.

Need to Safeguard against Significant and Continuing Radiation Exposure
Biologic Effects
The need for safeguarding against significant and continuing radiation exposure is based on evidence of harmful biologic effects. Various methods of radiation protection may be applied to ensure safety for persons employed in radiation industries, including medicine, and for the population at large. In medicine, when radiation safety principles are correctly applied during imaging procedures, the energy deposited in living tissue by the radiation can be limited, thereby reducing the potential for adverse biologic effects.

Benefit versus Risk
Radiation exposure should always be kept at the lowest possible level for the general public. However, when illness or injury occurs or when a specific imaging procedure for health screening purposes is prudent, a patient may elect to assume the relatively small risk of exposure to ionizing radiation to obtain essential diagnostic medical information. A prime example of such a voluntary assumption  of risk occurs when women elect to undergo screening mammography to detect breast cancer in its early stages. Because mammography continues to be the most effective tool for diagnosing breast cancer early, when the disease can best be treated, its use contributes significantly to improving the quality of life for women. When ionizing radiation is used in this fashion for the welfare of the patient, the directly realized benefits of the exposure to this radiant energy far outweigh any slight risk of inducing a radiogenic malignancy or any genetic defects.
Diagnostic Efficacy
Diagnostic efficacy is the degree to which the diagnostic study accurately reveals the presence or absence of disease in the patient. It is maximized when essential images are produced under recommended radiation protection guidelines. Efficacy is a vital part of radiation protection in the healing arts. It provides the basis for determining whether an imaging procedure or practice is justified. The referring physician carries the responsibility for determining this medical necessity for the patient. After ordering an x-ray examination or procedure, the referring physician must accept basic responsibility for protecting the patient from nonuseful radiation exposure. The physician exercises this responsibility by relying on qualified imaging personnel. As health care professionals, radiographers accept a portion of the responsibility for patient welfare by providing high-quality imaging services. The radiographer and participating radiologist share in keeping patient medical radiation exposure at the lowest level possible. In this way imaging professionals help ensure that both occupational and nonoccupational doses remain well below maximum allowable levels—that is, the upper boundary doses of ionizing radiation for which there is a negligible risk of bodily injury or genetic damage. This can best be accomplished  by using the smallest radiation exposure that will produce useful images and by producing optimal images with the first exposure. Repeated examinations made necessary by technical error or carelessness must be avoided because they significantly increase radiation exposure for both the patient and the radiation worker.
BOX 1-2 Achievement of Diagnostic Efficacy
Imaging procedure or practice justified by referring physician
→ Minimal radiation exposure
→ Optimal image(s) produced
→ Presence or absence of disease revealed
= Diagnostic efficacy

