Radiation Protection

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Radiation Protection

  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 HISTORY OF RADIATION PROTECTION 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[1] 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 FIGURE 3-1 Wilhelm Conrad Roentgen, the discoverer of x-rays. •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 JUSTIFICATION OF RADIATION EXPOSURE Justification[2] •Benefit vs. Risk •The referring physician has the responsibility to conduct[3] a thorough clinical examination to ensure the benefits of the ordering an x-ray outweigh[4] the potential risk of biologic damage [5] 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[6] 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[7] examination. Relevant[8] 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 GuidelinesPatient related –general (PRG) Annex[9] 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[10] displayed[11] •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 Optimization •ALARA and ALARP •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[12] exposure factors for the body part of interest, ensuring only the area of interest is within the collimated field, etc. Section 1.4 PATIENT PROTECTION AND EDUCATION 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[13] 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[14] 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 BERT •Background Equivalent Radiation Time •A technique that may be used by a technologist to help relay[15] 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 EMR 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                     Natural radiation 1. Terrestrial radiation –Radioactive elements present in crust[16] 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. TABLE 1-4 Average Annual Radiation Equivalent Dose (EqD) for the United States [1987, NCRP] 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[17] from Nuclear Weapons 5.Nuclear power plant accidents 6.Medical radiation Nuclear Power Plant Accidents •Three Mile Island –March 28, 1979 –Pressurized[18] 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[19] 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 EXPOSURE 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 FIGURE 2-3 primary, exit, and attenuated photons. Primary photons (photons 1, 2, 3, and 4) are photons that emerge[20] from the x-ray source. Exit, or image-formation, photons (photons 1 and 2) are photons that pass through the patient being radiographed and reach the radiographic image receptor. Attenuated photons (photons 3 and 4) are photons that have interacted with atoms of the patient’s biologic tissue and been scattered or absorbed such that they do not reach the radiographic image receptor X-ray Interaction with Matter •In the diagnostic range two interactions with matter are predominant[21] –Photoelectric absorption –Compton scattering •The predominance[22] 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[23] 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 unit

