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Are We Being Overexposed?

As Americans take more imaging tests, how much radiation is too much? And at what cost?

Debbie Liebross describes herself as a bit of “a cancer phobic.” And she has reason to worry. Her mother died of lung cancer at age 69, and Liebross was once a social smoker, although she kicked the habit early.

To keep anxiety at bay, the 55-year-old resident of Fort Lauderdale, Fla., has gotten a chest x-ray every few years for at least a decade to check out her lungs. Last year, when her family doctor suggested a baseline CT (computed tomography) scan of her heart to identify any developing problems, she decided to get her lungs scanned as well.

Thousands of Americans like Liebross undergo imaging tests each day without hesitation. Costly medical imaging has become increasingly—and sometimes unnecessarily—commonplace. As a result, Americans today are exposed to seven times more radiation, via medical tests, than they were in the early 1980s, according to a report released this spring by the National Council on Radiation Protection and Measurements.

“People can be exposed to a large amount of radiation,” says Timothy Bullard, M.D., an emergency room physician in Orlando, Fla., who has studied radiation exposure in patients. “They don’t realize it. Nor do the physicians. We don’t have any good way of tracking it right now.”

A variety of influences have boosted Americans’ exposure to imaging radiation—from physician malpractice fears to aggressive marketing of body scans, virtual colonoscopies, and other painless screening tools.

But when radiation exposure is involved, how much is too much? And how does one weigh relative risks and benefits, particularly in light of proliferating imaging options?

A study published Aug. 27 in the New England Journal of Medicine, looking at nearly 1 million patients ages 18 to 64 over a three-year period, found that radiation exposure from medical imaging tests can leave the body with higher cumulative doses than previously thought. Nearly seven out of every 10 adults—69 percent—had gotten at least one imaging scan during that period. The oldest in the group, ages 55 to 64, were most likely to have higher doses. The study estimates that at least 4 million Americans are exposed to high doses of radiation each year from medical imaging tests.

The study’s findings, and those of previous studies, point to “tens of thousands of cancers” related to medical imaging, says Rita Redberg, M.D., a medical imaging researcher at the University of California, San Francisco, who is not connected to the study.

Individual risk depends on the number and the types of scans, as well as the age at which the exposure begins, Redberg says. Malignancies can take a number of years to develop.

Patients who have had a number of CT scans—tests that produce cross-sectional images of the body—are most at risk.

“I would be more concerned if you’ve had a number of CT scans—definitely,” says Redberg. “The idea is you want to limit your lifetime radiation exposure.”

Cancer risks, imaging costs

The average radiation dose per American from all sources, including background radiation, rose from 3.6 to 6.2 mSv (millisieverts) from the early 1980s to 2006—primarily due to imaging tests, according to the council’s findings.

Another report, published last year by the Government Accountability Office, focused on the price tag. From 2000 through 2006, Medicare spending for imaging slightly more than doubled, reaching $14 billion. When experts discuss reducing wasteful spending in Medicare, unnecessary imaging is often toward the top of the list. The spending for some of these tests increased significantly faster than x-rays and ultrasound.

Imaging tests can play a crucial role in diagnosing cancer, heart blockages, and other diseases. Before agreeing to any test, however, patients should weigh the risks and benefits of their particular situation, physicians advise.

Luckily, as adults age, the very small cancer risk associated with radiation exposure gets even smaller, says David Brenner, director of the Center for Radiological Research at Columbia University Medical Center. It takes most radiation-induced cancers 10 to 20 years to develop in adults, says Brenner, one of the country’s foremost authorities on low-dose radiation and cancer risk. Older adults are more likely to have medical problems that can be identified by a CT scan or another test, he says, but “you don’t want to have a CT scan unless there is a very good reason for doing so.”

Other top experts agree.

“In a way, the worst radiation exposure is from a test that wasn’t necessary in the first place,” says James Thrall, M.D., chair of the board of chancellors at the American College of Radiology. “That’s just a tragedy. What compounds the tragedy is it’s going to cost the individual money on top of the unnecessary radiation exposure. And it’s going to cost society money.”

What’s driving many tests

Experts say physicians are prescribing more imaging tests. They point specifically to “physicians with a financial stake in [imaging] facilities who refer patients to those facilities,” says David Schauer, executive director of the National Council on Radiation Protection and Measurements. Indeed, physicians who own their own imaging equipment are more likely to order imaging tests than other doctors, according to a report in June by the Medicare Payment Advisory Commission.

As part of health care reform legislation, Congress is considering a measure that would prohibit doctors from referring their own patients to their imaging machines. Currently doctors are barred from referring Medicare patients for services in which they have a financial interest, but CT scans are exceptions.

In a study last year, Stanford University’s Laurence Baker found that each new CT scanner in service prompted an additional 2,224 CT tests per year, adding $685,000 to Medicare costs.

But financial interest isn’t the only driving force behind the growing number of tests. So is defensive medicine, to some degree. One out of every five x-rays and 28 percent of all CT scans are ordered because of malpractice fears, according to the Massachusetts Medical Society, which surveyed 850 doctors.

But even as the number of tests increases, clinicians are not necessarily savvy about the degree of radiation involved, which can range from lower levels with x-rays and mammograms to higher levels with CT scans and barium enemas. In a recent survey involving physicians at a teaching hospital, nearly 63 percent underestimated the radiation exposure of an abdominal CT scan. And just 20 percent said they discussed radiation with patients.

FDA warnings

Marketing also can spur demand. The Food and Drug Administration advises against full-body scans for patients who have no symptoms. It says the risks related to radiation and unnecessary follow-up tests outweigh any potential benefits. In May, federal officials decided that Medicare should not cover virtual colonoscopies, when they weighed the medical benefits against potential risks, including radiation exposure.

CT scans under scrutiny

Medical imaging is only part of the radiation equation, contributing half of the total exposure, according to radiation experts. Background radiation and occupational exposure also are sources. But CT scans are under particular scrutiny because they are being used so frequently—roughly half of the medical imaging increase was linked to CT scans.

Also, CT scans can involve significantly more radiation than some other imaging tests. A CT scan of the abdomen involves a radiation dose about 50 times higher than an abdominal x-ray, according to Brenner.

For Liebross, the cost—$350 out of pocket—and related radiation exposure from her CT scans were a small price to pay for peace of mind. Her lungs looked great. Her heart was plaque-free. “I think the limited amount of radiation exposure was worth finding out the results,” she says.

Radiation exposure guides

So how much radiation exposure is worrisome? To date, researchers have extrapolated from other experiences with radiation, including the cancers that developed among atomic bomb survivors in Japan.

According to the Health Physics Society:

  • A lifetime radiation dose of 100 mSv increases cancer risk by roughly 1 percent. Thus, the average lifetime risk of developing cancer, 42 percent, would be increased to 43 percent.
  • As a rule, 100 mSv equals about 1,000 chest x-rays, 250 mammograms, 50 head CT scans, 13 abdominal or pelvic CT scans, or 10 cardiac nuclear imaging tests.
  • In short, someone who has battled cancer or heart disease and requires repeated CT scans has accumulated more lifetime radiation exposure than someone who only gets periodic mammograms and dental x-rays.

And radiation is only one of many factors that can potentially influence cancer’s growth, says Peter Shields, M.D., deputy director of Georgetown University’s Lombardi Comprehensive Cancer Center.

But patients should still take the initiative and ask their doctor about the need for imaging tests, experts say.

NOTE: Magnetic resonance imaging, MRI, also an expensive technique used with increasing frequency, does not expose patients to radiation.

Charlotte Huff is a Texas-based health and business writer.