Concepts of Radiologic Practice
ALARA is an acronym for as low as reasonably achievable. This term is synonymous with the term optimization for radiation protection (ORP). The intention  behind these concepts of radiologic practice is to keep radiation exposure and consequent dose to the lowest possible level. In addition, because there are no established dose limits for the amount of radiation that patients may receive for individual imaging procedures, the ALARA philosophy should be established and maintained and must show that we have considered reasonable actions that will reduce patient and personnel dose below required limits. Radiation-induced cancer does not have a fixed threshold—that is, a dose level below which individuals would have no chance of developing this disease. Therefore, because it appears that no safe dose levels exist for radiation-induced malignant disease, radiation exposure should always be kept ALARA for all medical imaging procedures, and ALARA should serve as a guide to radiographers and radiologists for the selection of technical exposure factors.
For many radiation regulatory agencies the ALARA principle provides a method that can be used to compare the amount of radiation that various health care facilities in a particular area use for specific imaging procedures. For example, if patients in that location were receiving on average approximately the same entrance skin exposure (ESE) for a specific imaging procedure in every health care facility in that same area, then that ESE would represent the radiation exposure and consequent dose that is reasonably achieved within that specific location. However, if one of the health care facilities in this same area began giving its patients higher-radiation ESEs and subsequent doses, that institution would no longer be in compliance  with ALARA standards. The noncompliant facility would have to take the necessary action to bring the ESE values and subsequent doses back to a level that would comply with regulatory standards.
Responsibility for Maintaining ALARA in the Medical Industry
Both employers of radiation workers and the workers themselves have a responsibility for radiation safety in the medical industry. For the welfare of patients and the workers, facilities providing imaging services must have an effective radiation safety program. This requires a firm commitment  to radiation safety by all participants. It is the responsibility of the employer to provide the necessary resources and appropriate environment in which to execute an ALARA program. A written policy statement describing this program and identifying the commitment of management to keeping all radiation exposure ALARA must be available to all employees in the workplace. To determine how radiation exposure in the workplace might be lowered, management should perform periodic exposure audits . Radiation workers with appropriate education and work experience must function with awareness of rules governing the work situation. When radiation is safely and prudently  used in the imaging of patients, the benefit of the exposure can be maximized while the potential risk of biologic damage is minimized.
BOX 1-3 Responsibilities for an Effective Radiation Safety Program
Employers’ Responsibilities
• Implement and maintain an effective radiation safety program in which to execute  ALARA by providing the following:
• Necessary resources
• Appropriate environment for ALARA program
• Make a written policy statement describing the ALARA program and identifying the commitment of management to keep all radiation exposure ALARA available to all employees in the workplace.
• Perform periodic exposure audits to determine how to lower radiation exposure in the workplace.
Radiation Workers’ Responsibilities
• Be aware of rules governing the workplace.
• Perform duties consistent with ALARA.

Educating Patients about Imaging Procedures
Patients not only should be made aware of what a specific procedure involves and what type of cooperation is required, but also they must be informed of what needs to be done, if anything, as a follow-up to their examination. Through appropriate and effective communication, patients can be made to feel that they are active participants in their own health care.
Risk of Imaging Procedure versus Potential Benefit
In general terms, risk can be defined as the probability of injury, ailment , or death resulting from an activity. In the medical industry with reference to the radiation sciences, risk is the possibility of inducing a radiogenic cancer or genetic defect after irradiation. Typically, people are more willing to accept a risk if they perceive that the potential benefit to be obtained is greater than the risk involved. Regarding exposure to ionizing radiation, patients who have an understanding of the medical benefit of an imaging procedure because they received factual information about the study before having the examination are more likely to overcome any radiation phobia and be willing to assume a small risk of possible biologic damage. The information, coupled with better design of medical imaging equipment and improved radiation safety standards, has greatly reduced risk from imaging procedures for both patients and radiographers. When radiographers use their intelligence and knowledge to answer patient questions about the risk of radiation exposure honestly, they can do much to alleviate any patient apprehension  and fears during a routine radiologic examination.

Background Equivalent Radiation Time
Another way radiographers can improve understanding and reduce fear and anxiety for the patient is to use the background equivalent radiation time (BERT). This method compares the amount of radiation received, for example, from a patient’s chest x-ray examination or from radiography of any other part of the anatomy, with natural background radiation received over a given period of time such as days, weeks, months, or years. BERT is based on an annual U.S. population exposure of approximately 3 millisieverts per year (300 millirems per year). Using the BERT method in this context has the following advantages:
• BERT does not imply  radiation risk; it is simply a means for comparison.
• BERT emphasizes that radiation is an innate  part of our environment.
• The answer given in terms of BERT is easy for the patient to comprehend .

Types of Radiation
In the simplest terms, energy is the ability to do work—that is, to move an object against resistance. Radiation refers to energy that passes from one location to another and can have many manifestations . By this definition, there are many types of radiation. One example is mechanical vibration of materials. Such mechanical vibrations can travel through the air or other materials to interact with structures in the human ear and produce the sensation we call sound. Ultrasound is the mechanical vibration of a material in which the rate of vibration does not stimulate the human ear sensors and therefore is beyond the range of human hearing. Another example of radiation is the electromagnetic wave. Radio waves, microwaves, visible light, and x-rays are all representative of this form of radiation. In electromagnetic waves, electric and magnetic fields fluctuate rapidly as they travel through space. A limited range of frequencies of this fluctuation is interpreted by its interaction with the human system as visible light. Within this range, small variations in frequency—the number of cycles or wavelengths of a simple harmonic motion per unit of time—are interpreted as different colors. However, frequencies both above and below the visible range exist and have many uses. Electromagnetic waves are also characterized by their wavelength, which is simply the physical distance between successive maximum values of electric and magnetic fields.
Electromagnetic radiation appears to have a dual nature, referred to as wave-particle duality. This means that this form of radiation can travel through space in the form of a wave but can interact with matter as a particle of energy. For this reason x-rays may be described as both waves and particles.

