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THURSDAY, Jan. 29 (HealthDayNews) -- Diagnostic X-rays could be causing almost one of every 1,000 cases of cancer in the United States, British epidemiologists estimate.

That admittedly imprecise figure -- 0.9 percent of all American cancers -- comes from a study focused primarily on the United Kingdom, says study co-author Amy Berrington de Gonzales, an epidemiologist at the University of Oxford. The report appears in the Jan. 31 issue of The Lancet.

"Because of the large number of people exposed to diagnostic X-rays every year, even a very small risk to an individual from each X-ray could result in some cases of cancer being caused by these investigations," Berrington de Gonzales says. X-rays contribute 14 percent of total annual radiation exposure worldwide, the study authors note.

The study used "mathematical models based on the number and type of diagnostic X-rays performed every year and the doses of radiation that they deliver to estimate the number of cancers that might be caused in the U.K. and 14 other industrialized nations," she says.

The estimate for the U.K.: 0.6 percent of cancer cases, about 700 of the 124,000 cases diagnosed each year.

The estimate for the United States produced a deceptively precise number: 5,695 cancer cases each year, 0.9 percent of the total.

That is roughly twice the risk estimated in the last such study, done in 1981, according to the report, which adds a note of caution.

"This difference might be due to our detailed methods, although the U.S. estimate used cruder data than for other populations," the report says.

The caution is well-advised, says an American expert, G. Donald Frey, a medical physicist at the Medical University of South Carolina and a member of the Radiological Society of North America.

"This is a very difficult kind of study to do," Frey says. "There are very large uncertainties in the paper. You're talking about variations in numbers up to 50 percent, depending on the assumptions you make."

With that caution aside, "the United States came out very well," Frey adds. Only the United Kingdom, Poland (0.5 percent of cases; the Netherlands (0.7 percent) and Kuwait (0.7 percent) had lower numbers.

The figures for some other countries: Australia, 1.2 percent; Canada, 1.1 percent; Germany, 1.3 percent; Switzerland, 1 percent. The estimate for Japan was the highest, 2.9 percent.

What people should keep in mind, Frey says, are "the benefits from having these procedures."

"It is important for people to ask themselves if they are getting the best possible care rather than on concerns about the medical risk of a procedure," he says.

More information

For more on radiation, visit the National Institutes of Health or the U.S. Nuclear Regulatory Commission.

(SOURCES: Amy Berrington de Gonzalez, Ph.D., epidemiologist, University of Oxford, England; G. Donald Frey, Ph.D, medical physicist, Medical University of South Carolina, Charleston; Jan. 31, 2004, The Lancet)

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