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) à exposure 2. rad(rad) à absorbed dose 3. rem(rem) à equivalent & effective dose 4. Curie (Ci) SI Units 1. Air kerma (Gy or Gya) à exposure 2. Gray (Gy or Gyt) à absorbed dose 3. seivert (Sv) à 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. Exposure •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 •Conversions: 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) FIGURE 3-7 Probability[24] of interaction of x-rays when a 5-cm–thick layer of soft tissue or bone is encountered[25]. The probability is greater at lower energies and is greater for bone than soft tissue, particularly at low energies. 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 •Conversions: 1 rad= 1 Gy divided by 100 rad = 0.01 Gy OR 10 mGy Dose Equivalence[26] •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[27] the absorbed dose valu Radiation Weighting[28] Factor (WR) •Chosen for each type and energy of radiation •Selected by national and international scientific advisory[29] bodies (NRCP, ICRP[30]) •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) •Relationship: 1 Sv= 100 rem •Conversions: 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[31] 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) •Relationship: 1 Sv= 100 rem •Conversions: 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 •Characteristics –Lightweight and easy to carry –Durable, ability to withstand normal daily use –Ability to detect both small and large doses consistently[32] and reliably –Withstand[33] sensible[34] 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[35], 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[36] 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[37] a number of different films to known doses of radiation   Control Badge •Included with each batch[38] 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[39] •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[40] 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[41] band –Electrons within this band are free to move providing they maintain a certain[42] 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[43] that is sealed within a light-tight black paper wrapper[44] –Filter material is aluminum, tin[45] and copper –Enables radiation energy discrimination[46] •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[47] 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[48] 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 >[49] 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[50] 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[51] (reading scale) of the eyepiece •Special charging unit –The pocket dosimeter is charged to a predetermined[52] voltage so the quartz fibre indicates a zero reading •The pocket dosimeter is charged causing the moveable quartz fibre to repel[53] 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[54] 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 TLDs •Appearance similar to a film dosimeter •Contains a holder and an insert •Insert consists of an aluminum plaque[55], 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[56] 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 TLDs •The amount of light released (luminescence) is measured with a photomultiplier tube or a photodiode •The intensity of light is plotted[57] 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[58] 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[59] 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[60] 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[61] 3. Epidemiological research 4. Litigation[62] •Report provided for each dosimeter submitted[63] Information on a Personnel Monitoring Report •Group number –Number assigned to Red River College •Date of report •Description[64] of the type of service –TLD service, Quarterly[65], 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[66]. 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 •Anomaly –*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 Introduction •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 –Ionization –Photographic effect –Luminescence –Scintillation[67]   Ionization •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[68], vicinity[69] of NM or therapy patients, outside of protective barriers, and for precise calibration of diagnostic x-ray equipment   Calibration[70] 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[71] (mR), reproducibility and linearity of output etc Proportional Counter •Proportional counters[72] 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[73] 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[74] 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[75] 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[76] 7. Cost effective including maintenance charges Section 2.4 Radiation protection organizations Introduction •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 1.ICRP 2.UNSCEAR 3.NAS/NRC-BEIR 4.RERF ICRPInternational 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[77]. i.e. BEI UNSCEARUnited 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[78] of biological effects among the general population. NAS/NRC-BEIRNational Academy of Sciences/National Research Council on the Biological Effects of Ionizing Radiation •Established in 1963 •Serves to advise agencies and governments of[79] the health effects of radiation exposures •Publishes reports on the most current studies and findings. RERFRadiation Effects Research Foundation •Established:1950’s •Members: Gov’tof Japan •Studies the survivors of atomic bombs at Hiroshima and Nagasaki •Publishes results of studies/research. National Organizations 1.CRPA 2.CNSC 3.RPB-HC CRPACanadian Radiation Protection Association •Established:1982 •Promotes research, scientific study and educational opportunities in radiation protection. CNSCCanadian 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[80] in Canada RPB-HCRadiation Protection Bureau-Health Canada •Provides medical and technical advice •Coordinates Canada’s preparedness[81] for nuclear emergencies •Houses[82] 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 ActRadiation 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: TerminologyMust: 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[83] where applicable[84] 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[85] 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[86] with: –The Manitoba Regulation 341/88R: X-ray Safety Regulation –Public Health Act –RED Act –SC35 Cancer Care Manitoba •Services: –Equipment registrations –Shielding inspections[87] –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[88] by an individual’s germ cells that is transferred to their offspring –Importance of gonad protection Categories of Radiation-Induced Responses 1. Deterministic[89] (nonstochastic) effects 2. Stochastic[90] effects 1. Deterministic Effects •A.k.a nonstochasticeffects –Biologic somatic effects directly related to the radiation dose received –A threshold exists[91] 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[92] – Leukocytopenia[93] – Epilation[94] •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[95] formation –Fibrosis –Organ atrophy –Loss of parenchymal cells –Reduced fertility –Sterility Fig. B, Hypothetical[96] sigmoid (S-shaped, hence[97] nonlinear) threshold curve of radiation dose-response relationship generally employed in radiation therapy to demonstrate high-dose cellular response. 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[98] exposure the probability of sustaining[99] 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[100] 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[101] 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[102] (ova/sperm), mutations may occur with the potential of negative affects on future generations Risk of Cancer Induction •Data used when assessing[103] the risk of cancer induction has been from groups who were exposed to high doses of radiation (i.e. atomic bomb survivors) •Estimates[104] have been extrapolated[105] 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[106]” •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[107] no threshold dose therefore overestimating[108] the risk of injury Objectives[109] of Radiation Protection 1.To prevent any clinically significant radiation-induced deterministic effects –This may be achieved by adhering[110] 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[111] of a linear, nonthreshold relationship between ionizing radiation dose and biological response –There is no known safe level of radiation dose •The premise[112] that ionizing radiation posses both a beneficial and a destructive potential –The benefit of exposure to ionizing radiation must outweigh the potential risk Section 2.6 Radiation exposure risk and dose limits Risk •Any exposure to ionizing radiation has risk associated with that exposure •One way to illustrate[113] that risk is to compare a dose received during a certain diagnostic examination to a comparable dose received by background[114] 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 Research •The BEIR V report adopted[115] the linear no-threshold view based on extrapolated[116] 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[117] 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[118] the BEIR V report which suggests that any amount of radiation has the potential to be harmful •Other studies that have been conducted[119] draw[120] 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 SC35: APPENDIXI SC35: Appendix I •There is no recommended discrimination[121] in dose limits between men and women of reproductive capacity (11 to 55 years) •Technologist-in-training and students must adhere[122] to the dose limits of the general public •Some provincial or territorial jurisdictions[123] may have different dose limits for some radiation workers; consult Appendix V •Once pregnancy has been declared[124] by an RTR, the fetus[125] must be protected from X-ray exposure for the duration of the pregnancy –Effective dose limit of 4 mSv for remainder[126] of the pregnancy from all sources of radiation –Occupational exposure to pregnant RTRs generally arise from scatter radiation. Fetal[127] monitoring may be accomplished by placing a TLD on the surface of the abdome 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[128] 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[129] and maintained for the facility –May delegate[130] 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[131] 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[132] operations •Medical physicist is a HCP with specialized training in medical applications[133] 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[134] –Some jurisdictions authorize[135] 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[136] or available upon request –Information system specialist must ensure confidentiality of patient records 1.7 Repair and Maintenance Personnel (P. 10: 1-7) –Authorized[137] 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 manufacture 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[138] X-ray beam limitation devices Filtration Compensating[139] 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[140] •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 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[141] by the primary beam •SC35; Appendix III P. 63 FIG. 9-5 Protective barriers are lined with lead to protect personnel and the general public from radiation. The primary protective barrier is located perpendicular to the undeflected line of travel of the x-ray beam. The walls that are not in the direct line of travel of the primary beam are called secondary protective barriers, because they are designed to shield against secondary (leakage and scattered) radiation. 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[142] 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[143] (W) •Indicates the operational[144] 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[145] of time •SC35 Table 6: Occupancy Factors (P. 20) •Guide for determining occupancy factor –T=1 indicates areas full occupied by individuals, attended[146] 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[147], staff rest rooms Occupancy factor (T), CS35 P 20 Table 6: Occupancy Factors T=1 Administrative offices and receptionist areas, laboratories, pharmacies and other areas fully occupied by an individual, attended waiting rooms, children’s indoor play areas, adjacent[148] X-ray rooms, image viewing areas, nurses’ stations, X-ray control rooms, living quarters[149]. T=1/2 Rooms used for patient examinations and treatments. T=1/5 Corridors, patient rooms, staff lounges, staff rest rooms. T=1/8 Corridor doors. T=1/20 Public toilets, unattended vending[150] areas, storage rooms, outdoor areas with seating, unattended waiting rooms, patient holding areas. T=1/40 Outdoor areas with only transient[151] pedestrian or vehicular traffic, unattended parking lots, vehicular drop off areas (unattended), attics[152], stairways, unattended elevators, janitor’s closets[153]. Use factor (U) •Defined[154] 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

