Impact on radiation risk estimates of possible selection effects in Japanese A-bomb survivors: Reanalysis of data on acute radiation symptoms

Estimates of radiation-induced cancer risks are based largely on the Life Span Study (LSS) of Japanese A-bomb survivors. Stewart and Kneale (2000) examined the possibility of bias in the LSS cohort by studying survivors with bomb-related acute injuries and those without such injuries. They reported significantly higher radiation risks for cancers and non-cancers among those survivors with acute multiple injuries compared with those without. The risks were particularly large among survivors aged <10 or ≥ 55 years of age at the time of bombing. This paper examines Stewart and Kneale’s findings more closely using the same LSS data on acute effects. All of the analyses have been carried out with Poisson regression methods. Models describing the trend in relative risk with dose have been fitted with adjustment for sex and time. Statistically significant differences in relative risk between survivors with epilation injury and those without have been found for leukaemia. There is also some evidence for heterogeneity in the leukaemia risk between those with two or more (multiple) injuries, those with no injuries and the remaining group of survivors (residue), but the evidence is weaker when survivors with one or more injuries are compared with those without injuries. For solid cancers, cardiovascular disease and all deaths, the relative risks do not differ significantly between survivors with multiple injuries, without injuries and the residual group. There is no significant evidence of heterogeneity in the relative risk between age-at-exposure categories for survivors with injuries. The relative risk estimates and their uncertainties are comparatively large for survivors exposed at ages <10 years, but this is not the case for survivors exposed at 55 years of age or more. The findings from the present work are inconsistent with those of Stewart and Kneale. No strong differences in radiation risks have been found between survivors with acute injuries and those without injuries.