Too Much Radiation From Medical Imaging?

Researchers Say Patients Need to Weigh Risks vs. Benefits of Imaging Tests

By Salynn Boyles
WebMD Health News

Reviewed By Louise Chang, MD

Aug. 26, 2009 -- As many as 4 million adults in the U.S. under the age of 65 are being exposed to high, potentially cancer-causing levels of radiation from medical imaging tests of unproven value, according to a new government-funded study.

Analysis of insurance claims for close to 1 million non-elderly adults found that roughly two-thirds had at least one medical imaging test resulting in radiation exposure and one-fifth were exposed to moderate-to-high doses of radiation during the study period.

Nuclear imaging (often done to check for heart disease) and computed tomography (CT) scans delivered the most radiation.

An earlier study in 2007 estimated that as many as 2% of cancers in the U.S. are caused by radiation exposure from CT-related imaging alone.

The new study appears in this week's New England Journal of Medicine.

"We don't want to scare people and have them refuse necessary procedures, but physicians and patients need to be aware that radiation is not benign," study researcher Reza Fazel, MD, of Atlanta's Emory University School of Medicine, tells WebMD. "Our study shows that a lot of people are getting high doses of radiation."

Government estimates suggest that per capita radiation doses in the U.S. have risen sixfold since the early 1980s as a result of greater utilization of medical imaging tests performed to diagnose and monitor a wide range of diseases.

The study shows that:

  • CT scans and nuclear imaging accounted for three-fourths of radiation exposure, with nuclear stress tests, also known as myocardial perfusion imaging, identified as the procedure accounting for the largest single radiation exposure.
  • The highest radiation exposures occurred among women and older adults.
  • Imaging-associated exposures among young adults were not insignificant. Thirty percent of men and 40% of women with high exposure per year in the study were under the age of 50.
  • 80% of radiation exposures occurred among non-hospitalized patients.

Radiation exposure is commonly measured in millisieverts (mSv). The average person in the U.S. can expect to receive no more than 3 mSv of exposure per year from naturally occurring background radiation. An exposure of greater than 20 mSv is considered high, while greater than 3 mSv to 20 mSv is considered moderate.

Myocardial perfusion imaging for heart disease delivers about 15 mSv per test.

Value of Some Medical Imaging Unclear

In a perspective published with the study, cardiologist Michael S. Lauer, MD, of the National Heart Lung and Blood Institute (NHLBI) presented the hypothetical case of a 58-year-old man named Jim with risk factors for heart disease who has an inconclusive nuclear stress test followed by another commonly used imaging test known as CT angiography, which also fails to confirm his diagnosis.

The two tests would result in more than 20 mSv of radiation exposure.

"Jim's story reflects outpatient practice that has become increasingly common in the United States, which has the world's highest per capita imaging rate," Lauer writes.

"Most physicians who order imaging tests experience no consequences for incurring costs for procedures of unproven value. On the contrary, they or their colleagues are paid for their services, and their patients don't complain because the costs are covered."

While health care reform has the potential to slow the growth of medical imaging, Lauer says the real challenge is to identify which tests add value for the diagnosis and management of disease and which do not.

He tells WebMD that for some tests, like mammography, the benefits are clear. But for others, like nuclear stress testing to identify heart disease, the risks may very well outweigh the benefits.

"Medical practice should be based on the most rigorous science, and we don't have that for many of these tests," he says. "We need large, well-designed trials to figure this out."

SOURCES: Fazel, R. New England Journal of Medicine, Aug. 27, 2009; vol 361: pp 849-857. News release, National Heart Lung and Blood Institute. Reza Fazel, MD, MSc, division of cardiology, department of medicine, Emory University School of Medicine. Michael S. Lauer, MD, National Heart Lung and Blood Institute. Brenner, D.J. New England Journal of Medicine, Nov. 29, 2007; vol 357: pp 2277-2284. NCRPM: "Ionizing Radiation Exposure of the Population of the United States," March 2009.

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