U=1 Floors of radiation rooms, walls containing a vertical image receptor; any other walls, doors or ceiling areas routinely exposed to the direct radiation beam. U=1/4 Doors and wall areas of radiation rooms not routinely exposed to the direct radiation beam. U=1/16 Ceiling areas of radiation rooms not routinely exposed to the direct radiation beam. Secondary Barrier U=1 The use factor for secondary protective barriers is always taken to be 1. Primary Protective Barrier K= P = maximum permissible[155] 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[156] 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[157] as exposure lines from the isocenter[158] 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[159] acquisition[160] •Scatter radiation for CT scanners has increased with the advent[161] 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 •Immobilization •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[162], reduces anxiety and emotional stress, and enhances the professional image of the MRT –Clear and concise[163] patient instructions maximize cooperation and alleviate[164] patient fears about the procedure •Effective communication will reduce the need for repeat exposures Immobilization •Serves to reduce motion blur on radiographs •Voluntary motion –Reduced through the use of suitable[165] 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 –Breasts •Specific area shielding uses lead or lead-impregnated[166] 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[167] 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[168] a “shadow” in the primary beam –Not suitable during fluoroscopy 3. Shaped contact shields –Made of radiopaque material contoured[169] to fit the male reproductive organs –Placed within a disposable or washable athletic supporters or jockey-style[170] briefs[171] –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 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[172] 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 •Fluoroscopy •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 Laboratory result of changing kVp Beam Filtration •The x-ray beam is polychromatic[173]; 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[174] a dose to skin and shallow[175] tissues •As tube filtration increases; the beam becomes harder; due to fewer low-energy photons FIGURE 10-10 Filtration removes low-energy photons (long-wavelength or “soft” x-rays) from the beam by absorbing them and permits higher-energy photons to pass through. This reduces the amount of radiation that the patient receives. Field Area •Ensuring the collimation field size exposes only the necessary tissue •There is a further[176] benefit; reduction of scatter radiation •A reduction in scatter radiation incident on the image receptor (detector) will improves image contrast Geometry •Increasing the SOD and the SID helps to reduce patient dose •The reduced beam divergence[177] limits the volume of tissue irradiated; thereby reducing the integral[178] 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[179] •Quantum mottle degrades[180] image quality by giving the image a “noisy/blotchy[181]” 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[182] 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[183] 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[184] •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[185] 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[186] 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 •Definition –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[187] 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[188] and correlate[189] 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[190] qualifications to be authorize[191] by legislation[192] to order x-rays •Order an x-ray examination based on professional experience, judgment, and common sense •Give consideration to alternate[193], non x-ray utilizing[194] examinations •Be confident that the procedure will improve the patient diagnosis/treatment sufficiently in comparison[195] 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[196] 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[197] 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[198] 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[199] 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[200] 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[201] 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[202] 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 Fluoroscopy •Has the potential to impart[203] 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[204] –“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 DistanceEquipment must be equipped with a device that limits the focal spot to skin distance

