The risk of cancer from computerised tomographic (CT) scans was deduced from radiation exposure to the atomic bomb in Japan and open to methodological criticism. Now a retrospective UK cohort study has used a national cancer registry to examine the association between CT brain scan and brain tumour or leukaemia in children and young adults <22 years old who had CT scans prior to developing malignancy. The 24-year study found a positive association between CT scans and both leukaemia and brain tumours, and the risk increased with increasing dose (Figure). The relative risk of leukaemia or brain tumour approximately tripled for patients who received a moderate cumulative radiation dose compared with patients who received a low dose. These cancers are uncommon and the cumulative absolute risk is small: an estimated one excess case of leukaemia and one excess case of brain tumour per 10 000 head CT scans in the 10 years after the first scan for patients <10 years old. The benefits of each and every CT brain scan should be carefully assessed. Radiation doses from CT scans should be kept as low as possible and the possibility should be considered of an alternative such as magnetic resonance imaging or even forgoing a scan.
Reviewer: David Isaacs, firstname.lastname@example.org