The Electromagnetic Spectrum
The full range of frequencies and wavelengths of electromagnetic waves is known as the electromagnetic spectrum. Table 1-2 shows the electromagnetic spectrum in terms of frequency (given in units of hertz [Hz] or crests, or cycles per second), wavelength (in meters), and energy (specified in electron volts [eV], a unit of energy equal to the quantity of kinetic energy an electron acquires as it moves through a potential difference of 1 volt). Each frequency within the spectrum has a characteristic wavelength and energy. Some of the practical uses of these different frequency ranges are listed. Note that higher frequencies are associated with shorter wavelengths and higher energies; therefore as the wavelength ranges from largest to smallest, frequencies and energy cover the corresponding smallest to largest ranges.

Ionizing and Nonionizing Radiation
For our purposes in the study of radiation protection, the electromagnetic spectrum can be divided into two parts: ionizing and nonionizing. Of the entire span of electromagnetic radiations included in the electromagnetic spectrum, only x-rays, gamma rays, and high-energy ultraviolet radiation (energy above 10 eV) are classified as ionizing radiations. Low-energy ultraviolet radiation, visible light, infrared rays, microwaves, and radio waves are considered to be nonionizing because they do not have sufficient kinetic energy to eject electrons from the atom. If electromagnetic radiation is of a high enough frequency, it can transfer sufficient energy to some orbital electrons to remove them from the atoms to which they were attached. This process, called ionization, is the foundation of the interactions of x-rays with human tissue. It makes them valuable for creating images but has the undesirable result of potentially producing some damage in the biologic material. The amount of energy transferred to electrons by ionizing radiation is the basis of the concept of radiation dose. Thus, a radiation quantity such as equivalent dose, described in the following section, applies only to ionizing types of radiation. Equivalent dose cannot be used to specify the amount of energy imparted  to a potato in a microwave oven or to a sunbather on the beach because no ionization is produced by microwaves or sunlight.

