June 7, 2012

expert reaction to new research into radiation from CT scans in childhood and subsequent risk of leukaemia and brain tumours

The Lancet published a study showing radiation exposure received from 2 to 3 CT scans of the head in childhood could triple the risk of later developing brain cancer, while around 5 to 10 such scans could triple the risk of developing leukaemia.

Prof David Spiegelhalter, Winton Professor Of The Public Understanding Of Risk, University of Cambridge, said:

“This study suggests there is around a 1 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 judgement has to be made.”

Prof Malcolm Sperrin, Director of Medical Physics at Royal Berkshire Hospital, said:

“It has been known for many years that exposure to ionising radiation may manifest itself as a cancer later in life. However, it is also embedded in law in the UK that exposure to ionising radiation must be kept as low as possible bearing in mind the intended use of techniques such as CT. It is necessary to understand that CT scans as well as other uses of X-rays 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. Different countries manage the risk in different ways but the UK is particularly stringent in its controls and guidance which recognises risk but also recognises the unquestioned benefit. It should also be borne in mind that the natural background radiation from radon etc produces an annual dose of typically 2.5mSv and that overall the risk from radiation is negligible in comparison to numerous other risks especially that from smoking, drinking etc, and also from everyday activities such as from crossing roads.

“The study and its conclusions seem to be reasonable in their approach although identifying and allowing for the multitude of factors leading to a health outcome is very difficult to achieve. The paper does reasonably conclude that further studies are necessary and that overall the findings do add to the body of knowledge.”

Prof Richard Wakeford, Visiting Professor, Dalton Nuclear Institute, University of Manchester, 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. This means that large studies of many people are needed to detect this presumed radiation risk against the background risk from other factors, and this is what this large CT scan study has achieved. The radiation risks the study has detected are at the level currently assumed for the purposes of radiation protection, i.e. small, which is reassuring. However, as with all sources of radiation exposure, this small risk should be taken into account when radiation is used.”

‘Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort study’ by Pearce et al., published in The Lancet on Thursday 7 June.