Cancer Rrisks From CT Scans: Now We Have Data, What Next? Radiology

Brenner DJ, Hall EJ. Cancer risks from CT scans: now we have data, what next? Radiology. 2012 Nov;265(2):330-1. doi: 10.1148/radiol.12121248. Epub 2012 Aug 20. PubMed PMID: 22915598.

It has been more than a decade since two articles were published that drew the attention of the wider community to the radiation exposures associated with pediatric computed tomography (CT) (1,2). One of the articles pointed out that most pediatric CT scans were being performed with adult-based settings, resulting in a higher radiation dose than was necessary in children who underwent CT scans (2). The other article (1) provided the first quantitative estimates of radiation risks associated with pediatric CT. The following day, the story hit the front page of USA Today, and the world of CT changed dramatically.

CT is a remarkable modality. It enables better surgery, better diagnosis and treatment of cancer, better treatment after injury, better treatment of stroke, and better treatment of cardiac conditions (3). Nonetheless, the suggestion that there might be some potential downside in terms of cancer risks has been vigorously challenged by many in the field (4–7). For example, a recent position paper from the American Association of Physicists in Medicine (5) states the following: “Risks of medical imaging at effective doses below 50 mSv for single procedures or 100 mSv for multiple procedures over short time periods are too low to be detectable and may be non-existent.”

The original risk estimates for pediatric CT (1) were derived from studies of exposed Japanese atomic bomb survivors (8). Clearly, there are many differences between a CT scan and an atomic bomb exposure; however, about 30 000 atomic bomb survivors who were located several miles from the bomb epicenter did indeed receive organ doses comparable with those from a few CT scans and did show a significant increase in cancer risk (9). Of course, CT scans are typically focused on a particular part of the body, whereas atomic bomb exposure was to the whole body. As far as possible, these differences were taken into account when estimating CT scan risks; however, the prediction that there is a small but real cancer risk associated with radiation exposure from CT did not convince everyone.

Now the first results of the first of several ongoing epidemiologic studies of pediatric CT recently have been published by Pearce et al (10). The authors identified 180 000 patients who had undergone about 280 000 CT scans in the United Kingdom between 1985 and 2002 when they were younger than 22 years of age. First, they estimated individual brain and bone marrow doses for every patient. Next, they ascertained the subsequent cancer history of these 180 000 patients until 2008 by using the UK National Health Service Registry—a study that can be done in the United Kingdom and in various other countries but that would be extraordinarily difficult to do in the United States! The authors restricted their initial study to leukemia and brain tumors because these are the cancers that might be expected to appear first in irradiated children (11,12), and as best as they could, they eliminated patients who might have had cancer at the time of CT.

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