1-4 Calculation of the Wavelength and Energy of Electromagnetic Radiation
The speed of light (c), wavelength (λ), and frequency (ν), are related by the following equation:
c = λν
where c = 3 × 108 m/sec.
Therefore if the frequency of an electromagnetic wave is known, the wavelength may be calculated as follows:
λ = c/ν
The energy (in electron volts, eV) of an electromagnetic wave may be calculated using the frequency (ν) and Planck’s constant (h) as follows:
E = hν
where h = 4.14 × 10−15 eV-sec
Particulate  Radiation
In addition to electromagnetic radiation, there is another category of ionizing radiation called particulate radiation. This form of radiation includes alpha particles, beta particles, neutrons, and protons. All of these are subatomic particles that are ejected from atoms at very high speeds. They possess sufficient kinetic energy to be capable of causing ionization by direct atomic collision . However, no ionization occurs when the subatomic particles are at rest.
Alpha particles are emitted from nuclei of very heavy elements such as uranium and plutonium during the process of radioactive decay. Radioactive decay is a naturally occurring process in which unstable nuclei relieve  that instability  by various types of nuclear spontaneous emissions, one of which is the emission of charged particles. Alpha particles each contain two protons and two neutrons. They are simply helium nuclei (i.e., helium atoms minus their electrons). Alpha particles have a large mass (approximately four times the mass of a hydrogen atom) and a positive charge twice that of an electron. This permits them to have the potential of transferring very substantial kinetic energy to orbital electrons of other atoms.
Particulate radiations vary in their ability to penetrate matter. Compared with beta particles, which are just fast electrons, alpha particles are less penetrating. Because alpha particles lose energy quickly as they travel a short distance in biologic matter (i.e., into the superficial layers of the skin), they are considered virtually harmless  as an external source of radiation. A piece of ordinary paper can absorb them or function as a shield. However, as an internal source of radiation, the reverse is true. If emitted from a radioisotope  deposited in the body, for example, in the lungs, alpha particles can be absorbed in the relatively radiosensitive epithelial tissue and can be very damaging to that tissue. It is in a way analogous to what a bowling  ball does to a set of pins .
Beta particles, also known as beta rays, are identical to high-speed electrons except for their origin. Electrons originate in atomic shells, whereas beta particles, like alpha particles, are emitted from the nuclei of radioactive atoms, but radioactive atoms that relieve their instability in a different fashion. Beta particles are 8000 times lighter than alpha particles and have only one unit of electrical charge (−1) as compared with the alpha’s two units of electrical charge (+2). These attributes mean that beta particles will not interact as strongly with their surroundings as alpha particles do. Therefore they are capable of penetrating biologic matter to a greater depth than alpha particles with far less ionization along their paths. It should be noted that some high-speed electrons are not beta radiation. These are produced in a radiation oncology treatment machine called a linear accelerator. These electrons are most often used to treat superficial skin lesions in small areas and to deliver radiation boost treatments to breast tumors at tissue depths typically not exceeding 5 to 6 cm. As previously stated, alpha rays can be absorbed by a piece of ordinary paper because they interact so readily with matter, losing their kinetic energy quite rapidly as a consequence. Beta rays, however, with a lesser probability of interaction, can penetrate matter more deeply and therefore cannot be stopped by an ordinary piece of paper. Either a thick block of wood or a 1-mm–thick lead shield would be required to absorb them.
Protons are positively charged components of an atom. They have a very small mass, which, however, exceeds that of an electron by a factor of 1800. The number of protons in the nucleus of an atom constitutes its atomic number, or “Z” number.
Neutrons are the electrically neutral components of an atom and have approximately the same mass as a proton. If two atoms have the same number of protons but a different number of neutrons in their nuclei, they are referred to as isotopes.

Radiation Dose Specification: Equivalent Dose
Equivalent dose (EqD) is a radiation quantity used for radiation protection purposes when a person receives exposure from various types of ionizing radiation. This quantity attempts to numerically specify the differences in biologic harm that are produced by different types of radiation. EqD enables  the calculation of the effective dose (EfD). EfD takes into account the dose for all types of ionizing radiation (e.g., alpha, beta, gamma, x-ray) to irradiated organs or tissues in the human body (skin, gonadal tissue, thyroid, etc.). By including specific weighting factors for each of those parts of the body mentioned, EfD takes into account the chance of each of those body parts for developing a radiation-induced cancer (or in the case of the reproductive organs, the risk of genetic damage [radiation damage to generations yet unborn]). Because EfD takes into account all of the organ weighting factors, it represents the whole body dose that would give an equivalent biologic response. In the International System of Units (SI), the unit of EqD is the sievert (Sv). In the traditional system, the corresponding unit is the rem. One sievert equals 100 rem. Both occupational and nonoccupational dose limits are expressed as EfD and may be stated in sieverts (rem). EfD, EqD, and other units of dosimetry.

Biologic Damage Potential
Ionizing radiation produces biologic damage while penetrating body tissues primarily by ejecting  electrons from the atoms composing  the tissues. Destructive radiation interaction at the atomic level results in molecular change, and this in turn can cause cellular damage, leading to abnormal cell function or loss of cell function. If excessive cellular damage occurs, the living organism exhibits  genetic or somatic changes such as mutations, cataracts, and leukemia. Changes in blood count are a classic example of organic damage that results from significant exposure to ionizing radiation. An EqD as low as 0.25 Sv (25 rem) delivered to the whole body may cause a decrease within a few days in the number of lymphocytes (white blood cells that defend the body against foreign invaders  by producing antibodies to combat disease) in the blood. Table 1-3 provides some basic information on the known biologic effects of different radiation EqDs that result when radiation exposures are delivered to the whole body over a time period of less than a few hours (acute exposures). Because of the potential for biologic damage from different radiation EqDs to the whole body, the use of ionizing radiation should be limited whenever possible.

