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Am Fam Physician. 2010;82(11):1312-1314

Original Article: Cancer Risks Associated with CT Scanning [AFP Journal Club]

Issue Date: January 15, 2010

to the editor: I very much appreciated the AFP Journal Club on cancer risks associated with computed tomography (CT) in which the authors ably review an important study by Einstein and colleagues.1 Although the facts in the Journal Club review are accurate, the framing seems somewhat misleading and the tone unnecessarily alarmist (especially with regard to women and children).

The Journal Club authors make comparisons between radiographic tests, showing that, for example, a chest CT provides about 600 times as much radiation (approximately 6 mSv) as a chest radiograph. This is indeed concerning; however, readers may be interested to learn that the average person in the United States is exposed to about 3 mSv of “background” radiation annually (cosmic radiation from outer space and radiation naturally occurring from terrestrial sources).2 Given the Journal Club authors' particular concern for children, it is important to know that an average child in the United States who lives to 12 years of age has already sustained a cumulative background radiation dose equivalent to about six chest CTs.

Just as radiation dose is cumulative, so is cancer risk. Cancer develops through cumulative DNA mutations (naturally occurring or through radiation or other injury). As noted by a prominent cell biologist, if we live long enough, cancer is a statistical inevitability.3 Indeed, cancer is already the second leading cause of death in the United States.4 Thus, although it is certainly concerning that the lifetime risk of cancer from a single CT angiogram in a 20-year-old woman is about one in 143,1 we should keep in mind that the same 20-year-old woman already has a background lifetime risk of cancer of about one in three.5

In light of these considerations, the article reviewed for Journal Club1 is less frightening and scary than the Journal Club authors make it out to be. Make no mistake, ionizing radiation does increase the risk of cancer, and CT is not a benign diagnostic procedure; however, I think most family physicians have long appreciated the risks. I would be surprised if any family physicians are obtaining “a CT for every child because they have a bump on the head, or because the parent wants a test” as Dr. Darby-Stewart suggests. As with all diagnostic and therapeutic interventions, the risks and benefits of CT must be carefully considered. I am confident that, in considering the facts, family physicians can use radiographic tests responsibly, thoughtfully, with level heads, and when medically indicated in the care of their patients.

in reply: Dr. Lucan asserts that because we naturally receive background radiation from our environment, it is okay to get an additional two years' worth of radiation in a 10-minute chest computed tomography (CT) scan. I disagree with the argument that because a 12-year-old child has accumulated the equivalent of six chest CTs, it is acceptable to bestow two additional years of ionizing radiation to his or her young body.

Dr. Lucan's argument that the cancer risks are not as “frightening and scary” as we noted in our Journal Club review is not well-grounded. He rationalizes that because a 20-year-old woman already has a one in three lifetime risk of developing cancer, the one in 143 risk of cancer from one 64-slice chest CT is not “scary”; however, this is a one in 143 risk of premature cancer centered in the thorax (i.e., breast, lung, or thyroid).

Family physicians are in the business of preventing disease. Despite the fact that one in 2.9 Americans dies of cardiovascular disease, we do everything we can to prevent the premature development of this disease.1 Should we not take the same approach to prevent the premature development of cancer?

Dr. Lucan also assumes that many family physicians “have long appreciated” the radiation risks associated with diagnostic imaging studies. However, a recent survey demonstrated that 194 of 413 (47 percent) nonradiologist physicians in the Atlanta, Ga., area had no idea of the cancer risks associated with CT.2 The escalating number of CTs performed in the United States (in 2007, nearly 70 million CTs were performed3) sends a clear message that CT is overused. If our Journal Club review signaled a “clarion call” or struck a nerve with readers, I feel we did our job. We need to recognize that this wonderful imaging modality, like many of our therapies, is a double-edged sword. Because family physicians stand on the forefront of prevention, we need to be thoroughly aware of the risks associated with CT to best serve and protect our patients.

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This series is coordinated by Kenny Lin, MD, MPH, deputy editor.

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