NEW ICRP LUNG DOSIMETRY AND ITS RISK IMPLICATIONS FOR ALPHA-EMITTERS

This paper follows on from Dr Bair's description of the new ICRP lung model, by illustrating its practical application to the calculation of dose coefficients for different forms of long-lived, alpha-emitting a erosols of plutonium and uranium. At the other end of the dosimetric s pectrum, the dosimetry of the short-lived, alpha-emitting progeny of r adon are examined. The conclusion is that, when applied to radon proge ny exposures, the new ICRP lung dosimetry provides an opportunity to e xamine more critically the risk factors that are currently assumed for alpha radiation doses received by lung tissues. The results of large scale studies of lung cancer in uranium miners indicate that one Worki ng Level Month (WLM) of exposure to radon progeny is equivalent in ter ms of lifetime lung cancer risk to approximately 5 mSv of effective do se. The currently recommended risk factors include the radiation weigh ting factor (W-R(alpha)), the total detriment per sievert at high dose rate (DE(H)), the dose and dose rare effectiveness factor (DDREF), an d the lung-tissue weighting factor (W-T(lung)). However, consideration of the uncertainties involved in calculating the effective dose per u nit exposure using the new lung model with the currently recommended r isk factors shows that it is very unlikely to be as low as 5 mSv per W LM. The most likely estimate is threefold higher, about 15 mSv per WLM . Can this argument be used to provide a more realistic value of a com posite risk weighting factor for all alpha emitters in the lungs? If s o, the appropriate lung cancer risk factor, say Omega = (WRWTlung)-W-a lpha(DE(H))(DDREF) would be about 0.05 per Gy. The value published by Dr Bair in 1976 from his classic study in dogs was 0.06 per Gy!