Study finds CT scans create a small risk of blood cancer in young people - but benefits cannot be overlooked


A MAJOR study has shown CT scans create a small risk of blood cancer developing in young people -  but the benefit of such scans in a patient’s diagnosis and treatment cannot be overlooked.

The study of almost one million individuals found an association between exposure to radiation from computerised tomography (CT) scans in young people and an increased risk of blood cancers.

The findings of the European-funded EPI-CT study, reported in Nature Medicine, said CT scans, which use x-rays and a computer to create detailed images of the inside of the body, while largely beneficial, entail a small risk that needs to be minimised as much as possible.

This is the main conclusion of the study, led by the Barcelona Institute for Global Health (ISGlobal). Study author Magda Bosch de Basea Gomez, an ISGlobal researcher, said in terms of absolute risk, for every 10,000 children who have a CT scan, around 1-2 cases of cancer in the 12 years following the examination can be expected to be seen.

‘Benefits outweigh risks’

The study acknowledged the benefits of CT imaging in patient management, for diagnostic efficacy, treatment planning and follow-up, are undisputed.

Dr Sarah McQuaid, Chair of IPEM’s Nuclear Medicine Special Interest Group, said: ‘This publication indicates there could be a small cancer risk from CT scans in young people, but it is important for this to be viewed in the context of the substantial benefit these scans bring, due to the important diagnostic information they provide.

‘Legally, a medical scan involving ionising radiation can only be justified if the benefits outweigh the risks, and so the number of patients whose medical care will have been improved from these CT scans will have been very high, and lives undoubtedly saved as a result. 

‘As the authors [of the study] comment, any risks can be reduced further by optimising radiation doses, so that no more dose is given than is necessary. Medical physicists in research and hospital settings work to ensure this is the case, and there have been substantial improvements in CT scans, and therefore patient doses, over the years.

‘With continued efforts in this area risks can be reduced even further, and this remains an important part of medical physicists’ roles.’

Bringing together expertise

IPEM Fellow Jim Thurston, a radiation protection expert, and IPEM Member Professor Peter Marsden, a medical physics expert, in a joint statement said healthcare outcomes for patients have benefited greatly from CT scans.

They said: ‘The risk of malignancy from exposure to ionising radiation, such as the x-rays used in CT scans, has long been understood by healthcare professionals, and is a significant factor in the justification of using CT as a diagnostic tool for every single individual patient, especially children, adolescents and young adults. Justification essentially requires that the benefit of carrying out the CT scan in terms of the images leading to a diagnosis and therefore to treatment, outweighs the risks from the scan, including from the radiation dose received.

‘Similarly, the optimisation of CT scanners to achieve those clear diagnostic outcomes for the lowest possible dose, is an established and important part of the procedure, bringing together the expertise of specialist clinicians, radiographers and medical physicists to achieve.’

Significant contribution to understanding

They added: ‘The authors of this paper report their findings of an association between the cumulative dose to active bone marrow from CT scans and an excess risk of haematological malignancies in children, adolescents and young adults. The study is based on over 1.3 million scans of almost 900,000 patients across nine European countries.

‘As such this paper makes a significant contribution to the understanding of the effects of ionising radiation, specifically x-rays, on the human body at the levels of radiation exposure encountered in diagnostic CT procedures.

‘Their findings reinforce the modelling of risk, which historically has been based on extrapolation of risk from significantly higher radiation exposures such as those received by the survivors of the atomic bombs at Hiroshima and Nagasaki, down to the much lower doses received by patients from CT scanning. The advances in data management and sharing have enabled lower exposure studies to gain the necessary statistical significance.

‘The finding of this paper indicate levels of risk which align with those currently estimated and do not suggest that the use of CT carries a greater risk than previously thought.

‘The paper very clearly lends justification to the work of healthcare professionals, including medical physicists, in ensuring radiation exposure of patients is kept as low as reasonably practicable in the diagnosis of disease.’

Importance of controlling exposure

IPEM Fellow Professor Malcolm Sperrin said: ‘It has been known for many decades that there is a link between exposure to ionising radiation and the generation of cancers.  There has been a huge amount of work from centres around the world to calculate the risk factor and how the risk manifests itself in terms of type of disease.

‘This has been the central tenet for not just limiting exposure to ionising radiation but also for providing justification for each and every patient; specifically, the benefit must outweigh any potential detriment. 

‘This study confirms the importance of controlling exposure and furthermore states a risk factor which is of importance when estimating the risk/benefit balance. The study is well designed, comprehensive and a valuable addition to the body of knowledge.’

Nature Medicine article