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Use of Effective Dose as an RDRC Study Limit

Use of Effective Dose as an RDRC Study Limit. Wayne L Thompson University of Tennessee Medical Center. RDRC Study Dose Limits. Since 1975, 21 CFR 361.1(b)(3)(I) has specified

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Use of Effective Dose as an RDRC Study Limit

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  1. Use of Effective Dose as an RDRC Study Limit Wayne L Thompson University of Tennessee Medical Center

  2. RDRC Study Dose Limits Since 1975, 21 CFR 361.1(b)(3)(I) has specified • 3 rem single exam, 5 rem annual and total commitment limit, to whole body, blood forming organs, eye lens, and gonads from all sources. • 5 rem single exam, 15 rem annual and total commitment limit, to other organs from all sources.

  3. Evolution of “Body Dose” • #1: Whole Body Dose / Total Body Dose (historically different origins but used interchangeably for radiopharmaceuticals in literature) • #2: Effective Dose Equivalent • #3: Effective Dose

  4. #1: Whole/Total Body Dose • Used by ICRP (Int Comm on Rad Prot)in 1959, and by Society of Nuc Med for MIRD dose in 1968. • Assumed entire radioactive decay energy is uniformly distributed throughout all body organs and compartments = oversimplification. (Almost never true, except for 3H and maybe 137Cs). • Ignores differences in organ and tissue sensitivities • But, there was nothing better at the time.

  5. #2: Effective Dose Equivalent • ICRP 26 (1977): adopted this new concept for occupational absorbed dose. • Employs sensitivity weighting factors for six tissues. Ex: sensitive gonads = 0.25, less sensitive bone surfaces = 0.03. • Sum of (organ doses • tissue sensitivity weighting factors) produces single value to measure stochastic risk to radiation worker from non-uniform irradiation. • NRC (1994) adopted as occupational dose limit in 10CFR20

  6. #3: Effective Dose • ICRP 60 (1991) increased # sensitive organs from six to twelve and updated tissue weighting factors, formerly based on radiation workers (ex: inhalation, ingestion, mostly males, etc), to new ones based on general population (ex: equal number males and females, etc). • Effective dose widely recognized as most accurate measure of total potential detriment (fatal and non-fatal cancer induction, serious hereditary defects, and life shortening) from stochastic effects of radiation exposure.

  7. #3: Effective Dose • ICRP 80 (1999): “The effective dose can also be used to provide a relative index of harm for various procedures in diagnostic radiology and nuclear medicine”. • ICRP periodically publishes tables with effective dose for new radiopharmaceuticals • OLINDA (successor to MIRDOSE) software gives researchers practical means to perform MIRD technique effective dose calculations for new radiopharmaceuticals using vast database of ~ 850 radionuclides.

  8. #3: Effective Dose • ICRP tables list effective dose separately for: • Adults • 1, 5, 10, and 15 year old children • Males and females • Allows some risk matching to subject body, though still uses the standard age and sex averaged tissue weighting sensitivity factors.

  9. #3: Effective Dose • Brief poll shows many institution’s now use effective dose (sometimes as loose interpretation of whole body dose) as a guideline for research subject dose limit. • NIH uses effective dose as guideline in their brochure “An Introduction to Radiation for NIH Research Subjects” and requires its calculation for all research studies.

  10. Three Choices • #1: Stick with Whole body dose - outdated Oversimplification  Can underestimate stochastic risk by factor of up to 100 compared to effective dose. • #2: Effective Dose Equivalent -step in right direction Required for NRC occupational dose. • #3: Effective Dose - best Most accurate for true risk estimate. Easily combines x-ray and radiopharmaceutical dose per RDRC.

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