1	Radiation Protection & Associated Regulations Bushberg – Chapter 23 RSNA & AAPM Physics Curriculum: Module 9 Renée Dickinson, MS Medical Physicist, Diagnostic Physics Department of Radiology UW Medicine a copy of this lecture may be found at: http://courses.washington.edu/radxphys/PhysicsCourse.html
2	Module 9: Radiation Protection & Assoicated Regulations Fundamental Knowledge Indentify the sources of background radiation, and describe the magnitude of each source. State the radiation limits to the public and radiation workers (Max Permissible Dose Equivalent limits). Understand the differences among advisory boards, accrediting organizations, and regulatory organizations for radioactive materials and radiation-generating equipment, and recognize their respective roles. Define the principles of time, distance, and shielding in radiation protection. Define ALARA and its application to radiation protection. Identify methods used to monitor occupational exposure. Discuss appropriate equipment used to monitor radiation areas or areas of possible exposure or contamination. Describe the fundamental methods used to determine patient and fetal doses…. Described in detail in 4/15/2010 lecture Explain the basic principles for designing radiation shielding. List the steps in managing radiological emergencies.
3	Module 9: Radiation Protection & Assoicated Regulations Clinical Applications Understand safety considerations for patients and staff, including pregnant staff, in mobile radiography (“portables”). Use your knowledge of radiation effects in planning for and reacting to an emergency that includes the exposure of personnel to radiation. Discuss the contributions of medical sources to the collective effective dose. Define the responsibilities and qualifications of an authorized user (all categories) and the radiation safety officier. Describe the training and experience requirements for using sealed and unsealed sources of radioactive material. Describe the use of personnel radiation protection equipment. Describe the appropriate equipment for wipe tests and contamination surveys. Provide information to the public concerning radon. Provide clinical examples that demonstrate ALARA principles. Discriminate between workers in a public area who are occupationally exposed and those who are treated as members of the general public.
4	Module 9: Radiation Protection & Assoicated Regulations Clinical Problem-Solving Discuss the factors that determine dose to a pregnant person seated next to a patient injected with a radionuclide for a diagnostic or therapeutic procedure. Describe steps used in applying appropriateness criteria. Describe what must be done before administering a radioactive material to a patient. Describe what is required to have a person listed on a facility’s Nuclear Materials License as an Authorized User.
5	Key Points for Radiation Protection Sources of exposure to ionizing radiation Naturally occurring Man-made (technologically) based Personnel dosimetry Radiation protection and exposure control Time, distance and shielding Regulatory agencies and radiation dose limits Occupational limits Non-occupational limits ALARA
6	Review – Radiation Units Exposure, Dose, and Effective Dose What is exposure?? Measurement that describes an x-ray machine output intensity (mR/mAs, mR/min) Only a measure of photon intensity IN AIR Formal definition: the amount of electrical charge (ΔQ) produced by ionizing radiation per mass of air (Δm) [C-kg^-1] Traditional units: Roentgen (R) = 2.58x10^-4C/kg (note: R is still a commonly used unit)
7	Review – Radiation Units (Chapter 3)
8	Sources of Exposure to Ionizing Radiation NCRP Report 93 (published in 1987) NCRP Report 93 – annual exposure to radiation is 3.6 mSv per year – according to NCRP report #160 (published 2009), the medical radiation exposure to US population has increased by nearly 6 times compared to the previous NCRP publication (#93) Medical radiation totaled about 0.53 mSv per year About 3.0 mSv per year from background radiation
9	Sources of Exposure to Ionizing Radiation NCRP Report 160 (published in 2009) NCRP Report 160 – 6.2 mSv per year Medical radiation totals about 3.0 mSv per year – largest contribution is from CT (increased nearly 10-11% annually in the past two decades) & nuclear medicine About 3.1 mSv per year from background radiation
10	Sources of Ionizing Radiation: Naturally Occurring Radiation Sources 3.1 mSv (~50%) is from naturally occurring sources Radon/Thoron – 2.3 mSv per year Internal radiation – 0.28 mSv per year Terrestrial radioactivity – 0.19 mSv per year Cosmic radiation – 0.34 mSv per year
11	Sources of Ionizing Radiation: Naturally Occurring Radiation Sources Radium (Ra-226) is a decay product of U-238 found in the soil and has a half-life (T_½) of 1620 years Radon is an alpha emitter with a T_½ of approx. 4 days Thoron gas – is also a radioactive isotope of radon T_½= 55 seconds
12	Sources of Ionizing Radiation: Naturally Occurring Radiation Sources Exposures increase with altitude approx. doubling every 1500 m as there is less atmosphere to attenuate the cosmic radiation Leadville, Colorado (3200 m): 1.25 mSv/year More at poles than equator Airline crews and frequent fliers receive an additional ~ 1 mSv/yr 5 hour transcontinental flight will result in an equivalent dose of ~ 25 mSv Apollo astronauts – 2.75 mSv during the lunar missions
