Computed Tomography: Unquestionable Value, Unappreciated Risks

Computed tomography (CT) is one of the most useful diagnostic imaging tools available today. CT is considered the first-choice modality for a wide variety of indications, and there is little doubt that it has saved and improved many lives. But there is a price that must be paid for the considerable diagnostic information that it provides: CT delivers a higher radiation dose than many other common x-ray studies, thereby increasing the risk of inducing cancer from x-ray exposure.

Most CT exams use a high x-ray dose compared to other common x-ray studies. A typical CT exam delivers a radiation dose that is 100 to 400 times that of a single chest x-ray, which is one of the lowest-dose radiographic exams. Rigorous estimates of the risk associated with x-rays have been made; the most recent was published by a National Academy of Sciences committee to advise the U.S. government—the Committee on the Biological Effects of Ionizing Radiation. The report, known as BEIR VII (BEIR 2005), found that a typical CT exam incurs a risk of about 1 in 1,000 for causing cancer, with a mortality rate of about 50%. The risk is significantly higher for pediatric patients. (These CT-related cancers are in addition to those that occur for other reasons.) The BEIR VII estimate is similar to other estimates made by the International Commission on Radiological Protection (ICRP 2004), the...