A new study says that the average American is exposed to six times more radiation from medical tests than in the early 1980s, prompting warnings that physicians may be upping patients' cancer risk by giving them unnecessary exams. 

A study by The National Council of Radiation Protection and Measurements (NCRP) shows that the average American's overall radiation exposure jumped from 3.6 millisieverts (mSv) to 6.2 mSv per year -- almost entirely a result of radiation-based medical tests. These tests, once responsible for only 15 percent of Americans' exposure to radiation, now account for nearly 50 percent. In contrast, there was almost no change in so-called background radiation, which naturally emanates from soil, rocks and other environmental substances.

The increase in medical radiation exposure (from 0.53 mSv to 3.0 mSv) stemmed primarily from a rise in the use of computer tomography (CT) scans (which use x-rays to create cross sectional images of inside the body to spot tumors, clogged arteries, among other things), and nuclear imaging tests, which involve injecting radioactive chemicals into the bloodstream that can be picked up by special instruments and used to create images of the body's inner structures.

The advantage of these tests is that they are generally better for diagnosing conditions than older technologies [such as standard x-rays, which expose patients to much less radiation], says Arl Van Moore, president of the American College of Radiology. "But we are concerned about the overuse of radiation through self-referral," or doctors ordering exams that can be done in their own offices for their own financial benefit, he says.

Need medical tests and worried about radiation exposure? Walter Huda, a medical physicist at the Medical University of South Carolina in Charleston, advises that you press your doc on why he or she has ordered the exams – and ask whether the clinic is certified by the American College of Radiology to perform the tests.

One tidbit of good news from the report, says physicist David Schauer, NCRP's executive director: occupational exposure has been sliced in half during the same period. The major reason: employers have taken steps to protect them, such as installing lead-coated pipes in nuclear plants to prevent the escape of harmful radiation.