The risk of potentially harmful effects from ionizing radiation is low at the radiation dose levels used in cardiac imaging exams; however, because the exact level of risk is unknown, people without symptoms of heart disease should think carefully about undergoing these exams, according to an advisory panel’s recommendations in the Feb. 2 online issue of Circulation.
A committee, convened by the American Heart Association (AHA)'s Council on Clinical Cardiology and Council on Cardiovascular Radiology and Intervention, wrote that cardiac scans that use ionizing radiation should, in all cases, be used judiciously, and are not recommended for people without chest pain or other symptoms who are at low risk for heart disease.
“There is a false sense of security among physicians that the radiation dose received by individual patients, and the potential health risks that may come with it, can be determined precisely,” said Thomas Gerber, MD, PhD, a cardiologist at Mayo Clinic campus in Jacksonville, Fla.
The uncertainty, and long-standing controversy, centers on how to connect the low doses of ionizing radiation received by patients from medical imaging procedures to the possibility of cancer development, according to Gerber.
The “controversy” has been further brought to light by a study in Tuesday’s Journal of the American Medical Association, in which study authors cautioned that cardiac CT angiography (CCTA) has the potential to expose patients to high doses of radiation, and tasked physicians and technologists with using methods to reduce radiation dose more frequently.
“We expect that the amount of radiation exposure attributable to CT imaging of the heart will rise rapidly as the technology improves and becomes more readily available,” Gerber said. “However, the benefit of performing these scans in patients without symptoms is still unclear, and patients should know that."
Yet, the authors wrote that the use of appropriate diagnostic imaging studies, such as CCTA, fluoroscopy and nuclear medicine studies, should not be avoided in patients with symptoms of heart disease just because of concerns regarding radiation dose. "If a person has symptoms, the benefit of using these tests to come up with a treatment plan outweighs the small potential risk,” Gerber noted.
The AHA asked the writing committee to explain to physicians how radiation dose to patients is determined, as a way of helping cardiologists understand and explain the risk and benefits of imaging procedures that use ionizing radiation.
The authors wrote that the most widely used measurement of the effective dose "isn't as precise as people would like to think." Because it does not take into account age, variations in human anatomy, or uncertainties as to the sensitivity of organs and tissues to radiation, "the effective dose applies generically to types of imaging studies but not to individual patients," Gerber said.
The committee also noted that the risk of dying from cancer related to ionizing radiation from a CCTA is less than the risk of drowning, or of a pedestrian dying from being hit by some form of transportation.
Additionally, the authors cited a hypothetical scenario where, if every person aged 50 to 55 in the U.S. (about 1.8 million people) were screened for heart disease with CCTA every five years until age 70, the estimated total increase in the number of fatal cancers over the entire 20 years might be about 43,000. Yet, if doctors could use that screening information to prevent only 10 percent of the unexpected deaths from heart disease, 35,000 fewer deaths would occur per year.
"The bottom line is that patients need thoughtful advice from their doctors as to what heart imaging test is right for them,” Gerber said. "Their doctors need to understand and be able to carefully weigh the risks and benefits of these tests in each patient's special situation.”