Diagnostic X-rays (used in conventional radiography and imaging techniques such as computed tomography [CT]) are the largest man-made source of radiation exposure to the general population, contributing about 14% of the total annual exposure worldwide from all sources. Although diagnostic X-rays provide great benefits, it is generally accepted that their use is associated with very small increases in cancer risk.

Amy Berrington de Gonzlez (University of Oxford, UK) and Sarah Darby (Cancer Research UK) have estimated the likely extent of the cancer risk based on the annual number of diagnostic X-rays undertaken in the UK and in 14 other developed countries (Australia, Canada, Croatia, Czech Republic, Finland, Germany, Japan, Kuwait, the Netherlands, Norway, Poland, Sweden, Switzerland, and the USA).

The investigators estimate that in the UK about 0.6% of the cumulative risk of cancer to age 75 years may be attributable to diagnostic X-rays - equivalent to around 700 cancer cases annually. The proportions of cases attributable to diagnostic X-ray exposure in other industrialised countries for which data were available varied from 0.6 -1.8% and over 3% in Japan (the country with the highest estimated annual diagnostic X-ray use in the world). The UK's estimates were among the lowest because the annual frequency of diagnostic X-ray exposure was lower than in the other countries studied.

The authors conclude: 'Our calculations depended on a number of assumptions, and so are inevitably subject to considerable uncertainty. The possibility that we have overestimated the risks cannot be ruled out, but it seems unlikely that we have underestimated
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Contact: Joe Santangelo
j.santangelo@elsevier.com
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Lancet
29-Jan-2004