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According to a new study in The New England Journal of Medicine, at least four million Americans under the age of sixty-five are exposed to high doses of radiation annually from medical imaging tests; more than 400,000 of these patients receive very high doses, more than the maximum annual exposure permitted for staff at nuclear power plants or anyone else who works with radioactive material. The use of imaging tests has risen dramatically over the past two decades. Many researchers attribute this increase to more physicians buying CT and PET scanners to use in their offices. In 2007, the Department of Health and Human Services estimated that the number of CT scans given to Medicare patients almost quadrupled from 1995 to 2005, while the number of PET scans rose even faster. The use of scans has even increased from 2005 to 2007.

The paper was based on a survey from 2005 to 2007 that covered almost one million patients insured by UnitedHealthcare; it did not, however, estimate the number of cancer cases the radiation may cause over the next several decades. One doctor who has extensively studied the use of medical imaging believes it will probably result in tens of thousands of additional cancers. Although each patient is only at a minor risk for developing cancer from the test, because tests are now conducted on so many patients, the cumulative risk is significant. By looking at the study, researchers have calculated that the amount of radiation Americans receive averages about three millisieverts each year from all sources. The study found, however, that in at least one of the three years, 1.9 percent of the UnitedHealthcare patients received at least seven times the average exposure, or 20 millisieverts of radiation. Of that group, about ten percent, or 0.2 percent of all patients, received at least fifty millisieverts, which is more than the annual maximum limit that nuclear regulators permit; these figures suggest that about four million Americans each year receive cumulative doses exceeding twenty millsieverts.

The radioactive tests are given for hundreds of different reasons but have become particularly common in cardiology, where doctors use them to check for the buildup of plaque in the arteries and the heart’s ability to pump blood. Some cardiologists are now encouraging patients to have routine heart scans even if they are having no clinical symptoms of heart problems, such as shortness of breath or chest pains. Unfortunately, however, the study did not show what percentage of these test are medically necessary. Though physicians are allowed to profit from the use of scan machines, researchers believe this is only part of the reason the number of tests has risen. Culture is another cause because doctors use imaging as opposed to examination. One researcher suggests patients ask if scans are really necessary because in many cases it has been proven that scans are not better than examinations.

In an editorial accompanying the paper, the director of prevention and epidemiology at the National Heart, Lung and Blood Institute called for large clinical trials that would determine whether the potentially hazardous scans improve care and lead to better outcomes for patients. Until then, he asks that patients and physicians discuss the risks of the tests and keep a close eye on the overall radiation dose the patient is receiving.

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