13	Sources of Ionizing Radiation: Naturally Occurring Radiation Sources Ingestion of food and water containing primordial radionuclides K-40 is most significant T_½ = 1.3x10⁹ yrs 1.33 MeV e^-/1.46 MeV ^g 0.01% abundance Skeletal muscle has the highest concentration of potassium in the body
14	Sources of Ionizing Radiation: Naturally Occurring Radiation Sources High Z decay chains U-238 – isotope of uranium Th-232 – thorium – at least 3-4x more abundant than uranium in the earth’s crust K-40 – potassium – naturally occurring radionuclide; typically ~0.1 μCi in the body (about 200,000 decays per minute) Varies by location
15	Sources of Ionizing Radiation: Technology-Based Radiation Sources Medical radiation totals about 3.0 mSv per year Approximately 50% of all annual exposures… compared to the previously reported one-third in NCRP report #93
16	Sources of Ionizing Radiation: Technology-Based Radiation Sources Medical radiation totals about 3.0 mSv per year Computed Tomography increased nearly 10-11% annually in the past two decades NCRP 100 (pub. 1989): 3,700 person Sv Current Estimations: ~440,000 person Sv (Eff Dose per capita ~1.5 mSv)
17	Sources of Ionizing Radiation: Technology-Based Radiation Sources
18	Sources of Ionizing Radiation: Technology-Based Radiation Sources
19	Sources of Ionizing Radiation: Technology-Based Radiation Sources
20	Sources of Ionizing Radiation: Technology-Based Radiation Sources
21	Sources of Ionizing Radiation: Technology-Based Radiation Sources Medical radiation totals about 3.0 mSv per year
22	Regulatory Agencies and Advisory Bodies Radiation Dose Limits U.S. Nuclear Regulatory Commission ALARA
23	Regulatory Agencies U.S. Nuclear Regulatory Commission (NRC) regulates special nuclear material, source material, by-product material of nuclear fission, regulates the maximum permissible dose equivalent limits Agreement states arrange with the NRC to self-regulate medically related licensing and inspection requirements of radioactive materials 10 CFR Parts 20 (standards for protection against radiation) 10 CFR Parts 19, 30, 32, 35, 110 Food and Drug Administration (FDA) regulates radiopharmaceutical development, manufacturing, performance and radiation safety requirements associated with the production of commercial x-ray equipment U.S. Department of Transportation (DOT) regulates the transportation of radioactive materials State Regulations – WAC = Washington Administrative Code WAC246-225 – Radiation Protection (x-rays in the healing arts)
24	Advisory Bodies NCRP – National Council on Radiation Protection and Measurements Collect, analyze, develop and disseminate, in the public interest, information and recommendations about radiation protection, radiation measurements, quantities and units ICRP – International Commission on Radiological Protection Similar to NCRP, however its international membership brings to bear a variety of perspectives on radiation health issues The NCRP and ICRP have published over 200 monographs containing recommendations on a wide variety of radiation health issues that serve as the reference documents from which many regulations are crafted IAEA – International Atomic Energy Agency JCAHO – Joint Commission on Accreditation of Healthcare Organizations ACR – American College of Radiology
25	Radiation Dose Limits
26	Occupational Exposures 1 mSv per year for diagnostic radiology is lower than expected because it includes personnel who receive very small occupational exposures 15 mSv per year or more are typical of special procedures utilizing fluoroscopy and cineangiography Again, occupational exposure limit is 50 mSv per year
27	Persons at Risk To determine appropriate dose limits and/or appropriate imaging protocols, distinguish between: Radiation workers Pregnancy identified Pregnancy status-unknown Staff not designated as radiation workers (i.e. schedulers, reception workers, volunteers, etc) Members of the public Fetus Patients Adult Pregnancy identified Pregnancy status-unknown Child
28	As Low As Reasonably Achievable ALARA Dose limits to workers and the public are regarded as upper limits rather than as acceptable doses or thresholds of safety In addition to the dose limits, all licenses are required to employ good health physics practices and implement radiation safety programs to ensure that radiation exposures are kept as low as reasonably achievable (ALARA), taking societal and economic factors into consideration The ALARA doctrine is the driving force for many of the policies, procedures, and practices in radiation laboratories, and represents a commitment by both employee and employer to minimize radiation exposure to staff, the public, and the environment to the greatest extent possible
29	Radiation Detection Equipment Personnel Dosimetry Radiation Safety Radiation Safety Officer (RSO)
30	Radiation Detection Equipment: Ionization Chambers and Survey Meters Characteristics of equipment are optimized for specific applications Sensitivity Energy resolution Calibrated annually (required by state/federal agencies) – NIST traceable Ionization chambers – physics testing
31	Radiation Detection Equipment: Ionization Chambers and Survey Meters Survey meters – radioactive contamination, ‘source search’ US NRC definition: Any portable radiation detection instrument especially adapted for inspecting an area or individual to establish the existence and amount of radioactive material present.
