BACKGROUND: The risk of developing nervous system tumors following exposure to 
ionizing radiation is not well quantified. We characterized the incidence of 
nervous system tumors among atomic bomb survivors as a function of radiation 
dose.
METHODS: Tumors of the nervous system and pituitary gland diagnosed between 1958 
and 1995 among 80 160 atomic bomb survivors were ascertained using the Hiroshima 
and Nagasaki tumor registries, medical records, and death certificates. 
Pathologists reviewed slides and medical records to provide histologic 
diagnoses. Poisson regression analyses were used to characterize radiation 
effects on tumor incidence, which are expressed as excess relative risk per 
sievert (ERR(Sv)). All statistical tests were two-sided.
RESULTS: A statistically significant dose-related excess of nervous system 
tumors was observed in the cohort (ERR(Sv) = 1.2, 95% confidence interval [CI] = 
0.6 to 2.1). The highest ERR(Sv) was seen for schwannoma (4.5, 95% CI = 1.9 to 
9.2). The risk for all other nervous system tumors as a group is also 
statistically significantly elevated (ERR(Sv) = 0.6, 95% CI = 0.1 to 1.3). Risk 
increases, although not statistically significant, were seen for meningiomas 
(ERR(Sv) = 0.6, 95% CI = -0.01 to 1.8), gliomas (ERR(Sv) = 0.6, 95% CI = -0.2 to 
2.0), other nervous system tumors (ERR(Sv) = 0.5, 95% CI = <-0.2 to 2.2), and 
pituitary tumors (ERR(Sv) = 1.0, 95% CI = <-0.2 to 3.5). The dose-response 
relationships were linear. For nervous system tumors other than schwannoma, 
excess risks were higher for men than for women and for those exposed during 
childhood than for those exposed during adulthood.
CONCLUSIONS: A statistically significant dose response was observed for all 
nervous system tumors combined and for schwannoma considered separately, 
indicating that exposure to even moderate doses (i.e., <1 Sv) of radiation is 
associated with an elevated incidence of nervous system tumors.