TABLE 1-3 Radiation Equivalent Dose (EqD) and Subsequent Biologic Effects Resulting from Acute Whole Body Exposures
Radiation EqD
Sv rem Subsequent Biologic Effects
0.25 25 Blood changes (e.g., measurable hematologic depression, decreases in the number of lymphocytes present in the circulating blood)
Adapted from Radiologic health, unit 4, slide 17, Denver, Multi-Media Publishing (slide program).
Sources of Radiation
Sources of ionizing radiation may be natural or manmade (artificial). However, significant changes have occurred in the amount of radiation exposure to this population from medical imaging procedures. This increase in exposure results from the increased use of imaging modalities such as computed tomography (CT) and cardiac nuclear medicine examinations.

Natural Radiation
Ionizing radiation from environmental sources is called natural background radiation and has the following three components:
• Terrestrial radiation from radioactive materials in the crust of the earth
• Cosmic radiation from the sun (solar) and beyond the solar system (galactic)
• Internal from radionuclides, radioactive atoms that make up a small percentage of the body’s tissue
If radiation from any of these natural sources becomes increased because of accidental or deliberate  human actions such as mining, the sources are termed enhanced  natural sources.

Terrestrial Radiation
Long-lived radioactive elements such as uranium-238, radium-226, and thorium-232 that emit densely  ionizing radiations are present in variable quantities in the crust of the earth. These sources of ionizing radiation are classified as terrestrial radiation. The quantity of terrestrial radiation present in any area depends on the composition of the soil or rocks in that geographic area. In accordance with information contained in NCRP, approximately 55% of the gross  common exposure of human beings to natural background radiation came from radon. Radon, the first decay product of radium, is a colorless, odorless, heavy radioactive gas that along with its decay products, polonium-218 and polonium-214 (solid form), is always present to some degree in the air. Because it is a gas, radon can percolate  up through the soil. It enters buildings through cracks or holes in their frameworks .

Cosmic Radiation
Cosmic rays are of extraterrestrial origin and result from nuclear interactions that have taken place in the sun and other stars. The intensity of cosmic rays varies with altitude  relative to the earth’s surface. The greatest intensity occurs at high altitudes, and the lowest intensity occurs at sea level. The earth’s atmosphere and magnetic field help shield it from cosmic rays. The shielding is diminished  at higher elevation where less atmosphere separates the earth from cosmic rays. Cosmic radiations consist predominantly of high-energy protons; as a result of interactions with molecules in the earth’s atmosphere, these protons may be accompanied by alpha particles, atomic nuclei, mesons, gamma rays, and high-energy electrons. These other forms of radiation are collectively referred to as secondary cosmic radiation. The gamma rays among them are energetic enough to penetrate several meters of lead.

Terrestrial and Internal Radiation
The tissues of the human body contain many naturally existing radionuclides  that have been ingested in minute quantities from various foods or inhaled as particles in the air. A radionuclide is an unstable nucleus that emits one or more forms of ionizing radiation to achieve greater stability. These forms of ionizing radiation may include alpha particles (helium nuclei), beta particles (electrons), and gamma rays (similar to x-rays, but usually of higher energy, in the range of a million electron volts [MeV]). Certain types of radioactive decay also affect the distribution of electrons around the atom, resulting in the emission of x-rays. Potassium-40 (40K), carbon-14 (14C), hydrogen-3, and strontium-90 are examples of radioactive nuclides that exist in small quantities within the body. Radionuclides in the soil and air also add to the human radiation dose burden.