32	Personnel Dosimetry: General Information Required for personnel expected to get more than 10% of the occupational dose. The dosimetry report lists the “shallow” equivalent dose, corresponding to the skin dose, and the “deep” equivalent dose, corresponding to penetrating radiation Generally placed at waist level or shirt-pocket level For fluoroscopy, placed at collar level outside the lead apron to measure radiation dose to thyroid and lens of eye Pregnant radiation workers typically wear a second badge at waist level (behind the lead apron, if used) to assess the fetal dose
33	Personnel Dosimetry: General Information
34	Personnel Dosimetry: Film Badge A pack containing film is placed inside a special plastic film holder Using metal filters (typically lead, copper, and aluminum) the relative optical densities of the film underneath the filters can be used to identify the general energy range of the radiation and allow for the conversion of the film dose to tissue dose Open window (J) where film is not covered by a filter or plastic and is used to detect medium and high-energy beta radiation
35	Personnel Dosimetry: Thermoluminescent Dosimeters (TLD) TLD is a dosimeter in which consists of a scintillator in which electrons become trapped in excited states after interactions with ionizing radiation If the scintillator is later heated, the electrons can then fall to their ground state with the emission of light Thermoluminescent means emitting light when heated The amount of light emitted by the TLD is proportional to the amount of energy absorbed by the TLD After TLD has been read, it may be baked in an oven and reused
36	Personnel Dosimetry: Thermoluminescent Dosimeters (TLD) Lithium Fluoride (LiF) is one of the most useful TLD materials LiF TLDs have a wide dose response range of 10 mSv to 10³ mSv Used in nuclear medicine to record extremity exposures Landauer ring Lithium fluoride (LiF) crystal structure Measures x-ray, gamma-rays, and beta radiation
37	"OSL is similar to TLDs..." OSL is similar to TLDs except that the light emission is stimulated by a laser light instead of heat Crystalline aluminum oxide activated with carbon (Al₂O₃:C) is commonly used Broad dose response range like TLDs They can be reread several times Landauer Luxel ® Badge Measures x-ray, gamma-rays, and beta radiation with optional neutron detection (CR-39 incorporated into plastic film pack)
38	Personnel Dosimetry: Summary
39	Radiation Protection & Exposure Control Time Distance Shielding
40	Radiation Protection & Exposure Control Time Reduce the time spent near a radiation source Direct relationship between time and exposure Exposure rates – constant radiation sources (radionuclides) vs. “on/off” radiation Diagnostic x-ray equipment usually produces high exposure rates in brief intervals Radionuclides – generally low exposure rates over extended periods Use time efficiently and wisely Understand task to perform Utilized appropriate equipment Example: Injection of FDG (F-18; 511 keV) – practice with non-radioactive source first, injections should be done in lead shielded syringe
41	Radiation Protection & Exposure Control Distance – Inverse Square Relationship
42	Radiation Protection & Exposure Control Distance – Inverse Square Relationship Rule of thumb (diagnostic energy range): At 1 m from a patient at 90 degrees to the incident beam, the radiation intensity is 1/1000^th the intensity of the beam incident at the patient More precisely: 0.1% - 0.15% (0.001 to 0.0015) of the intensity of the beam incident upon the patient for a 400 cm² area field area The NCRP recommends that personnel should stand at least 2 m from the x-ray tube and the patient and behind a shielded barrier or out of the room, whenever possible
43	Radiation Protection & Exposure Control Shielding Shielding is used to reduce exposure to patients, staff and the public Radiation suite walls and windows Moveable shields – important in fluoroscopy suites Scatter plots – utilize room layout (i.e. CT angio) Shielding calculations determine the thickness of an attenuating material required to reduce radiation exposure to acceptable levels
44	Radiation Protection & Exposure Control Shielding – Room Designs Typical shielding Mammo: gypsum wallboard (usually 2 sheets, 1.6 cm thick) Gen Rad/Fluoro: lead (1/32” to 1/16”) Fluoro – II absorbs primary beam CT: Walls – lead (1/16” to 1/8”) Ceiling/floors – concrete (standard thickness with some lead, or thicker concrete slab) Shielding against Primary (focal spot) Scattered (patient) Leakage (x-ray tube housing, <100 mR/hr @ 1 m from housing)
