With MRI scans becoming cheaper and more common, perhaps the days of the CT scan that does a similar function using X-Rays rather than magnetic fields, are numbered. A report shows that the cancer risk from CT scans, especially Brain Cancer and Leukemia can triple in some cases.

The Article published in The Lancet, and written by Dr Mark Pearce and Professor Sir Alan Craft, Newcastle University, UK; Professor Louise Parker, Dalhousie University, Halifax, NS, Canada; Dr Amy Berrington de González, National Cancer Institute (NCI), National Institutes of Health (NIH), Bethesda, MD, USA, and colleagues, represents the culmination of almost two decades of research in this area, and is jointly funded by the UK Department of Health and NCI/NIH.

It shows that 2 or 3 computed tomography (CT) scans of a child’s head (child meaning under 15 years old in this case), can triple the risk of brain cancer. The total dose of radiation would be around 60mGy, while 5 to 10 scans giving a dose of some 50mGy or more, triples the risk of leukemia.

The researchers go on to point out that the risks are still miniscule as the diseases are not particularly common, thus an increased risk is far from absolute certainty of contracting the disease. The CT scan is a useful and sometimes necessary diagnostic tool, and therefore physicians must weigh the risks and make patients and their parents aware.

The retrospective study used records from the radiology departments of some 70% of the UK’s hospitals, and gathered data from 180,000 patients who underwent CT scans between 1985 and 2002. By looking at the number and types of CT scan from the records, the researchers estimated the dose absorbed in milli-Grays (mGy) by the brain and bone marrow in patient for each scan. The data was then cross-checked with cancer incidence and mortality reports in the UK National Health Service Registry between 1985 and 2008. It was then possible to show if a person having scans was more likely to develop cancer. From this, they calculated excess incidence of leukemia and brain tumors.

The UK has relatively low usage of CT scans due to a nationalized health service and the Ionising Radiation (Medical Exposure) Regulations, that make sure scans are only done when medically justified.

Lead author Dr Pearce says:

“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 …

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.”

Rosies ct scan
A patient undergoes a CT scan

In a linked Comment, Dr Andrew J Einstein, New York Presbyterian Hospital and Columbia University Medical Center, New York, NY, USA, says:

“This study should reduce the debates about whether risks from CT are real, but the specialty has anyway changed strikingly in the past decade, even while the risk debate continued. New CT scanners all now have dose-reductions options, and there is far more awareness among practitioners about the need to justify and optimise CT doses, an awareness that will surely be bolstered by Pearce and colleagues’ study …

Pearce and colleagues confirm that CT scans almost certainly produce a small cancer risk. 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.””

Written by Rupert Shepherd