JAMA: Cardiac CTA radiation exposure is nonnegligible

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Industry comments on study results

The radiation dose from coronary computed tomography angiography (coronary CTA) carries a “nonnegligible” cancer risk that varies widely with age, gender and scan protocol, researchers said in a study just published in the Journal of the American Medical Association.

Lifetime cancer risk from a standard cardiac scan was 4.8-fold higher among women than men at age 20, and 2.4-fold higher for women than men at age 80, according to the findings of Andrew J. Einstein, MD, PhD, of Columbia University Medical Center and his colleagues.

They found that risk decreased with age and was lower for men than for women at every age, to a degree that the risk was the same for a 20-year-old man and 70-year-old woman. The other major contributor was the "strikingly" higher radio-sensitivity seen for women, the researchers said. For the same 100 mSv dose of radiation to the lung at age 20, the attributable lung cancer risk was 346 cases per 100,000 for women but only 149 per 100,000 for men, according to the National Academies report.

The researchers concluded that their risk estimates could be used to assess the risk-benefit tradeoff for coronary CTA for patients, although the estimates were extrapolated without epidemiological data from patients actually undergoing scans.

The researchers, however, focused on the hypothetical, says Sam Wann, MD, a cardiologist at the Wisconsin Heart Institute. The researchers essentially recommended that coronary CTA not be performed on young women because of the increased radio-sensitivity of breast and lung tissue which leads to a higher risk of cancer in those tissues especially. However, this is a patient group that has a very low incidence of coronary artery disease and therefore has little reason to undergo coronary CTA.

“Everything in medicine has a greater or lesser risk and we should always pay attention to using our resources wisely,” says Wann. “It would be unfortunate if one were to become hysterical about it and over-interpret. I wouldn’t want my patients to be scared to death of radiation.” A big problem, he says, is that the latest technology allows for spectacular images so “it’s very tempting to take a bunchy of pictures and forget that each picture has a cost to it.” Wann uses Step & Shoot cardiac technology from Philips Medical Systems.

Manufacturers have been aware of radiation exposure concerns since the days of Marie Curie, Wann says. “Technological advances have reduced radiation exposure, so it’s very easy to be enthused about the new machines.”

Siemens Medical Solutions has a multicenter, multicountry trial in the works to look at radiation exposure and how physicians use imaging technology differently in different countries, according to Praveen Nadkarni, clinical business manager of the CT division. Much has been made of the greater focus on radiation exposure in Europe, for example. Germany has federal guidelines for radiation exposure and tracks lifetime exposure.

This study, Nadkarni points out, is based on hypothetical calculations, not actual data from patients who have undergone coronary CT imaging.

“Awareness around dose is a very positive thing,” says Gene Saragnese, vice president and general manager of GE Healthcare’s global CT business. Of the focus on exposure in Europe, “I’m starting to see more and more of that bleed over to the United States,” he says. The JAMA study will help accelerate an awareness of radiation exposure and therefore drive down dose, he says.

“Radiation dose is not trivial,” says Rich Mather, PhD, senior manager of clinical science for Toshiba America Medical Systems. “But that said, [coronary CTA] is an incredibly valuable exam and, done in the right patients, can do a lot to save lives and reduce radiation exposure in the long term.”

Mather says he has noticed an increase in awareness of radiation exposure in the past six to 12 months. “There has been more discussion and awareness especially within the cardiology community but the medical community as a whole. We see that as a good thing.”