Scientists estimate cancer risk from X-rays, less than 2 percent in most countries

Friday, January 30th 2004, 12:00 am
By: News On 6

LONDON (AP) _ The risk of cancer from common X-rays and increasingly popular CT scans ranges from less than 1 percent to about 3 percent, according to a new study.

The small risk posed by X-ray radiation is well-known, but the study by researchers from Oxford University and Cancer Research U.K. makes the most careful effort to date to estimate it precisely, the scientists said.

CT scans, also known as CAT scans, are computer-enhanced X-rays that can provide a better view of all parts of the body. But they emit significantly more radiation than a standard X-ray.

In the United States, doctors have urged caution about unnecessarily using the scans on children. Children are more sensitive to radiation and exposure is cumulative.

The new research indicates the cancer risk _ ranging from 0.6 percent to 3.2 percent _ varies depending on the frequency of X-rays and scans in 15 countries surveyed. Experts not involved in the study wrote in the journal The Lancet, which published the findings, that the benefits of X-rays and CT scans far outweigh the risk.

Of the 15 countries surveyed, the cancer risk believed linked to X-rays was lowest in Britain, where they are used least frequently. They estimated that 0.6 percent of the cumulative British cancer risk for those under 75 years old came from X-ray exposure, accounting for about 700 of the nation's 124,000 annual cancer diagnoses.

The American figure nearly doubled a 1981 estimate that about 0.5 percent of U.S. cancer cases were linked to X-rays. The new 0.9 percent estimate translates into 5,695 cases per year, the researchers said

The highest risk was in Japan, where X-rays are done much more frequently and accounted for 3.2 percent of cancer risk, or 7,587 cases per year, wrote the researchers, Amy Berrington de Gonzalez of Cancer Research U.K. and Sarah Darby of Oxford.

Dr. Peter Herzog and Dr. Christina Rieger, of Ludwig-Maximilians University in Munich, Germany, noted in a separate Lancet piece that the researchers did not assess the benefits of X-rays and CT scans.

``Benefits include the earlier detection of cancers ... and the possibility of early treatment, which probably allows more cure of cancers than radiological exposure is able to cause,'' they wrote. Herzog and Rieger were not involved in the study.

In all the other countries for which Berrington de Gonzalez and Darby analyzed data, they estimated that X-rays accounted for less than 2 percent of the cancer risk _ 0.9 percent in Sweden, 1.3 percent in Australia, 1.1 percent in Canada and the Czech Republic, 1.8 percent in Croatia, 0.7 percent in Finland, 1.5 percent in Germany, 0.7 percent in Kuwait and the Netherlands, 1.2 percent in Norway, 0.6 percent in Poland, and 1.0 percent in Switzerland.

Dr. Adrian Dixon, radiology professor at Cambridge University, said the estimates were not surprising and the risk posed by X-rays was relatively small compared to the overall chance of getting cancer.

``I don't think (people) should be worried at all,'' he said. ``You shouldn't be having an X-ray unless the benefits are greater than the harm and that's why we vet every request fairly carefully.''

All the rates cover only cancer diagnoses in people under age 75, since data for cancer incidence among those over 75 was unavailable in all 15 countries, the researchers said.

They based their estimates on the incidence of cancer in each country, the national rates of X-ray and CT scan use between 1991 and 1996, the most recent years for which data were available, and mathematical models of the links between radiation exposure and cancer.

They said that while their model may have overstated the risk, they believed they had not significantly understated it.

While any individual's risk of developing cancer because of an X-ray was tiny, the widespread use of X-rays and CT scans means the risks translate into a significant number of cases, the researchers said.

They said reducing the radiation dose delivered by each X-ray or CT scan and cutting the frequency of use could lessen cancer risks.

Herzog and Rieger, the outside commentators, noted that development of lower-radiation scanning equipment had already reduced the risk and was likely to continue to do so. They agreed with the researchers that doctors should avoid unnecessary X-rays and CT scans.