CHILDREN who undergo head scans triple their risk of developing leukaemia or a brain tumour, scientists warned today.
Medics often use the detailed imaging technique after accidents - for example when a child has received a blow to the head, to determine if there is a brain injury.
They are also frequently used to gauge the gravity of serious chest infections and other lung diseases.
However, researchers from Newcastle University say they should only be used when “fully clinically justified” due to the risk of triggering cancer.
In a study published today (Thursday) in The Lancet, they found those who received two or three CT head scans before 15 were three times more likely than the child population as a whole to develop brain cancer over the next decade..
Those who received five to 10 body scans were at triple the risk of developing leukaemia over that timescale. Head CT scans tend to involve higher radiation doses than body scans.
Dr Mark Pearce, from Newcastle University, said: “CT scans are very useful but they have relatively high doses of radiation, particularly when compared to x-ray. They have about 10 times the dose used in x-ray.”
While the “immediate benefits” usually outweighed the long-term risks, he said reducing radiation doses used in CT scans “should be a priority”.
He also stated that although CT scans tripled the relative risk of these childhood cancers, the absolute risk of developing them was still "very small".
He and co-author Professor Sir Alan Craft calculated that for every 10,000 children under 10 who received a single head CT scan, one extra brain tumour case and one extra leukaemia case would result over 10 years.
Among all under 20s, the baseline risk of brain tumour is 0.3 per 10,000 over 10 years, while it is 0.45 per 10,000 for leukaemia.
The study results were based on 180,000 youngsters who underwent CT scans in Britain between 1985 and 2002.
Dr Kieran McHugh, from Great Ormond Street Hospital, noted that radiation doses used in CT scans were now lower than in the past “and therefore the cancer risk is a lot less”.
Professor Malcolm Sperrin, director of medical physics at the Royal Berkshire Hospital in Reading, said CT scans "will only be conducted when the risk from the underlying condition is itself serious and that there is a greater risk to life by not having the scan at all".
He added that rules governing their use were "particularly stringent" in Britain.