Manmade (Artificial) Radiation
Ionizing radiation created by humans for various uses is classified as manmade, or artificial, radiation. Sources of artificial ionizing radiation include the following:
• Consumer products containing radioactive material
• Air travel
• Nuclear fuel for generation of power
• Atmospheric fallout from nuclear weapons testing
• Nuclear power plant accidents
• Medical radiation

Consumer Products Containing Radioactive Material
Consumer products containing radioactive material include airport surveillance  systems; early televisions; electron microscopes; shoe-fitting fluoroscopes used in the early 1950s; ionization-type smoke detector alarms; phonograph record static eliminators; some timepieces ; and video display terminals that use cathode-ray tubes. These products contribute a small fraction of the total average EqD to each member of the general population.

Air Travel
The normal use of the airplane at high elevations brings many humans in closer contact with high-energy extraterrestrial radiation (e.g., cosmic radiation) and consequently increases exposure. A flight on a typical commercial airliner results in an EqD rate of 0.005 to 0.01 mSv/hr (0.5 to 1 mrem/hr).
Sunspots are dark spots that occasionally appear on the surface of the sun. They indicate regions of increased electromagnetic field activity and are sometimes responsible for ejecting particulate radiation into space. This radiation normally constitutes a small fraction of our dose from cosmic radiation here on earth. However, the solar contribution to the cosmic ray background increases during periods of high sunspot  activity.
If a person spends 10 hours flying aboard  a commercial aircraft during a period of normal sunspot activity, that individual will receive a radiation EqD that is about equal to the dose received from one chest x-ray examination. During a solar flare , this dose can be 10 to as much as 100 times higher.

Nuclear Fuel for Generation of Power
Nuclear power plants that produce nuclear fuel for the generation of power do not contribute significantly to the annual EqD.. As of 1987, the nuclear fuel cycle contributed approximately 0.0001% to the total average annual EqD for persons living in the United States.

Atmospheric Fallout from Nuclear Weapons Testing
An accurate estimate of the total annual EqD from fallout cannot be made because actual radiation measurements do not exist. The dose commitment  (the dose that may ultimately be delivered from a given intake of radionuclide) 10 may be estimated by using a series of approximations and simplistic models that are subject to considerable speculation . The actual radiation dose to the global population from atmospheric fallout from nuclear weapons testing is not received all at once. It is instead delivered over a period of years at changing dose rates. The changes in the dose rates depend on factors such as characteristics of the fallout field and the elapsed time since the test occurred. No atmospheric nuclear testing has occurred since 1980.
As of 1987, when spread over the inhabitants  of the United States, fallout from nuclear weapons tests sources contributed less than 0.0116 mSv (1.16 mrem) annually to the EqD of each person. This annual EqD was considered to have a negligible  impact on the U.S. population.

Nuclear Power Plant Accidents
Examples of two nuclear power plant accidents are addressed in the discussions that follow.

Three Mile Island Unit 2
On March 28, 1979, the Three Mile Island Unit 2 (TMI-2) pressurized water reactor, situated on an island in the Susquehanna River, underwent a loss of coolant that resulted in severe overheating of the radioactive reactor core. Consequently, a significant melting of the core occurred. The U.S. Department of Energy estimated that about 40% of the material in the TMI-2 nuclear reactor core reached a molten state. Approximately 15% of the melted uranium dioxide fuel of the core actually flowed through the undamaged portions of the core and settled on the bottom of the reactor vessel. This melted material in the nuclear reactor core and bottom of the reactor vessel formed crusts  on its outside surfaces and in time cooled to resolidified  debris . Although significant melting of the core and flowing of the molten radioactive material into intact  portions of the reactor vessel occurred, fortunately no “melt-through” of the reactor vessel resulted. The accident did, however, result in the destruction of the reactor.

