A common test to diagnose or stage patients with chest pain and breathing difficulty for heart disease is often done multiple times, exposing patients to potentially harmful, and perhaps unneeded doses of radiation, according to a report published Monday in the Journal of the American Medical Association.
The authors say that a single such myocardial perfusion imaging (MPI) exam has the highest radiation burden, "accounting for 22% of cumulative effective dose from medical sources."
But these tests are frequently administered without regard for the number of prior tests performed, the interval between tests, the nature of any abnormal findings and whether any were inconclusive, according to the researchers, led by Andrew Einstein, MD, and colleagues at Columbia University Medical Center in New York.
"Future efforts need to focus not just on individual test justification, but on optimizing and validating longitudinal imaging strategies to lower cumulative doses while ensuring performance of imaging needed for therapeutic decision making," the researchers wrote.
Also, current guidelines for administering MPI are detailed, but "do not yet simultaneously consider the appropriateness" of exams that don't involve radiation, such as stress echocardiography, stress magnetic resonance imaging and exercise electrocardiography.
The researchers studied a cohort of 1,097 patients undergoing MPI tests at Columbia during the first 100 days of 2006 to evaluate how many tests they received and how much radiation.
"More than 30% of patients received a cumulative estimated effective dose of more than 100 mSv, (millisievert) a level at which there is little controversy over the potential for increased cancer risks," they wrote.
The patients in the study underwent a median of 15 procedures involving radiation exposure, and of those four were high-dose procedures, equal to the amount of radiation one would be exposed to from the environment during one year.
Nearly 20% of the patients had at least three MPIs and 4.9% had at least five.
The volume of MPI testing increased from fewer than 3 million procedures in 1990 in the U.S., to 9.3 million in 2002, and "is now estimated to account for more than 10% of the entire cumulative effective dose to the U.S. population from all sources, excluding radiotherapy," they wrote.
For 39% of the patients who underwent more than one MPI, the dose was 121 mSv, "higher than that in the exposed (greater than or equal to mSv) cohort in the Life Span Study of Japanese atomic bomb survivors," they wrote.
The researchers do not suggest that the tests were inappropriate, and in fact emphasized that "the clear majority of MPI examinations were performed for reasons presently regarded as appropriate, and with the potential to effect therapeutic management."
Rather, they say, because the amount of radiation exposure is "a matter of concern," the tests should be viewed not in isolation "but rather within the clinical context where radiation risk for a specific patient is balanced against potential benefits."
Other studies have found similar amounts of radiation exposure for patients undertaking cumulative CT or MPI exams, they wrote.
"The findings of these studies, together with our findings, suggest that although most individuals receive little radiation from medical procedures, there exist certain groups of patients who receive high cumulative doses of radiation. Patients undergoing MPI, particularly those undergoing repeat MPI, are one such group. Efforts to reduce cumulative radiation dose should be especially targeted toward such groups," they wrote.
The authors also discovered a gender, racial, and economic disparity in who gets such tests. "Men, white, and uninsured patients had higher odds of undergoing multiple MPI studies and received more MPI examinations, fluoroscopic procedures and higher cumulative dose," they wrote. "Whether this disparity in radiation doses represents an advantage or disadvantage is dependent on whether increase in utilization results in improved cardiovascular outcomes, and requires further study." They wrote.
The report may be viewed here.