Multiple CT scans in childhood can triple the risk of developing brain cancer or leukaemia, a study suggests.
The Newcastle University-led team examined the NHS medical records of almost 180,000 young patients.
But writing in The Lancet the authors emphasised that the benefits of the scans usually outweighed the risks.
They said the study underlined the fact the scans should only be used when necessary and that ways of cutting their radiation should be pursued.
During a CT (computerised tomography) scan, an X-ray tube rotates around the patient’s body to produce detailed images of internal organs and other parts of the body.
In the first long-term study of its kind, the researchers looked at the records of patients aged under 21 who had CT scans at a range of British hospitals between 1985 and 2002.
Because radiation-related cancer takes time to develop, they examined data on cancer cases and mortality up until 2009.
Brain cancer and leukaemia are rare diseases.