In 2012, two major studies were published about the risks of ionising radiation from imaging. Pearce and colleagues’ study in The Lancet examined the excess risk of leukaemia and brain tumours for children and adolescents exposed to computed tomography (CT) scans. They found that children exposed to cumulative doses of 50mGy (3-5 CTs) may have triple the risk of leukaemia, and doses of 60mGy may have almost triple the risk of brain tumours.
In addition, the Pijpe and colleagues’ GEN-RAD-RISK paper in the BMJ study showed that women such as Angelina Jolie who carry a specific mutation associated with breast cancer (BRCA1/2), and who were exposed to diagnostic radiation before the age of thirty, had almost twice the risk of breast cancer (with a dose-response pattern). This study involved lower doses, which we have previously considered fairly ‘safe’ (e.g. 4mGy from a single mammogram or shoulder X-ray).
On the basis of these studies, we wrote a blog post and started writing an editorial for the British Journal of Sports Medicine. While we were in the final stages of preparing the editorial, a third study was published. The Matthews et al Australian data linkage study, with an enormous cohort (11 million) showed that the adjusted overall cancer incidence for young people exposed to a CT scan was twenty-four percent greater than for those who were not exposed.
That is, one in every 1800 scans resulted in an excess cancer case. As the mean follow up time was only 9.5 years (relatively short in relation to the time taken to develop cancer), this suggests the true lifetime risk may be much higher. We await with interest the relative risk in older people to see whether the risks for the young also apply to those in middle age.
We’ve known about the risks of radiation for some time, but these three studies quantify the risks. Essentially, they show that relatively low doses of ionising radiation, previously considered ‘safe’ can translate into excess cancer cases.
We believe that these findings call for a change in imaging practice. First, ionising radiation should be a consideration for the referring doctor when deciding whether a patient needs a scan (and if so, what type). Second, imaging techniques and machines that reduce ionising radiation doses should always be used. Finally, government funding models must be reviewed to ensure there are no inappropriate incentives towards a radiating scan.
For example, in Australia, if a young patient presents to a GP with low back pain and the GP orders a scan, Medicare would fund a CT scan but not a magnetic resonance imaging (MRI), even though this may be a safer alternative in terms of radiation.
The body of evidence is growing. We need to start translating evidence into practice, just as we did when it was discovered CT scans and X-rays should not be performed on pregnant women. Doctors can look back on scans that they ordered in the 1990s and 2000s and argue, justifiably, that they were following best practice at the time when they ordered a CT or SPECT bone scan.
From 2013, doctors who order a scan which involves ionising radiation in a young athlete would need to be able to argue that they understood the specific increased risk of cancer from these recent papers and felt that the need to get information from that specific scan outweighed that increased risk.
The days of ordering, say a CT scan to work out whether a teenage runner has a slight leg length discrepancy and might need a 3mm heel lift in one shoe, should be over as of the publication of these cancer linkage papers.
This CSM4ed blog is a forum for your opinions and questions. Feel free to comment on Twitter (@CSM4ed) or email us directly via david.adams at hiphealth.ca.
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Jessica Orchard is a Project Officer in the Cardiovascular Division and an Adjunct Lecturer in the School of Public Health, University of Sydney, Australia. With tertiary qualifications in economics, law and public health, she also has extensive research experience in sports injury epidemiology and prevention.
John Orchard is a sports physician, injury researcher and team doctor. He is an Adjunct Associate Professor in the School of Public Health, University of Sydney, Australia.
1. Pearce MS, Salotti JA, Little MP, et al. Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort study. Lancet 2012;380(9840):499-505
2. Pijpe A, Andrieu N, Easton D, et al;. Exposure to diagnostic radiation and risk of breast cancer among carriers of BRCA1/2 mutations: retrospective cohort study (GENE-RAD-RISK). BMJ 2012;Sep 6(345):e5660
3. Orchard J, Orchard J, Grenfell T, et al. Ionising radiation: three game-changing studies for imaging in sports medicine (editorial). British Journal of Sports Medicine 2013;[online first: 10.1136/bjsports-2013-092499]
4. Mathews J, Forsythe A, Brady Z, et al. Cancer risk in 680 000 people exposed to computed tomography scans in childhood or adolescence: data linkage study of 11 million Australians. BMJ 2013;346:f2360