Risk of CNS cancers among survivors of the Hiroshima and Nagasaki atomic bomb blasts

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This cohort study investigated the risk of central nervous system (CNS) cancers among the atomic bomb survivors of Hiroshima and Nagasaki based on their estimated radiation exposure. Between 1958 and 2009, there was 285 cases of CNS cancers out of a cohort of 105,444 atomic bomb survivors with radiation dose estimates. The study examined the risk of these cancers as excess relative risk (ERR) per gray (Gy) (ERR/Gy). The authors reported ERR/Gy for glioma as 1.67 (95% confidence interval (CI) 0.12 to 5.26), for meningioma 1.82 (95% CI: 0.51 to 4.30), for schwannoma 1.45 (95% CI − 0.01 to 4.97), and for all CNS tumours combined 1.40 (95% CI: 0.61 to 2.57). Further, the authors reported a trend of increasing rates of CNS tumours with increased radiation exposure, with an apparent linear dose response. The authors concluded that the radiation exposure from the atomic bombs is associated with elevated risks of CNS tumours in general, and was significant for glioma and meningioma. There was a higher but non-significant association with schwannoma. 

Radiation risk of central nervous system tumors in the Life Span Study of atomic bomb survivors, 1958–2009

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The study reported a significant association with CNS tumours. However, the results also highlight the difficulty of examining the risk of radiation exposure at low levels, especially when examining the occurrence of rare diseases such as CNS tumours. Interestingly, in this study the unexposed control group was reported to have a higher rate of CNS cancers overall than that of the exposed groups with assigned dose of less than 1 Gy. The study attempts to show that at low radiation doses there is still a linear dose response; however, the limitations and inconsistencies in this study prevent this conclusion. Overall, the results of this study are unclear at low levels. This is consistent with the position held by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) that states at low levels (less than 100 milligray) the possible increased risk of cancer from radiation exposure is uncertain (UNSCEAR, 2017).