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Mark Little, D.Phil., were able to quantify—for the first time—excess risk for leukemia and other myeloid malignancies following low-dose exposure to ionizing radiation in childhood. More than two-fold increased risk and higher was observed for cumulative exposures less than 100 milliSieverts (mSv); excess risk was also apparent for cumulative doses of less than 50 mSv for some endpoints. The findings were published online July 16, 2018 in Lancet Haematology.

Because these diseases are rare, the excess absolute risk in the population is estimated to be small. Nevertheless, given the ubiquity of exposure, primarily from medical procedures like computed tomography

CT) scans, every effort should be made to minimize doses, especially for children.

Although substantial evidence links exposure to moderate or high doses of ionizing radiation, particularly in childhood, to increased risk of leukemia, prior to this study the association of leukemia with exposure to low-dose radiation was not well-established. Evaluating risks at low-doses, under 100 mSv, is crucial since this is the range most relevant to the general population. Additionally, some have suggested that this level, about 100 mSv, may represent a threshold dose of radiation below which there is no excess risk of leukemia. Evidence from this study suggests, on the contrary, that there is significant risk even at these lower doses, and that the current system of radiological protection is prudent and not overly protective.

Data for this analysis came from more than 250,000 individuals aged 21 or younger at the time of first exposure and were contributed from nine cohort studies (from Canada, France, Japan, Sweden, the UK, and the US) enrolled between June 4, 1915, and December 31, 2004.

Reference: Little, M. et al. Leukaemia and myeloid malignancy among people exposed to low doses (<100 mSv) of ionizing radiation during childhood: A pooled analysis of nine historical cohort studies. Lancet Haematology. DOI: 10.1016/S2352-3026(18)30092-9