A-bomb survivors: factors that may lead to a re-assessment of the radiation hazard.

BACKGROUND The study cohort of the survivors of the A-bombs in Japan, used as the basis of the internationally accepted estimates of cancer radiation risk, was collected more than 5 years after the bombing and did not include those who died of bomb-related injuries before that date. This paper tests whether the people who survived, in spite of bomb-related injuries, are homogeneous in respect of variation of cancer risk with age with survivors without such injuries. METHODS Appropriate statistical models are derived and fitted to survivor data by maximum likelihood and the resultant statistics used to test the homogeneity assumption. RESULTS Significant differences were found between those with no injuries and those with multiple injuries and shown to be largely due to exposures before 10 or after 55 years of age having exceptionally high risks of late effects of radiation for survivors showing early effects, i.e. bomb-related injuries. CONCLUSIONS Certain accepted dogmas about the biology of radiation risks in humans, such as 'cancer is the only late effect of radiation' and 'leukaemia is uniquely radiogenic amongst cancers', may be significantly in error. These are discussed.