Introduction to Radiation Protection

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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 in black photography paper

–Noticed a plate coated with barium platinocyanideseveral feet away was glowing

–Placed various materials between the Crookes tube and the fluorescing plate

Discovery of X-Rays

–He called the rays “x” Rays, “x” for unknown

–Presented his findings to the scientific community in December 1895

–In 1901 won the first Nobel Prize in Physics

•First x-ray was of his wife’s hand in early 1896

First Reports of Injury

•In the early as 1900s injuries were being observed

–Skin damage (radiodermatitis)

–Loss of hair (epilation)

•In 1904 the first x-ray fatality was reported in the USA, Clarence Madison Dally

•Blood disorders (anemia, leukemia) were being occurring at a higher rate in radiologists

•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

JUSTIFICATION OF RADIATION EXPOSURE

Section 1.2

Justification

•Benefit vs. Risk

•The referring physician has the responsibility to conduct a thorough clinical examination to ensure the benefits of the ordering an x-ray outweigh the potential risk of biologic damage

Guidelines for the Prescription of X-ray Examinations

•“Unnecessary radiation exposure of patients can be significantly reduced by ensuring that all examinations are clinically justified.”

1.The prescription of an x-ray examination of a patient should be based on clinical evaluation of the patientand should be for the purpose of obtaining diagnostic information or patient treatment

2.“X-ray examinations should not be performed if there has been no prior clinical examination of the patient.”

3.“Radiological screening must not be performed unless, it has been proven that the benefit to the individual examined or the population as a whole is sufficient enough to warrant its use.”

SC35 Section A: Responsibilities and Protection; 3.1 Guidelines for the Prescription of X-ray Examinations; P. 12

CAMRT: Risk Management Guidelines

•Patient related –general (PRG) Annex C: Requisition / Requests for Consultation

•No radiographic or imaging examination should be performed by a technologist without:

–A formal request in writing from an authorized referring physician;

–A requisition signed by a person authorized by the facility to order treatment and/or diagnostic examinations; etc.

OPTIMIZATION OF RADIATION EXPOSURE

Section 1.3

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 exposure factors for the body part of interest, ensuring only the area of interest is within the collimated field, etc.

Guidelines for the Prescription of X-ray Examinations

4.It should be determined whether there have been any previous x-ray examinations which would make further examination unnecessary, or allow for the ordering of an abbreviated examination. Relevant previous images or reports should be examined along with a clinical evaluation of the patient.

5.When a patient is transferred from one physician or hospital to another any relevant images, or reports should accompany the patient and should be reviewed by the consulting physician

6.When prescribing a radiological examination, the physician should specify precisely the clinical indications and information required.

SC35 Section A: Responsibilities and Protection; 3.1 Guidelines for the Prescription of X-ray Examinations; P. 12

CAMRT: Risk Management Guidelines

•Staff related –general (SRG) Annex B: Qualifications and Scope of Practice

–It is recommended that in each facility the following are prominently displayed

•CAMRT Code of Ethics

•Scope of Practice for the Profession(s)

–These guidelines are recommended as a way to inform the public of the profession and the profession’s standards, ethics, and limitations. Etc

PATIENT PROTECTION AND EDUCATION

Section 1.4

Effective Communication

•Educate the patient about the procedure they are scheduled to have

•Your expectations of the patient during the procedure

•Provide follow-up instructions

•Effective communication contributes to a positive experience for the patient

Risk of proceeding with the Examination

•Radiation sciences consider risk as the “possibility of inducing a radiogenic cancer or genetic defect after irradiation”

•Informed patients will understand and agree to proceeding with an examination (the benefit) to help determine what is ailing them

•A great deal of knowledge has been gained to better understand biologic effects from medical x-ray exposure

•Advances in equipment design and safety standards reduce the risk of imaging procedures

BERT

•Background Equivalent Radiation Time

•A technique that may be used by a technologist to help relay the concept of “risk” to their patient

•A unit of time (days, weeks, months, years) that is assigned to certain radiographic examinations representing the length of time that would be required to obtain a comparable dose from natural sources

–CXR -BERT = 10 days

RADIATION AND RADIATION SOURCES

Section 1.5

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, rays, particles, particles

–Sufficient kinetic energy to eject an electron from the atom

–Foundation of interaction of x-rays with human tissue

2.Non-ionizing radiation

–Ultraviolet, visible light, infrared, microwaves, radio waves

Sources of Radiation

1.Natural radiation

2.Manmade or artificial radiation

Natural radiation

1.Terrestrial radiation

–Radioactive elements present in crust of the earth (1.98 mSv/year in the U.S.)

2.Cosmic radiation

–Results from nuclear interactions in sun & other stars (0.3 mSv/year in the U.S.)

3.Internal radiation

–Tissues of human body contain many naturally existing radionuclides(0.67 mSv/year in the U.S.)

•Total: 2.95 mSv/year in the U.S.

Manmade or artificial radiation

1.Consumer products containing radioactive material

2.Air travel (0.005 –0.01 mSv/hour)

3.Nuclear power plants

4.Atmospheric fallout from Nuclear Weapons

5.Nuclear power plant accidents

6.Medical radiation

Nuclear Power Plant Accidents

•Three Mile Island –March 28, 1979

–Pressurized water reactor overheated causing overheating of the radioactive core

–About 40% of the reactor core reached the molten state settling on the bottom of the reactor vessel

–Fortunately there was no “melt-through” resulting in only a small quantity of radiation escaping

–No health problems to occupational workers or the 2 million people living within 50 miles of the plant

•Chernobyl –April 26, 1986

–An explosion releasing radioactive nuclides, more than 1 million times the amount released at TMI

–200 workers received whole body doses exceeding 1 Sv

–More than 2 dozen workers received doses greater than 4 Sv

–Average dose received by quarter of a million people within a 200 mile radius was 0.2 Sv

•Fukushima 1 –March 11, 2011

–Japan experienced an earthquake measuring 9.0 on the Richter scale which triggered a tsunami

–The tsunami reached the reactors and disabled the reactors cooling system; an explosion left the reactor cores bare increasing the nuclear radiation levels in the surrounding areas

–On April 20, 2011 Japanese authorities declared the 20 Km evacuation zone be entered only under government supervision

MEDICAL RADIATION EXPOSURE

Section 1.6

Medical Radiation

•Diagnostic imaging and nuclear medicine

•Natural radiation exposure is relatively constant, however medical radiationexposure 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

INTERACTION OF X-RADIATION WITH MATTER

Section 1.7

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;

–kVpdetermines the energy of the x-ray beam

–mAdetermines 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 from the x-ray source. Exit, or image-formation, photons (photons 1 and 2) are photons that pass through the patient being radiographedand 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

–Photoelectric absorption

–Compton scattering

•The predominance of both interactions depends on the incident photon energy

–As photon energy increases the predominant interaction is Compton scattering

–Most interactions occur within the first 5 cm of tissue

Photoelectric Absorption

•Involves the complete absorption of the incident x-ray photon by tissues

•Therefore is the major contributing factor to patient dose

Compton Scattering

•Involves partial energy of the incident x-ray photon is transferred to the tissues

•The x-ray photon is deflected and is now referred to as a scattered photon

•The scattered photon continues to move through tissue along a new path and at a lower energy

•The scattered photon may scatter several more times before being completely absorbed

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