Researchers said the risk of cancer caused by cumulative exposures to radiation in regular medical tests is growing in recent years, according to a study in the New England Journal of Medicine as quoted by news reports on Thursday.

Nearly 70 percent of more than 950,000 adult patients surveyed had at least one imaging procedure that exposed them to radiation doses double what would be expected from natural sources in the environment over a three-year period.

Low-dose radiation from medical imaging procedures has been linked to cancer, research lead author Reza Fazel said.

Doctors should prescribe the tests only when the benefits outweigh the risks, he said, adding while health-care workers are monitored to restrict their repeated contact with radiation, patients don't receive that same scrutiny.

"It sounds small, but when you translate it to the whole adult population, that's an estimated 4 million people getting high doses of radiation every year," Fazel said.

The study added more fuel to an ongoing debate over whether some doctors over-prescribe imaging tests to guard against patient lawsuits and to make money. Past researches have shown that doctors with ownership in imaging centers order 27 percent to 54 percent more CT scans, MRIs and stress tests than other doctors do.

Though the study included nearly a million people, the researchers said it is unclear to what extent the findings can be applied to the general population, including uninsured people who likely would get fewer imaging tests.

(Agencies via Xinhua August 27, 2009)