45	"NCRP Report #147 –..." NCRP Report #147 – Structural Shielding Design for Medical X-ray Imaging Facilities Estimated workload (W) – depends on techniques and patient load Estimate of total x-rays produced per week Fluoroscopy – W = (mA • min/week) General Radiography – W = (mGy/week); this is based on average # patients per week and average mGy per patient Estimated total of x-rays incident on any given wall depends on whether it is a primary or secondary barrier Distance (d) – measured from source of radiation to the area to be protected (inverse square principle) Room sizes affect amount of additional shielding in walls
46	Radiation Protection & Exposure Control Shielding – Room Designs (Primary or Secondary)
47	"Use factor (U) –..." Use factor (U) – indicates the fraction of time during which the radiation under consideration is directed at a particular barrier U ranges between 0 and 1 for primary barriers Accounts for rooms with wall/table bucky verses wall only or table only rooms U = 1 for secondary barriers (ALWAYS)
48	Radiation Protection & Exposure Control Shielding – Room Designs
49	Radiation Protection & Exposure Control Shielding – Room Designs Occupancy factor, T, indicates the fraction of time during a week that a single individual might spend in an adjacent area T = 1 for full occupancy (work areas, offices etc.) T = 1/2 for exam rooms and treatment areas T = 1/5 for partial occupancy (corridors, staff rest rooms and lounges, etc.) T = 1/8 for doors T = 1/20 for occasional occupancy (waiting rooms, public rest rooms, storage rooms etc.) T = 1/40 for rare occupancy (outdoor areas w/transient pedestrian/vehicle traffic, unattended parking garages, etc)
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51	"Lead usually used for shielding..." Lead usually used for shielding and specified as weight per square foot (lb/ft²) Typically 2 lb/ft² (1/32^th inch) or 4 lb/ft² (1/16^th inch) is sufficient for diagnostic radiology Calculated using HVL and tenth value layer (TVL) of the material (1/2)ⁿ– reduction in beam intensity, n is HVL Shielding material used from base of floor to a height of 7 feet** Gen. rad. – same thickness of lead for entire wall (or even more simple, one thickness for all walls) CT – more complex designs (concrete slab directly beneath scanner, different lead thickness on each wall depending on distance from gantry isocenter to walls) Acrylic, leaded glass, gypsum drywall, steel are other materials used besides lead for shielding
52	Radiation Protection & Exposure Control Protection of Patient in Medical X-ray Imaging Miscellaneous Considerations Careful identification of patients (ID bracelets/Q-A) Determination of pregnancy status (very important!) Eliminate screening exams that only rarely detect pathology “Yearly” dental exams may not be appropriate for all patients Use of high speed dental film reduces dose “Yearly” screening mammography exams not appropriate for women younger than 40 years old (perhaps 50 years old) Technique errors and high repeat rates can be avoided by posting technique charts and using phototiming Good quality control program to eliminate equipment and processor problems
53	"Fluoroscopy" Fluoroscopy Use high dose techniques judiciously – maximum 10 R/min in standard mode vs. 20 R/min in ‘boost’ mode (WAC246-225-050(3)); also new technology of ‘3-D spin’
54	Example Board Question The annual recommended dose to the lens of the eye of a radiation worker is: A. 500 mSv B. 150 mSv C. 50 mSv D. 5 mSv E. 1 mSv
55	Example Board Question The recommended weekly effective dose equivalent permitted for radiologists under current regulations is: A. 10 mSv B. 50 mSv C. 100 mSv D. 0.5 mSv E. 1.0 mSv
56	Example Board Question Regulations limit the dose equivalent to the embryo/fetus of a declared pregnant radiation worker to ______ mSv/month. A. 50 B. 10 C. 5 D. 0.5 E. 0.1
57	Example Board Question According to NCRP Report No. 116, the recommended maximum annual dose equivalent for radiation workers' whole body is _____ mSv and for the hands is _____ mSv. A. 5 5 B. 5 50 C. 10 100 D. 50 50 E. 50 500
58	Example Board Question Film badges: A. Can measure only the total dose of radiation, but cannot distinguish between low and high energy x-rays. B. Can measure dose of 0.01 mSv. C. Are insensitive to heat. D. Use the optical density of the film to measure dose.
59	"A shielding design for a..." A shielding design for a diagnostic or therapy installation, when there is no restriction on the beam direction, must: A. Consider all walls as primary barriers. B. Assign all walls a use factor (U) of 1. C. Assign all areas adjacent to the installation an occupancy factor (T) of 1. D. Shield all areas to a radiation level of 1.0 mSv per week. E. Shield such that adjacent areas will not receive instantaneous exposure rates greater than 2 mR/hr.
60	"The occupancy factor (T)..." The occupancy factor (T) is changed from 1/16 to 1/2 and the activity factor (A) is doubled for a radiation source whose HVL is 0.3 mm Pb. In order to maintain the same level of protection, _____ mm Pb must be added to the shielding. A. 0.3 B. 0.6 C. 0.9 D. 1.2 E. 1.5