Tue Feb 11, 5:22 PM ET

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By Maggie Fox, Health and Science Correspondent

WASHINGTON (Reuters) - A panel of experts on Tuesday affirmed a report that said nuclear fallout from atmospheric atomic bomb tests reached virtually every part of the United States, causing at least 11,000 cancer cases over 50 years.

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The panel appointed by the independent National Research Council (news - web sites) said the report, which was not officially published when it was issued nearly a year ago but is nonetheless widely available, was put together carefully and needed just a few adjustments.

The atmospheric bomb tests were carried out mostly between 1951 and 1962, and kicked radioactive dust up thousands of feet into the air, where it was carried literally around the world.

For decades, various groups have expressed fears that the fallout caused many cases of cancer, and government attempts to reassure people have had little success.

The report was compiled by the Centers for Disease Control and Prevention (news - web sites) and the National Cancer Institute (news - web sites) at the request of Congress. It followed previous studies which had largely focused on the effects of radioactive iodine, called iodine-131, which is linked with thyroid cancer.

Radioactive materials can build up in the body and cause cancer. The biggest risk is to people who eat meat and milk, because cattle eat the fallout when they graze and over years it builds up in their bodies.

Children are at the highest risk because they are so small and because their thyroid glands, where radioactive iodine tends to build up, are so active.

Congress, led by Iowa Senator Tom Harkin, a Democrat who lost four of his six siblings to cancer, asked the National Research Council if the report might have missed something and whether a broader study, looking at other radioactive materials such as strontium and cesium, should be carried out.

Sharon Friedman, an expert in risk communication at Lehigh University in Bethlehem, Pennsylvania, who helped conduct the review of the original report, said a broader study would not be feasible.

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"We decided it wouldn't yield much information because the base data were bad," Friedman said in a telephone interview. The government at the time did little to keep track of who might be affected by the fallout.

"When these bombs were being tested above ground, there were less than 100 sites in the United States that actually measured what the radioactive fallout was -- and they were scattered willy-nilly across the country," she added.

Her committee's review said the original report assumed that any exposure to radioactive materials at all was likely to cause harm.

"We think it was very competently done. There are a few things to be fixed here and there," she said.

The original report said that anywhere between 11,000 and 200,000 extra cancer cases were likely to have been caused by fallout over 50 years.

This compares to 40 million overall cancer deaths over the same period. An American has a 20 percent risk of developing cancer over his or her life, and the fallout raises that risk to 20.03 percent, the report said.

Friedman said statistical analysis showed that the lower numbers -- closer to 11,000 cases -- were more accurate and thus more likely.

"It's a very low probability," she said. Effects from strontium and cesium were likely to have been negligible.

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