Follow-up studies on A-bomb survivors: implications for radiological protection

A-bomb survivor data are the principal basis for risk estimates for late somatic and genetic effects of radiation on man. The data concern radiation delivered at high dose rate and the risk estimates are dominated by persons with doses (kerma) of more than 100 rads. The estimates, therefore, may not be applicable to low doses received at low dose rates, where some advocate use of a dose-rate reduction factor of at least two for carcinogenesis. In contrast with dose-rate factors, little attention has been given to individual factors such as age. Even after more than 35 years, the experience of only the oldest A-bomb survivors (aged over 50 in 1945) is essentially complete. It appears, however, that the risk of carcinogenesis may depend upon age at exposure and that relative risk may be a more appropriate measure than absolute risk. Limits for occupational or population exposures were not developed on the basis of risk estimates; such estimates can, however, be used to calculate the possible consequences of exposure standards. In contrast to carcinogenesis, which has been shown clearly in the data on A-bomb survivors, and despite the appearance of chromosome aberrations, no evidence of radiation-induced mutations in the children of survivors has yet been detected