Child CT scans ‘can triple risk of cancer’

Scientists have called for greater efforts to ensure use of the scans are justified although they stress the risks remain very small.

British-led scientists studied information on around 180,000 patients under the age of 22 who had CT scans at UK hospitals between 1985 and 2002. Their cancer rates were compared with those from the general population.

The results showed that children younger than 15 would receive enough radiation from two to three head CT scans to triple their risk of developing brain cancer.

Because brain and bone marrow do not absorb X-rays at the same rate, the figures for leukaemia are slightly different. In this case, five to 10 head scans was sufficient to triple the cancer risk.

The findings are published in the latest online edition of The Lancet medical journal. They showed that the chances of an individual developing cancer after a CT scan remain tiny. For children under 10 receiving head scans, around one extra case of leukaemia and one extra brain tumour per 10,000 patients would be expected during the decade after the procedure.

The study did not look at the reasons why the children underwent CT scans, but ensured it was not because they already had brain tumours or leukaemia.

CT scans are used to examine patients with a range of conditions including brain tumours, bone disorders, and injuries to internal organs.

Lead researcher Mark Pearce, of Newcastle University, said: “Further refinements to allow reduction in CT doses should be a priority, not only for the radiology community, but also for manufacturers.

“Alternative diagnostic procedures that do not involve ionising radiation exposure, such as ultrasound and MRI (magnetic resonance imaging), might be appropriate in some clinical settings.

“Of utmost importance is that where CT is used, it is only used where fully justified from a clinical perspective.”

Commenting in The Lancet, Andrew Einstein, from Columbia University Medical Centre in New York, said: “Use of CT scans continues to rise, generally with good clinical reasons, so we must redouble our efforts to justify and optimise every CT scan.”

Prof Richard Wakeford, from the Dalton Nuclear Institute at Manchester University, said: “The measures taken to protect against radiation exposure assume that any dose of radiation, including from exposures for medical purposes, carries with it some risk, but that the risk from low doses (such as received during CT scans) is small.

“The radiation risks the study has detected are at the level currently assumed for the purposes of radiation protection, ie small, which is reassuring.

Prof Wakeford added: “However, as with all sources of radiation exposure, this small risk should be taken into account when radiation is used.”

Prof David Spiegelhalter, Winton Professor of the Public Understanding Of Risk at Cambridge University, said: “This study suggests there is around a one in 10,000 chance that a young person’s CT scan will give them leukaemia over the next 10 years.

“This is important, but the CT scan may be even more important – a judgment has to be made.”