The health risk posed by radiation from X-rays and other medical procedures is so small that it should not deter people from seeking needed medical care, according to a panel of senior scientists who examined the risks of low-level radiation.

Although the risks from such radiation are small, the panel assembled by the National Research Council also concluded that there is no dose of radiation, however low, that can be deemed completely safe.

Richard Monson, professor of epidemiology at the Harvard School of Public Health and the chairman of the science panel, said people should consult with their physicians before choosing optional medical services such as whole-body computerized tomography (CT) scans -- an increasingly popular diagnostic tool intended to detect medical problems at an early stage.

Monson was careful to say that there is no clear evidence that such scans, which subject people to about 100 times the radiation of a chest X-ray, are harmful. Rather, he said, people should follow the common-sense dictate of avoiding radiation whenever possible, especially when their physicians do not think such interventions are necessary.

The report is the seventh in a series of reports termed the Biological Effects of Ionizing Radiation being issued by the nation's premier science, engineering and medical advisory group, the National Academies.

Environmental advocates said the report's findings represent a victory because some pro-nuclear groups have advanced the argument that radiation below a certain low threshold is harmless or even beneficial.

The report said the best evidence suggests that even "the smallest dose has the potential to cause a small increase in risk to humans."

It estimates that the amount of radiation in about 10 whole-body scans, or about 1,000 chest X-rays, would result in a 1 percent risk of developing cancer if it were delivered all at once.

Monson and Ethel Gilbert, a biostatistician at the National Cancer Institute, said the report largely strengthens conclusions about the risks of cancer from radiation.

"From a public health point of view, prudence is a guideline," Monson said. "What is unnecessary radiation is up to the individual."

Daniel Hirsch, president of the Committee to Bridge the Gap, and Arjun Makhijani, president of the Institute for Energy and Environmental Research, both nonprofit advocacy groups, said the numbers identified by the report show that the risks of radiation and cancer are greater than previously thought and warrant strengthened regulation.

Paul H. Genoa of the Nuclear Energy Institute, however, said the report confirms long-held industry views about low-level radiation: "The risks are very small, and the current regulations are protective of public health and safety."