PROBABILITY DISTRIBUTION OF DOSE AND DOSE-RATE EFFECTIVENESS FACTORFOR USE IN ESTIMATING RISKS OF SOLID CANCERS FROM EXPOSURE TO LOW-LETRADIATION

摘要

This paper presents an analysis to develop a subjective state-of-knowledge probability distribution of a dose and dose-rate effectiveness factor (DDREF) for use in estimating risks of solid cancers from exposure to low-LET radiation (photons or electrons) whenever linear dose-responses from acute and chronic exposure are assumed. A DDREF represents an assumption that the risk of a solid cancer per Gy at low acute doses or low dose rates of low-LET radiation, RL, differs from the risk per Gy at higher acute doses, RH; RL is estimated as RH/DDREF, where RH is estimated from analyses of dose-responses in Japanese atomic-bomb survivors. A probability distribution to represent uncertainty in a DDREF for solid cancers was developed from analyses of epidemiologic data on risks of incidence or mortality from all solid cancers as a group or all cancers excluding leukemias, including (1) analyses of possible nonlinearities in dose-responses in atomic-bomb survivors, which give estimates of a low-dose effectiveness factor (LDEF), and (2) comparisons of risks in radiation workers or members of thepublic from chronic exposure to low-LET radiation at low dose rates with risksin atomic-bomb survivors, which give estimates of a dose-rate effectivenessfactor (DREF). Probability distributions of LDEFs and DREFs for solid cancerincidence and mortality were combined using assumptions about the relativeweight that should be assigned to each estimate to represent its relevance toestimation of a DDREF. The probability distribution of DDREF for solid cancersdeveloped in this study has a median (50^th percentile) and90% subjective confidence interval (CI) of 1.3 (0.47, 3.6). The harmonicmean is 1.1, which implies that the arithmetic mean of an uncertain estimate ofthe risk of a solid cancer per Gy at low acute doses or low dose rates oflow-LET radiation is only about 10% less than the mean risk per Gy athigher acute doses. We also evaluated data to define a low acute dose or lowdose rate of low-LET radiation, i.e., a dose or dose rate below which a DDREFshould be applied in estimating risks of solid cancers.