Researchers have discovered that U.S. patients are more often exposed to excessive radiation during myocardial perfusion imaging — also known as a nuclear stress test — which is used to help diagnose and treat coronary artery disease.
According to a new study, radiation levels are higher during the scans in the U.S. than those in other countries, which is performed on millions of patients every year.
The researchers used data that was collected as part of the International Atomic Energy Agency (IAEA) Nuclear Cardiology Protocols Study. The data covers 308 nuclear laboratories in 65 countries; 50 were located in 22 U.S. states.
Data was collected between March and April 2013, and included 7,911 patients, of which 1,902 were Americans.
According to the study, patients in the United States will typically receive a 20 percent higher radiation dose than patients being tested outside the United States. “In part because American labs were less likely to adhere to recommended dosing guidelines,” the researchers said.
Author of the study, Dr. Andrew Einstein of Columbia University Medical Center, told Reuters in an email:
“When it is appropriately performed, the benefits of a nuclear heart scan far outweigh this radiation exposure. However, it is still incumbent upon doctors to minimize the amount of radiation that patients receive from such testing while simultaneously ensuring a good quality heart study.”
Coronary artery disease is caused by the buildup of cholesterol and other substances, affecting the flow of blood to the heart. It is still the most common type of heart disease in the United States.
Myocardial perfusion imaging involves using radioactive material and physical activity, which is a relatively noninvasive procedure allowing doctors to be able to measure heart function.
While the test is considered essential, researchers said the rise in the exposure to ionizing radiation raises concerns about potential radiation-related health effects.
To lower the risk of cancer linked to radiation exposure, the guidelines recommend exposure during myocardial perfusion tests be restricted to 9 millisieverts (mSv).
However, in the U.S. less than a quarter of patients, 24 percent, received lower than the recommended 9 mSv. Whereas patients outside of the U.S. received the recommended 9 mSv almost 43 percent of the time.
Patients in other countries were given radiation doses below 9.7 mSv about half the time. However, in the U.S. the dose was 11.6 mSv about half the time.
An editorial written by Dr. Rebecca Smith-Bindman, of the University of California, which was published in JAMA Internal Medicine with the study, suggests a more careful approach to the tests could reduce any unnecessary exposure to radiation. They also point out one method that could reduce radiation.
“Adopting a practice of stress-first imaging among patients undergoing MPI in the United States could result in a dramatic decrease in the average radiation dose without loss of clinical information,” Smith-Bindman wrote, noting that changes in dosages is not unheard of.
“The variation in radiation dose in the performance of MPI is consistent with what data have previously been reported for CT scans.”
Even though the risk of cancer linked to nuclear imaging is thought to be small, and is dwarfed by the risk of serious problems from heart disease, the results from these studies still highlight the need for doctors to do a better job of minimizing radiation exposure, Einstein told Reuters.
Radiation exposure will still cause cancer in a small, but real number of patients, Smith-Bindman noted in her editorial.
“The right imaging tests performed at the right time can lead to earlier and more accurate diagnoses, better treatment decisions, and improved patient outcomes, and advanced imaging has had a very positive impact on patient care,” she wrote.
Adding that: “Unnecessary and inappropriately performed tests harm patients by causing them discomfort and anxiety, by leading to a large number of irrelevant incidental findings, and by exposing them to ionizing radiation, which can have harmful effects on their health.”