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

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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

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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.

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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).

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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 dose5 rem
• Annual and total dose commitment.15 rem

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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.

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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.

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ICRP Tissue Weighting Factors WT
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Proposed Revised Limits
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Attributable Lifetime Risk
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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
• gt18 years

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