Mobile   Equipment Stationary   Equipment Special   Application[205]
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[206] 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[207] of accumulated patient exposure Methods to Reduce Fluoroscopic Exposure 1. Limit the “beam-on” time by using short bursts[208] of exposure 2. A 5-minute cumulative timer allows a technologist to track[209] 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[210]   Computed Technology (CT) •With the advent[211] of computers it became possible to image the body in “slices” with subsequent[212] images corresponding to a 3D section of the patient versus the traditional 2D projection •The use of CT technology has increased substantially[213] as physicians are relying more on these images to confirm a diagnosis Computed Tomography •Preamble[214]: 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[215] the length of the exposure (e.g. dose) imparted[216] 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[217] 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 (www.imagegently.org) 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[218] 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[219]/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[220] 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[221] 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[222] 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[223] 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[224] 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[225] any apprehension[226] 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[227], care must be taken to minimize the dose to the fetus SC35 (P. 12) 3.1.8 Additional topic in Textbook to Omit[228] •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 Biolog Miscellaneous[229] Considerations •Careful identification of the patient •Elimination[230] of screening[231] examinations that rarely detect pathology •Standing order x-rays, i.e. Pre-op CXR •Frequent screening examinations, i.e. annual[232] 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[233] 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[234]/Compton electron –The amount of energy retained[235] 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 SCATTER RADIATION – The intensity of scatter in various directions is a major factor in planning and executing[236] 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[237] – 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.” SC35: APPENDIX I 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[238] (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[239]-around protective apron with a lead equivalency of 0.5 mm Work Schedule Alteration[240] •Generally an alteration in the technologists work schedule is not required i.e. re-assigned[241] 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 OMIT •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[242] of the pregnancy are compatible[243] 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[244] 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 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[245] during fluoroscopy, mobile radiography, or when the technologist must be in the x-ray roo Protective Apparel •Must be stored on designated racks –If folded or heaped[246] in a corner, cracks can develop •Integrity[247] 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) FIGURE 12-10 The neck and thyroid gland can be protected from radiation exposure through the use of a 0.5 mm lead equivalent protective shield. Protective Gloves •Protective gloves must possess[248] 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) FIGURE 12-11 Eyeglasses protect the lens of the eyes during general fluoroscopy and special procedures. (Shown are glasses with wraparound[249] frames; other styles are also available.) Section 5.3 TECHNICAL CONSIDERATIONS 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[250] 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[251] 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[252] 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[253] principle of time to offer additional radiation protection   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[254] 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[255] 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[256] made to ensure the beam dose not irradiate persons in the vicinity[257] 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[258] discharge unit, after an x-ray irradiation has been made, the residual[259] charge must be fully discharged before the unit is left unattended[260]. 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[261] 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 FIGURE 12-16 Cross-table exposure during use of a C-arm fluoroscope. The exposure rate caused by scatter near the entrance surface of the patient (the x-ray tube side) exceeds[262] the exposure rate caused by scatter near the exit surface of the patient (the image intensifier side). The location of lower potential scatter dose is on the side of the patient away from the x-ray tube (i.e., the image intensifier side). Protection During C-arm Fluoroscopy •Protective apparel for all persons in the vicinity[263] –Manipulation of the equipment into various positions and long fluoroscopy times render[264] 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[265] Techniques – Radiographer •Use of high-quality low-dose fluoroscopy mode •Pulsed beam operation •Collimation •Optimal beam filtration •Removable grids •Variable optical aperture[266] •“Road[267] 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[268] and only when increased visualization is critical and necessary (i.e. deployment[269] of a stent or embolization[270]) Extremity Monitoring •Due to the proximity[271] 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[272] 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[273] 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[274], Bucky slot[275] 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[276] 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[277] 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[278] 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 TABLE 1-8 Typical Gonadal Doses from Various Radiographic Examinations* Genetically Significant Dose •Low gonad dose received by individuals, however when applied to an entire population the dose is significant •A weighted-average[279] 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[280] about the x-ray examination –Details to radiation protection officer (RPO) or medical physicist who will determine the ~ absorbed equivalent dose to embryo-fetus TABLE 1-9 Typical Fetal Dose Factors as a Function of Skin Entrance Exposure 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 Mammography 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[281] Mammography Guidelines according to Safety Code 33 Patient Dose in CT 1. Dose distribution is nearly uniform as CT results in a rotational acquisition[282] 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[283] 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 Pitch[284] •Ratio between patient couch[285] 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[286] dose received by scattered radiation from adjacent[287] 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[288] doses during procedures –DRLs are based on typical examinations of standardized patient or phantom[289] 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[290] 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” •http://www.radiologyinfo.org/en/safety/ •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


4 thoughts on “Radiation Protection

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    March 7, 2018 at 11:34 pm

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