An explosion at a nuclear power plant in Chernobyl on April 26, 1986 resulted in the release of a number of radioactive nuclides, including 46 megacuries of 131I, 136 megacuries of xenon radioisotopes, and 2.3 megacuries of cesium-137 (137Cs). This is far more than 1 million times the amount of radioactive material released at TMI or “30 to 40 times as much radioactivity as the Hiroshima and Nagasaki atomic bombs combined in 1945.” More than 200 people working at the Chernobyl plant received a whole-body EqD exceeding 1 Sv (100 rem). More than two-dozen workers died as a result of explosion-related injuries and the effects of receiving doses greater than 4 Sv (400 rem). The average EqD to the approximately quarter of a million individuals living within 200 miles of the reactor was 0.2 Sv (20 rem), with thyroid doses (from drinking milk containing radioactive iodine) in some individuals exceeding several sieverts. Adverse health effects from radiation exposure are expected to occur for many years as a consequence of the total collective EqD received by the affected population, and “the number of people who could eventually die as a result of the Chernobyl accident is highly controversial.”

Medical Radiation
Medical radiation exposure results from the use of diagnostic x-ray machines and radiopharmaceuticals in medicine. Diagnostic medical x-ray and nuclear medicine procedures are the two largest sources of artificial radiation, collectively accounting for 15% of the total average EfD of the U.S. population as of 1987. These two types of medical radiation accounted for about 0.54 mSv (54 mrem) of the average annual individual EfD of ionizing radiation at that time. The total average annual EfD from manmade and natural radiation, including radon, was 3.6 mSv (360 mrem). Although the amount of natural background radiation remains fairly constant from year to year, the frequency of exposure to manmade radiation in medical applications is rapidly increasing among all age groups in the United States for a number of reasons. Because of medicolegal considerations, physicians in general are relying more on radiologic diagnoses to assist them in patient care. Greater accuracy in radiologic diagnosis resulting from educational and technologic improvements makes this increased use understandable. However, to reduce the possibility of the occurrence of genetic damage in future generations, this increase in frequency of radiation exposure in medicine must be counterbalanced  by limiting the amount of patient exposure in individual imaging procedures. This can best be accomplished through efficient application of radiation protection measures on the part of the radiographer. Also, it is desirable to limit the widespread substitution by many emergency department facilities of unnecessary CT scans for simple chest x-ray studies.
Because of the large variety of radiologic equipment and differences in imaging procedures and in individual radiologist and radiographer technical skills, the patient dose for each examination varies according to the facility providing imaging services. The amount of radiation received by a patient may be indicated in terms of ESE and glandular dose, bone marrow dose, and gonadal dose. In pregnant women, fetal dose also may be estimated.

New Data on Medical Radiation Exposure
In NCRP Report No. 93, medical radiation was estimated to contribute 0.54 mSv to manmade background radiation. In 2006 that number had increased to 3.0 mSv, an increase of more than a factor of five. Medical use now makes up 48% of total background radiation. The main reason for the increase is increased usage of CT. With the advent  of multislice spiral CT, the utility of this imaging modality in areas such as emergency medicine has increased dramatically. In 1980, use of CT resulted in a collective dose of 3700 person-sieverts. In 2006 that number rose to 440,000 person-sieverts.

