UK study quantifies cancer risk from diagnostic X-rays

01/28/04

The most detailed calculation of its kind to estimate the risk of cancer from exposure to diagnostic X-rays is published in this week's issue of THE LANCET. It suggests that in the UK around 700 of the 124,000 cases of cancer diagnosed annually could be attributable to exposure to diagnostic X-rays.

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 González (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 them substantially.'

In an accompanying Commentary (p 340), Peter Herzog and Christina Rieger from Ludwig-Maximilians University Munich, Germany, state: "Berrington de González and Darby did not assess the indications or benefits achieved for patients in X-ray examinations. Benefits include the earlier detection of cancers by radiological examinations and the possibility of early treatment, which probably allows more cure of cancers than radiological exposure is able to cause". They conclude: "A general goal must be to avoid unnecessary X-ray procedures. Up to 30% of chest X-rays may not be indicated; unnecessary CT examinations can lengthen hospital stay as well as causing radiation exposure. In everyday practice, those ordering radiological procedures should think carefully about the benefit for and the risk to their patients for each examination."

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