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http://edition.cnn.com/2003/HEALTH/04/01/health.xrays.reut/index.html

Study: Damage stays from low-dose X-rays

Tuesday, April 1, 2003 Posted: 1549 GMT (11:49 PM HKT)

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WASHINGTON (Reuters) -- Low doses of X-rays such as those patients receive in the dentist's chair may do more long-lasting damage than higher doses, German scientists reported on Monday in a study that turns common wisdom on its head.

Their findings, based on experiment with cell cultures, will have to be duplicated by other labs and then repeated in living animals before doctors can offer guidance on the effects of low-dose X-rays on humans.

The team, led by Markus Lobrich at the Universitat des Saarlandes, said its reasearch suggests that doses of X-rays generally considered harmless may in fact do long-lasting damage.

But they said they had developed a test that would help doctors look for genetic damage in people exposed to low doses of X-rays, such as cancer patients undergoing radiotherapy, patients getting X-rays and professionals working with X-ray equipment.

Writing in the Proceedings of the National Academy of Sciences, Lobrich's team said they exposed human cell cultures to varying X-ray doses in the laboratory.

To their surprise, they found that damage from low radiation levels lingered days to weeks longer than damage caused by more powerful levels.

Ionizing radiation like the kind produced by X-rays and some nuclear breakdown products can cause leukemia and other cancers. The radiation can cause breaks in DNA that go across both strands of its double helix structure.

Scientists had assumed that the body moves to repair these breaks at the same rate, no matter what the dose of radiation.

But Lobrich's team found this may not be true. It could be, they propose, that the body simply does not recognize lower levels of damage and does not move to repair it.

When these damaged cells divide and multiply, the unrepaired damage multiplies along with them, they suggested.

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