It has been estimated by experts that up to 2 percent of all cancer cases are caused by exposure to medical x-ray tests. Although it is believed that there is no completely safe level of exposure to x-rays, it is well known that exposure to increasing doses of x-rays, as well as undergoing repeated x-ray examinations, increases the risk of cancer formation.

The increasing use of CT scanners (which can expose patients to significant doses of radiation) to screen asymptomatic patients for coronary artery disease has been a source of growing concern among many cancer experts. While the detection of coronary artery calcifications and coronary artery narrowing (stenosis) on multi-detector CT scanners are powerful predictors of future cardiac disease events, it remains unclear, at this time, whether or not this approach to coronary artery disease screening offers any significant clinical benefits to otherwise asymptomatic patients.

A newly published clinical research study, which appears in the current issue of the Annals of Internal Medicine, further quantifies the potential cancer risk associated with the use CT scans to screen for coronary artery disease.

Because there are no nationally standardized protocols for CT scan cardiac screening examinations, the authors of this study considered several commonly used CT scan protocols, and then calculated the actual dose of radiation delivered to patients with each of these scan protocols. Using long-term data derived from Japanese atomic bomb survivors, the researchers then estimated the added cancer risk to patients receiving coronary artery screening CT scans.

One important (and concerning) finding from this study is that radiation doses delivered to patients vary by more than 10-fold among the different CT scan protocols in common use throughout the United States.

Based upon existing screening recommendations, the authors calculated the added cancer risk associated with adult patients undergoing coronary artery screening CT scans every 5 years between the ages of 45 and 75 years for men, and every 5 years between the ages of 55 and 75 years for women. Using the very conservative assumption that all patients are exposed to a dose of radiation equivalent to the average of all commonly used CT scan protocols, the authors calculated that the lifetime increased incidence of cancer was 4.2 new cases of cancer per 10,000 men, and 6.2 new cases of cancer per 10,000 women. Based upon the known effects of radiation to the organs contained in the chest area, approximately 71 percent of the cancer cases caused by CT scans of the heart would be in the form of lung cancer, while 20 percent of these "excess" cancers would be breast cancers induced in women. Another 12 percent of these radiation-induced cancers would be in the form of leukemia in men, while 4 percent of these otherwise preventable cancers would manifest as leukemia in women.

Unfortunately, there is currently no scientific consensus regarding the clinical benefit, if any, of using CT scanners to detect coronary artery disease in asymptomatic patients, as there is no high level clinical research data available to prove that this screening approach reduces cardiac disease events, or cardiac-associated deaths. Therefore, all that can be confidently said, at this time, about the routine use of CT scans to screen for coronary artery disease is that it is, undoubtedly, associated with a small but not insignificant risk of otherwise preventable cancers. Moreover, when you consider that the authors of this study used very conservative estimates regarding absorbed radiation doses in patients undergoing coronary artery screening, the actual cancer risk associated with many of cardiac screening CT scan protocols in current use is probably significantly higher than what this study predicts.

In my own case, I underwent two separate CT scans, to assess for both coronary artery calcifications and coronary artery narrowing (stenosis), as part of a "VIP Physical" in 2006. At the time, there was great enthusiasm for the routine use of CT scanners for this purpose. However, based upon the available data (including the data from this study), I have recently decided that I will not undergo any additional heart screening CT scans until and unless compelling clinical data comes along to suggest that the benefit from such scans outweighs their potential risks. If you have been considering undergoing a routine cardiac screening CT scan, my advice is to first discuss the data contained in this clinical study with your Internist or Cardiologist, and ask them to clarify both the potential risks and benefits, in your particular case, of undergoing a coronary artery screening CT scan.

Meanwhile more research is needed to clarify what, if any, health benefits can be reasonably claimed for routine coronary artery screening CT scans in asymptomatic patients. Finally, in view of the immense variation in radiation doses associated with the various CT scanning protocols in common use today, professional radiology societies and boards should quickly work to reach a consensus on standardizing these protocols in such a way that unnecessary radiation exposure is minimized.



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