Cases and matched controls came from the National Registry of Childhood Tumours. Cases were cancers registered for children born and diagnosed in Great Britain during 1980 to 2006.
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 a predictive map for radon. 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 childhood cancers were not significant for any radiation type. Excess risk was insensitive to alternative adjustments for socio-economic status.
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 magnitude and specificity of the results. The association is therefore likely to be causal.
Our results suggest that risks of childhood leukaemia apply at natural background levels of exposure at about the level extrapolated from high dose-rate data.