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

Since 1975, 21 CFR 361.1(b)(3)(I) has specified 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.

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

#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.

#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

#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.

#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.

#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.

#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.

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.