CT scans in childhood and risk of leukaemia and brain tumours

Abstract

1that excess risk of leukaemia is associated with the doses of ionisation radiation to red bone marrow from CT scans, which provides solid justifi cation for the “image gently” campaign. However, we disagree with their statement that the dose response of leukaemia does not vary with the age at exposure. According to Cristy, 2 the amount and distribution of red bone marrow changes dramatically with age in childhood, and gradually concentrates in some body parts at adulthood. We have shown 3 that variation in physical bone density in people of the same age, and uneven body development with age, can greatly aff ect the accuracy of the age-dependent estimation of radiation doses to red bone marrow. Therefore, one should be careful in applying the reported excess relative risk per unit dose to estimate the leukaemia risk in a large population. In Pearce and colleagues’ study, the red-bone-marrow dose from a CT scan is a single number for a specifi c age and sex. This is clearly an oversimplifi cation which could have caused the reported irrelevance of the dose response of leukaemia to such personal characteristics as age at exposure or time since exposure. The lack of association is in stark contrast to many previous studies that have reported a sharp decrease in risk with age at exposure. 4