July 10, 2010— -- Nearly one in 10 adults under age 65 in the United States gets radiation exposure from cardiac imaging over a given three-year period, researchers have found.
The researchers analyzed administrative claims from a major U.S. insurer for more than 90,000 nonelderly adults who underwent at least one cardiac imaging procedure. They found that 89 per 1,000 received an effective dose of ionizing radiation from the procedures greater than what these patients would normally receive through exposure to background radiation from natural sources.
Another 3.3 per 1,000 got cumulative annual doses above the upper limit for occupational exposure averaged over five years, Dr. Jersey Chen of Yale University in New Haven, Conn. and colleagues reported online in the Journal of the American College of Cardiology.
Extrapolating these results to the U.S. population in the same age range suggested that 636,000 people would be at risk from high cumulative effective doses of ionizing radiation from cardiac imaging, which the researchers called "considerable."
The public health and clinical implications aren't easy to determine since the cancer risk that comes with ionizing radiation is countered by the benefit of catching and treating potentially life-threatening heart problems, they noted.
But since cardiac imaging appeared to account for about 30 percent of the total annual exposure to radiation from medical testing overall, cardiologists bear particular responsibility for minimizing risk by selection of tests and optimal technical practices, Chen's group said.
An accompanying JAAC editorial agreed that these results should give cardiologists pause.
But Dr. Matthew J. Budoff and Dr. Mohit Gupta, both of Harbor UCLA Medical Center in Torrance, Calif., cautioned in the editorial "that the entire premise that radiation doses from medical testing causes cancers remains hypothetical."
Although ionizing radiation at high levels like atomic bomb exposure causes cancer and death, "the relationship between low-dose medical imaging and harm has never been established," they wrote in the editorial.
In their analysis, the researchers analyzed administrative claims from one of the largest private healthcare insurers, United Healthcare, for five major markets across the U.S. that had similar insurance characteristics.
This included all 952,420 adults ages 18 to 64 in Arizona, Dallas, Orlando, South Florida, and Wisconsin who were alive and continuously insured by the company from the beginning of 2005 to the end of 2007.
Overall, 9.5 percent of the insured adults ages 18 to 64 got at least one cardiac radiology procedure that exposed them to radiation over the three-year period for a population-based rate of rate of 60.3 per 1,000 enrollees each year.
Not surprisingly, older adults and men accounted for a larger proportion of the cardiac imaging procedures. The rate in men was 10.5 percent compared with women's 8.5 percent.
The proportion of individuals who had at least one procedure over the three-year period rose from 1.5 percent in those 18 to 34 years old to 20.9 percent in 55- to 64-year-olds.
Still, "our study demonstrates that there are sizable rates of radiation exposure for patients age 35 to 54 years, many of whom will likely live long enough for such long-term complications [as malignancy] to potentially develop," Chen's group wrote.
Alternative imaging modalities without ionizing radiation that provide similar clinical information for informed decision-making may be a better choice for these younger patients, the researchers suggested.
"For example, alternatives such as stress echocardiography or, in some cases, exercise testing alone without imaging could serve as alternatives to myocardial perfusion imaging scans," they wrote in JACC.