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Coronary CT scans may raise your cancer risk: experts warn widespread use could increose the number of excess radiation-induced cancers. Women are especially vulnerable.

Use of computed tomography (CT) to assess the amount of calcified plaque in the coronary arteries is accepted as an alternative to catheterization in patients at low-to-intermediate risk for coronary artery disease (CAD) who present with chest pain. It is also becoming an increasingly popular method for routine CAD screening in asymptomatic patients as part of a comprehensive risk assessment. But a study in the July 13 Archives of Internal Medicine concluded that widespread use of this technology could dramatically increase the number of radiation-induced cancer cases in the U.S., with women especially at risk.

How the study was performed

The authors estimated the radiation doses from various protocols utilized in published clinical studies of coronary CT angiography (CCTA) and applied these estimates to radiation risk models to obtain the excess lifetime risk of radiation-induced cancer. They concluded that if 50 million healthy Americans--the number proposed by Screening for Heart Attack Prevention and Education guidelines--undergo a single screening with a medium dose of radiation, an additional 5,600 cases of radiation-induced cancer would occur. Screening every tive years would increase the excess cancer risk by 62 per 100,000 women and 42 cases per 100,000 men.

Women and risk

In January 2009, Women's Heart Advisor ran a story on this subject before the risks of excess cancer were known. Cleveland Clinic cardiovascular imaging specialist Ronan Curtin, MD, expressed concern that CCTA could cause long-term increased risk of breast and lung cancer, because these organs readily absorb radiation. Rapid cell turnover increases the chance that developing cells will mutate, causing cancer.

Because such changes would produce slow-growing cancers, the lifetime risk decreases with age, Dr. Curtin said. A study reported in the July 18, 2007, Journal of the American Medical Association found the increased lifetime estimated risk of developing cancer following a CCTA study was i in 143 for a 20-year-old woman and i in 715 for a 60-year-old woman--a sufficient difference that "extra caution should be exercised before ordering this test for women in their 20s to 40s," he said.

More studies needed

Part of the problem may lie in the absence of a standardized screening protocol. In the Archives study, a 10-fold difference in the amount of radiation delivered during CCTA was seen, even when the tests were performed on identical machines in different hospitals. Establishing a safe dose of radiation for the test would minimize cancer risk. Additionally, further studies need to be done to confirm the benefits of CCTA. Until these issues are addressed, the potential cancer-causing risks of the technology should be balanced with its potential benefits.

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DR. CHO'S VIEW ...

It is crucial for patients to understand that radiation risk exists not only with coronary CT, but with other cardiac tests as well. Nuclear stress tests expose patients to high levels of radiation. Cardiac catheterization may also give patients a moderate radiation dose, depending on the length of the procedure. For younger patients, I typically tend to favor stress echocardiography, since the ultrasound-based technology emits no radiation.

For any test, it is important to weigh the risks and the benefits. If you are concerned about the radiation risk, talk to your doctor. At Cleveland Clinic, we use several sophisticated dose-limiting protocols for coronary CT that we helped to develop. For example, instead of leaving the X-ray tube on continuously while the scanner revolves around the patient, we can turn the X-ray tube on only during short intervals of the patient's heartbeat. This reduces X-ray exposure by 50 to 75 percent, to a level similar to that of cardiac catheterization.

LESLIE CHO, MD, Director of Preventive Cardiology and Rehabilitation at Cleveland Clinic, Heart Advisor Editor-in-Chief
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Title Annotation:WARNINGS; computed tomography
Author:Cho, Leslie
Publication:Heart Advisor
Geographic Code:1USA
Date:Oct 1, 2009
Words:612
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