Repeated childhood CT scans increase risk of cancer in adulthood

Repeated CT scans during childhood can increase the risk of developing brain tumours or leukaemia in later life, research from the UK, US and Canada suggests.

A new study published in the Lancet indicates that brain tumours in later life were three times as common among people who had two to three CT head scans in childhood, while the risk of leukaemia was three times greater in patients receiving five to 10 scans during childhood.

But the researchers who carried out the study emphasise that the overall absolute risk of people developing cancer after receiving CT scans remains small – amounting to two extra cases of cancer per 10,000 children who received CT scans.

And an expert from Cancer Research UK noted that the use of CT scans in the UK is regulated and so is generally lower than in the other countries in the study.

As a result of their findings, the researchers recommend that the radiation doses delivered during CT scans should be as low as possible to reduce the associated risks.

The scientists – from Newcastle University, Dalhousie University in Canada and the Institutes of Health in the USA – assessed nearly 180,000 young patients in the UK who were given CT scans between 1985 and 2002.

Of these patients, 74 subsequently developed leukaemia, and 135 were diagnosed with brain cancer. The relative risk of leukaemia went up for each 0.036 mGy (microGrays – a unit of radiation exposure) of radiation that was received by those undergoing CT scans. For brain tumours, the risk increased per 0.023 mGy.

The study’s authors point out that regulations introduced in the UK in 2000 meant that CT scans are usually only used in the UK when they are justified by clinical need.

Lead author of the study, Dr Mark Pearce, said: “The immediate benefits of CT outweigh the potential long-term risks in many settings and because of CT’s diagnostic accuracy and speed of scanning, notably removing the need for anaesthesia and sedation in young patients, it will, and should, remain in widespread practice for the foreseeable future.”

Elizabeth Woolf, head of Cancer Research UK’s information website, CancerHelp UK, added: “This study provides further evidence to back up UK regulations that there should be a good clinical reason for performing any test or investigation.

“And as the authors of this new study note, the UK’s use of CT scans is lower than in countries without such legislation. It’s also important to remember that, even though the risks of brain tumours and leukaemia seemed to increase in people who had CT scans, these conditions are relatively rare: the overall effect was one extra case of leukaemia and one extra brain cancer for every 10,000 children who had a scan.”

Copyright Press Association 2012