CHICAGO (AP) -- Use of high-tech imaging scans in older cancer patients has climbed substantially in recent years, a study found, raising concerns about costs and radiation exposure.

For example, lung cancer patients diagnosed in 2006 had on average almost six CT scans in the next two years, versus four scans for those diagnosed in 1999.

The tests examined include CT scans and PET scans, which both expose patients to more radiation than standard X-rays. They are increasingly being used for other illnesses besides cancer and to detect injuries.

Whether they are being overused in cancer patients is uncertain. Duke University researcher Dr. Kevin Schulman, a study author, said money might be a driving factor because Medicare reimburses doctors more for analyzing the scans than for less complex tests. Hospitals and doctors offices equipped with scans also get relatively generous Medicare reimbursements for using the technology.

While these sophisticated scans typically provide more detailed images than conventional X-rays, the study didn't look at whether their increasing use has improved cancer patients' survival. Some small studies have suggested the scans can improve treatment but evidence is lacking on how they affect survival.

Eric Hoffman, a spokesman for the Access to Medical Imaging Coalition, a group representing scan makers, argued that high-tech scanning has improved longevity in cancer patients. He cited industry-sponsored research suggesting that the scans have contributed to a decline in the nation's cancer death rate.

The new study involved 1999-2006 Medicare claims for about 100,000 newly diagnosed cancer patients aged 76 on average. Results appear in Wednesday's Journal of the American Medical Association.

Patients diagnosed with lung cancer or lymphoma in 2006 had the largest imaging costs, exceeding an average of $3,000 per patient within two years.

Without knowing why the tests were performed or how they affected patient outcomes, "it's hard to say whether this represents a good or bad use of taxpayer dollars," said Dr. Jane Weeks, a health outcomes researcher at Dana-Farber Cancer Institute. She was not involved in the study.

Costs of using these tests in cancer patients has increased at a rate outpacing total cancer care costs in Medicare patients. Schulman said that's because the tests are getting more expensive and more are being done.

Radiation from imaging scans can cause cancer many years later, so any excessive amount is worrisome, although perhaps less so in older people because these secondary cancers take so long to develop, Schulman said.

Overall, the use of PET scans climbed most dramatically, a 6-fold to 14-fold increase depending on specific cancer type. Medicare began covering these exams for cancer patients during the study period; they involve injecting a radioactive material to detect location and activity of cancer cells. They typically use the same type of sophisticated X-ray imaging used in CT scans, and can cost more than $2,000 or about double the cost of CT scans.

In some cases, CT scans and PET scans deliver hundreds of times the amount of radiation in a single conventional X-ray.

Dr. Allen Lichter, CEO of the American Society of Clinical Oncology, said PET scans provide valuable information, like whether a lymph node is swollen from an infection or cancer, and that it is not surprising their use has increased.

He said the study underscores the importance of research to determine if the increases are warranted, "so we can sort this out with science instead of conjecture."

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