X factor

X-rays increase cancer risk

By Max Martin
Published: Monday 15 March 2004

x-rays, the largest human-made source of radiation exposure for the general population, are adding in hundreds of more cancer cases every year across the world, indicates a study published in The Lancet (Vol 363, No 9406, January 31, 2004). In the uk -- a country with stringent regulations for x-ray diagnostics -- 0.6 per cent of the cumulative cancer risk for people up to 75-year-old can be attributed to x-rays. This means about 700 cancer cases per year. The situation is worse in 13 other developed countries, for which estimates of the 'attributable risk' range from 0.6 to 1.8 per cent. In Japan, which has the highest annual exposure frequency in the world, the risk factor was found to be 3.2 per cent, implying 7,587 cancer patients per year (see table: Country-wise...).

The factors that were taken into account to gauge the risk included the average annual frequency of exposure for each type of diagnostic x-ray, age of the patients, estimates of the organ-specific radiation doses delivered by each x-ray type, cancer incidence rates and death rates due to different causes.

The effects of x-ray were found to be especially pronounced in children. "Our study shows that neonatal exposures (for children less than one year old) are responsible for three per cent of radiation-induced cancers, whereas kids aged 1-14 account for 19 per cent of the people at risk," explains Amy Berrington de Gonzlez of the Cancer Research uk, who co-authored the paper with Sarah Darby of the University of Oxford.

In the wake of the findings, should x-rays be shunned altogether? No. "If the treatment decision depends on the result of the x-ray, then it should be performed," says Gonzlez. The benefits of an x-ray outweigh the risks, as it helps doctors diagnose and monitor serious medical conditions. Moreover, studies conducted in the uk suggest that up to 30 per cent of chest x-rays taken in the country are not necessary, and so are some of the ct scans.

According to the researchers, exposure levels can be reduced in several ways without compromising the results. For instance, a new technology called digital mammography allows a better picture with a lower dose. Using such technologies is necessary -- Gonzlez and Darby found that frequency as well as dose of x-ray exposure influences the risk factor. The study showed that the number of cancer cases also depends on the irradiated organs, their sensitivity to radiation, and the age of those exposed to x-rays. ct scans were responsible for the largest number of cases of the nine listed cancers followed by barium enemas and hip and pelvis x-rays. The research suggests that a more careful use of the x-rays is the need of the day.

Country-wise cancer risk levels due to X-rays

Countries X-ray exposure per year
(per 1,000 population)
Attributable cancer risk
(in percentage)
Cancer cases**
(per year)
Australia 565 13 431
Canada 892 11 784
Croatia 903 18 169
Czech Republic 883 11 172
Finland 704 07 50
Germany 1,254 15 2,049
Japan* 1,477 32 7,587
Kuwait 896 07 40
Netherlands 600 07 208
Norway 708 12 77
Poland 641 06 291
Sweden 568 09 162
Switzerland 750 10 173
The UK 489 06 700
The US 962 09 5,695
*Number of CT scanners per million population in Japan is 37 times that for all health-care level 1 countries. If this number is reflected in annual frequency of CT examinations, then for Japan estimated annual number of X-rays per 1000 increases to 1573 and the attributable risk increases to 44%.
**Radiation-induced cancer risk
Source: ‘Risk of cancer from diagnostic X-rays: estimates for the UK and 14 other countries’, The Lancet, Volume 363, Number 9406, January 31, 2004

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