Low radiation levels pose cancer risk

Scientists say no threshold below which exposure is harmless

Kevin Rivoli / AP file

Kodak research associate Phillip Bunch looks over a new X-ray film which cuts a patient's radiation exposure by about 50 percent, while in an office in Rochester, N.Y. A typical single chest X-ray accounts for 0.1 millisievert, average background radiation.

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updated 6:29 p.m. ET July 7, 2005

WASHINGTON - Even very low doses of radiation pose a risk of cancer over a person’s lifetime, a National Academy of Sciences panel concluded. It rejected some scientists’ arguments that tiny doses are harmless or may in fact be beneficial.

The findings, disclosed in a report Wednesday, could influence the maximum radiation levels that are allowed at abandoned reactors and other nuclear sites and raises warnings about excessive exposure to radiation for medical purposes such as repeated whole-body CT scans.

“It is unlikely that there is a threshold (of radiation exposure) below which cancers are not induced,” the scientists said.

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While at low doses “the number of radiation-induced cancers will be small ... as the overall lifetime exposure increases, so does the risk,” the experts said.

Even common X-rays pose some risk of adverse health effects, the scientists found, although the panel said there was not enough information available to accurately estimate the cancer risk from X-rays. Nevertheless, the report said, there is evidence that per unit of absorbed radiation, X-rays may be more dangerous than other radiation.

The panel also said that approximately one person out of 1,000 would develop cancer from exposure to the amount of radiation from a single, average whole body CT-scan.

But the report should not scare people away from nuclear medicine, said Dr. Henry Royal, a professor of radiology at Washington University in St. Louis. He said most often the benefits of such tests and treatments outweigh the risks.

But Royal also said that procedures such as CT scans should be used to deal with a specific medical problems and not part of annual medical screenings. “You should not be exposed to radiation for superficial reasons,” Royal said in a telephone interview.

Scientists for years have debated how extremely low doses of radiation affect human health.

Pro-nuclear advocates, as well as some independent scientists, have maintained that the current risk models for low-level radiation has produced more stringent requirements than is necessary to protect public health.

It is an issue in determining decontamination requirements at abandoned reactors and at federal weapons sites.

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