CT scans increase risk of cancer in children and adolescents

Two to three computed tomography (CT) scans of the head may triple children’s risk of brain cancer; five to ten such scans may triple the risk of leukaemia.

This was seen in a study of all people under 22 years of age who had a first CT scan within the NHS in England, Wales, or Scotland between 1985 and 2002. Linkage with the central NHS registry provided data for the incidence of cancer in these people over an average of 10 years, and up to 23 years, of follow-up.

During this time, 74 diagnoses of leukaemia and 135 diagnoses of brain cancer were recorded in more than 175 000 participants. Excess relative risk per mGy was 0.036 (95% CI 0.005 - 0.120) and 0.023 (0.010 - 0.049) for leukaemia and brain tumours, respectively. For every 10 000 head CT scans performed in children under 10 years, one additional case of leukaemia and one additional brain tumour can be expected in the subsequent 10 years.

Up to a half of CT scans are done unnecessarily, writes the commentator. Because we now know that CT confers an increased, albeit small, risk of cancer, good clinical judgement is needed to justify performing each CT scan, using as low a dose as possible.

Pearce MS, et al. Lancet, Early Online Publication, 7 June 2012. doi:10.1016/S0140-6736(12)60815-6.