Radiation dose fears colorcoronary CTA guidelines

April 1, 2009

Citing uncertainties about a linkbetween ionizing radiation and cancer,an American Heart Association expertpanel is advising cardiac imagers to usecoronary multislice CT angiographyonly when its clinical benefits areclearly established.

Citing uncertainties about a link between ionizing radiation and cancer, an American Heart Association expert panel is advising cardiac imagers to use coronary multislice CT angiography only when its clinical benefits are clearly established.

Recommendations from a 14-member AHA science advisory panel were published online Feb. 2 in the journal Circulation. Commissioned in 2007 by the AHA's then-president Dr. Daniel Jones, the report was designed to establish a conceptual framework for weighing the risks and benefits of radiation exposure to patients from coronary CTA.

Cardiologists, radiologists, medical physicists, and nuclear physicians in the group found little firm footing among the 65 years of research attempting to measure the relationship between radiation exposure and cancer risk. They decided against adopting the conservative linear no-threshold hypothesis to guide their recommendations. This holds that no amount of radiation exposure, however small, is considered safe, according to Dr. Thomas Gerber, chair of the advisory group's writing committee.

Yet panel members found too many uncertainties, in research that began with studies of Hiroshima and Nagasaki atomic bomb blast survivors, to say that even a small radiation dose does not involve risk.

The report helps clinicians place the cancer risk from MSCT into context, said panel member Cynthia McCollough, Ph.D. The panel reported that the average lifetime risk of developing a malignancy from all causes is 41% and of death from that malignancy is 21%. The typical 10-mSv coronary CT angiogram induces about a 0.05% additional lifetime risk of death from a malignancy.

“You shouldn't look at this radiation as measurably changing the risk. It is in the background noise,” McCollough said. “These numbers are not anything to be afraid of. But you can't say there is no potential effect.”

That view is reflected in recommendations that urge clinicians to consider using echocardiography and other radiation-free imaging modalities. The panel recommended against coronary CTA for asymptomatic patients and cautioned practitioners to identify clear clinical benefits for coronary CTA before applying it to symptomatic patients. Clinicians were advised to make every effort to reduce patient dose while balancing the need for optimal image quality.

The recommendations were published two days before the first-ever dose survey for 64-slice coronary CTA appeared in the Journal of the American Medical Association. That multicenter study determined that the median effective dose of radiation was 12 mSv and fulfilled the AHA panel's final recommendation, Gerber said.

“We ask the imaging community to participate in the voluntary determination of diagnostic references for radiation dose from cardiac radiographic procedures,” he said. “That is precisely what the JAMA paper does.”