• Ionizing radiation has both a beneficial and a destructive potential.
• Healthy normal biologic tissue can be injured by ionizing radiation; therefore it is necessary to protect humans against significant and continuous exposure.
• X-rays are a form of ionizing radiation; therefore their use in medicine for the detection of disease and injury requires protective measures.
• To safeguard patients, personnel, and the general public, effective radiation protection measures should always be employed when diagnostic imaging procedures are performed.
• Radiation exposure should always be kept as low as reasonably achievable (ALARA) to minimize the probability of any potential damage to people.
• Referring physicians should justify the need for every radiation procedure and accept basic responsibility for the protection of the patient from ionizing radiation.
• The benefits of exposing patients to ionizing radiation should far outweigh any slight risk of inducing radiogenic cancer or genetic effects after irradiation.
• Radiographers should select the smallest radiation exposure that produces the best radiographic results and should avoid errors that result in repeated radiographic exposures.
• Imaging facilities must have an effective radiation safety program that provides patient protection and patient education.
• Background equivalent radiation time (BERT) is used to compare the amount of radiation a patient receives from a radiologic procedure with natural background radiation received over a specific period of time.
• Ionizing radiation produces electrically charged particles that can cause biologic damage on molecular, cellular, and organic levels in humans.
• Equivalent dose (EqD) is a radiation quantity used for radiation protection purposes when a person receives exposure from various types of ionizing radiation. This quantity attempts to numerically specify the differences in biologic harm that are produced by different types of radiation. EqD enables the calculation of the effective dose (EfD).
• EfD takes into account the dose for all types of ionizing radiation to irradiated organs or tissues in the human body. By including specific weighting factors for each body part, such as skin, gonadal tissue, and thyroid, EfD takes into account the chance of each of these body parts for developing a radiation-induced cancer (or in the case of the reproductive organs, the risk of genetic damage).
• Both occupational and nonoccupational dose limits are expressed as EfD.
• Sievert (Sv) and rem are the units of equivalent dose and effective dose.
• Sources of ionizing radiation may be natural or manmade.
• Natural sources include radioactive materials in the crust of the earth, cosmic rays from the sun and beyond the solar system, internal radiation from radionuclides deposited in humans through natural processes, and terrestrial radiation in the environment.
• Manmade sources include consumer products containing radioactive material, air travel, nuclear fuel, atmospheric fallout from nuclear weapons testing, nuclear power plant accidents, and medical radiation from diagnostic x-ray machines and radiopharmaceuticals in nuclear medicine procedures.

1. A patient may elect to assume the relatively small risk of exposure to ionizing radiation to obtain essential diagnostic medical information when:
1. Illness occurs
2. Injury occurs
3. A specific imaging procedure for health screening purposes is prudent
A. 1 and 2 only
B. 1 and 3 only
C. 2 and 3 only
D. 1, 2, and 3
2. Effective measures employed by radiation workers to safeguard patients, personnel, and the general public from unnecessary exposure to ionizing radiation defines:
A. Diagnostic efficacy
B. Optimization
C. Radiation protection
D. The concept of equivalent dose (EqD)
3. Which of the following is a method that can be used to answer patient questions about the amount of radiation received from a radiographic procedure?
A. ALARA concept
4. The term optimization for radiation protection (ORP) is synonymous with the term:
A. As low as reasonably achievable (ALARA)
B. Background equivalent radiation time (BERT)
C. Equivalent dose (EqD)
D. Diagnostic efficacy (DE)
5. Which of the following are natural sources of ionizing radiation?
A. Medical x-radiation and cosmic radiation
B. Radioactive elements in the crust of the earth and in the human body
C. Radioactive elements in the human body and a diagnostic x-ray machine
D. Radioactive fallout and environs of atomic energy plants
6. An equivalent dose as low as 0.25 Sv (25 rem) delivered to the whole body may cause which of the following within a few days?
A. An increase in the number of lymphocytes in the circulating blood
B. A decrease in the number of lymphocytes in the circulating blood
C. A drop immediately to zero in the lymphocyte count
D. A large increase in the number of platelets
7. The degree to which the diagnostic study accurately reveals the presence or absence of disease in the patient defines which of the following terms?
A. Radiation protection
B. Radiographic pathology
C. Effective diagnosis
D. Diagnostic efficacy
8. Which of the following was the total average annual effective dose from manmade and natural radiation as of 1987?
A. 0.3 mSv (30 mrem) per year
B. 0.6 mSv (60 mrem) per year
C. 1.8 mSv (180 mrem) per year
D. 3.6 mSv (360 mrem) per year
9. An effective radiation safety program requires a firm commitment to radiation safety by:
1. Facilities providing imaging services
2. Radiation workers
3. Patients
A. 1 and 2 only
B. 1 and 3 only
C. 2 and 3 only
D. 1, 2, and 3
10. Which of the following is recognized as the main adverse health effect from the 1986 Chernobyl nuclear power accident?
A. Increase in the incidence of leukemia in adults
B. Increase in the incidence of leukemia in children
C. Increase in the incidence of thyroid cancer in adults
D. Increase in the incidence of thyroid cancer in children and adolescents.



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