The risks of childhood leukaemia from low-level radiation exposure

Exposure to ionizing radiation is an established cause of leukemia in childhood (<15 years). Both irradiation of the fetus (using data on medical exposure from the large case-control study of the Oxford Survey of Childhood Cancers), and irradiation of the child (using data from Japanese A-bomb survivors) have been shown to produce an excess risk of childhood-leukemia. The latest assessment of these risks have yielded coefficients of around 2 x 10-5 excess childhood leukemia cases per mSv for fetal exposure, around 1.5 x 10-5 excess childhood leukemia cases per mSv for irradiation in early infancy, this latter risk coefficient reducing with advancing age at exposure . The closeness of the risk coefficients for exposure just before and after birth (derived from different sources of information) is reassuring. It is these coefficients that are used in assessing the risk of childhood leukemia due to, say, the operation of a nuclear facility, and such assessments have demonstrated that the risk due to normal operations will produce a very small number of extra cases, a 'signal' that will not be detectable above the unavoidable 'noise' of statistical fluctuations in background incidence rates . However, reports of childhood leukemia 'clusters' near certain nuclear installations in Britain have led to the accuracy of these assessments being challenged.