JACC Feature: MPI studies responsible for 74% of cumulative rad dose

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SPECT myocardial perfusion imaging with technetium-99m (Tc99m) shows normal findings. Image Source: Daniel S. Berman, MD, Cedars-Sinai Heart Institute

Cardiac imaging procedures represent an important source of ionizing radiation in the U.S., and the distribution of cumulative effective doses can lead to sizable radiation exposure for many individuals, according to a study published online July 7 in the Journal of the American College of Cardiology. Better strategies to minimize the radiation exposure from cardiac imaging procedures should be encouraged, said the study's lead author Jersey Chen, MD, in an interview.

Cardiac imaging procedures frequently expose patients to ionizing radiation, but their contribution to effective doses of radiation in the general population is unknown. “The main significance of the study is to bring to the attention of people who perform or refer patients for cardiac testing how much radiation the patients are getting,” said Chen, of Yale University School of Medicine in New Haven, Conn.

The authors used administrative claims to identify cardiac imaging procedures performed from 2005 to 2007 in 952,420 nonelderly patients aged 18 to 64 years with healthcare benefits administered by United Healthcare (UHC) in five U.S. healthcare markets: Arizona, Dallas, Orlando, Florida and Wisconsin.

Chen and colleagues estimated three-year cumulative effective doses of radiation in millisieverts (mSv) from these procedures. The researchers found that among 90,121 patients (9.5 percent) undergoing at least one cardiac imaging procedure, the mean cumulative effective dose over the three years was 23.1 mSv, whereas the median dose was 15.6 mSv. “If the physician knows these numbers he or she can calculate the risk and advantages for the patient or maybe look for alternatives that don’t use radiation,” said Chen.

“With approximately 191 million adults age 18 to 64 years in the U.S., annual effective doses of greater than 20 mSv per year from cardiac imaging procedures would occur in approximately 636,000 Americans if cardiac testing patterns were similar to those in our UHC population,” estimated Chen.

The researchers found that myocardial perfusion imaging (MPI) scans with planar imaging, SPECT or PET imaging contributed most to the radiation exposure among cardiac imaging procedures (74.2 percent), followed by diagnostic cardiac catheterization and/or percutaneous coronary intervention (21.4 percent).

The question of risks versus benefits should always be considered before cardiac imaging, said Chen. National Academies’ Seventh Biologic Effects of Ionizing Radiation report, estimates that a 100 mSv radiation dose would lead to one additional cancer per 100 individuals over a lifetime. Therefore, there is a risk for lifetime cancer for about 10 percent of the population who get a cardiac imaging dose of 23 mSv, said Chen. But since cardiovascular disease is the number one killer in America, in patients who have a high probability of having cardiac disease the benefits of imaging outweigh the risks, he added.

“Young patients would have a higher risk of cancer in their lifetime than older patients as it takes a while for the cancer to develop. With younger patients, you have to think of alternatives to MPI studies such as stress echo and stress MRI and exercise treadmill tests that would give similar data. Another option is low dose cardiac imaging,” Chen suggested.

The researchers also found that overall, 47.8 percent of cardiac imaging procedures were performed in physician offices, with the remainder divided between hospital inpatients (26.4 percent) and non-hospitalized patients who underwent imaging in hospital facilities (25.5 percent).

The majority of MPI and cardiac CT studies were performed in physician offices (74.8 percent and 76.5 percent, respectively). This is likely because doctors have easy access to MPI studies, according to Chen.

“This study defines where we are in terms of radiation dose in cardiac imaging and raises the awareness among physicians and patients,” summarized Chen.