Results of a record-based case-control study of natural background radiation and the incidence of childhood cancers in Great Britain

摘要

Background Although there is abundant evidence that moderate and high doses of radiation can cause leukaemia and other cancers, there is little direct evidence on the leukaemogenic (or other carcinogenic) effects of ionizing radiation at low doses and dose rates, in particular in children, suspected of being at highest risk. Aims To test the association between childhood cancers and natural background radiation. Methods Childhood cancer cases born and diagnosed in Great Britain during 1980-2006 and1-2 matched controls per case were taken from the National Registry of Childhood Tumours. Radiation exposures were estimated for mother's residence at the child's birth from national databases, using the County-District mean for gamma-rays, and from a predictive map based on domestic measurements grouped by geological boundaries for radon. Results Among 27 447 cancer cases and 36 793 controls there was 12% excess relative risk (95% CI 3, 22; 2-sided p=0.01) of childhood leukaemia per millisievert of red-bone-marrow dose from gamma radiation; the association with radon was not significant. Associations for other sites of childhood cancer were not significant for any radiation type. Excess risk was insensitive to adjustment for measures of socio-economic status, and is consistent with high dose-rate risks in the Japanese atomic-bomb survivors. Conclusions The statistically significant leukaemia risk reported in this reasonably-powered study (power ～50%) is consistent with high dose-rate predictions. Substantial bias is unlikely, and we cannot identify mechanisms by which confounding might plausibly account for the observed magnitude and specificity of the association between environmental gamma radiation and childhood leukaemia. The association is therefore likely to be causal. Our results suggest that childhood leukaemia risks extrapolated from high dose-rate data apply at natural background levels of exposure.