We previously published a Heads Up of a UK study showing that computerised tomography (CT) brain scans were associated with an approximately threefold, dose-related, increased risk of brain tumour or leukaemia. Now, an Australian data linkage study used Medicare records to identify which of the 10.9 million persons aged 0–19 years had any CT scans over a mean period of 9.5 years and national cancer records to identify which of them developed cancers. Patients were excluded if their CT scan was taken within one year of a cancer diagnosis, in case the scan was part of the cancer diagnostic procedure. The cancer incidence in the 6.2% of the population who had any scan was 24% greater than for those with no scan, and there was a dose response: the risk increased with increasing numbers of scans (Fig. 1). All sites of CT scan were associated with increased risk of cancer, but the increased risk was greater for brain (73%), chest (62%) and abdomen or pelvis (61%), and lower for facial bones (14%) and spine or neck scans (13%). The cancer risk was greater the younger the age at which the CT scan was performed, being 35% greater in children aged 1–4 years. The risk was increased to about the same extent (20–25%) for many solid cancers, lymphoid cancers and leukaemia. The absolute excess risk for all cancers was 9.38 per 100 000 years at risk. Doctors should think twice before ordering CT scans.
Reviewers: David Isaacs, firstname.lastname@example.org; Alyson Kakakios, Children's Hospital at Westmead, Westmead, NSW, 2145