Eric J. Hall, D.Phil., D.Sc., F.A.C.R., F.R.C.R.

1. Dose Limits for Studies Under an RDRC Eric J. Hall, D.Phil., D.Sc., F.A.C.R., F.R.C.R. Higgins Prof. of Radiation BiophysicsChair RDRC, Columbia University, N.Y.Consultant to the FDA

2. Rationale • The present limits date from the 1970s. • Since then, BEIR and UNSCEAR have revised their cancer risk estimates. • ICRP introduced “Effective Dose” and Tissue Weighting Factors (WT). • NCRP (116) reduced dose limits.

3. Rationale • Limits for research subjects based on occupational exposure limits. • NCRP now recommends a cumulative limit of 0.01 Sv (I rem) per annum. • ICRP now recommends an annual limit of 0.02 (2 rem).

4. Current Limits (1975) Whole body, blood forming organs, lens of the eye, and gonads: • Single dose………………………………...3 rem • Annual and total dose commitment…...5 rem Other organs: • Single dose…………………………………5 rem • Annual and total dose commitment….15 rem

5. Discussion • No justification to single out: a) Ocular lens; radiation risk is deterministic with large threshold. b) Blood forming organs; leukemia as principle risk reflects thinking of the 1970s.

6. Discussion • To the accuracy that we know WT values, we can ascribe a value of 0.1 to all organs. • In the current ICRP scheme, WT for radiogenic organs is 0.05 or 0.12. The current value for the gonads (0.20) is being revised downwards.

7. ICRP Tissue Weighting Factors WT

8. Proposed Revised Limits

9. Attributable Lifetime Risk

10. Pediatric Subjects • The variation of sensitivity to radiation induced cancer is so great that three age ranges are justified: 05 years 618 years >18 years