The new england journal of medicine n engl j med 357;22 www.nejm.org november 29, 2007 2277 review article current concepts Computed Tomography — An Increasing Source of Radiation Exposure David J. Brenner, Ph.D., D.Sc., and Eric J. Hall, D.Phil., D.Sc. From the Center for Radiological Re- search, Columbia University Medical Cen- ter, New York. Address reprint requests to Dr. Brenner at the Center for Radiologi- cal Research, Columbia University Medical Center, 630 W. 168th St., New York, NY 10032, or at djb3@columbia.edu. N Engl J Med 2007;357:2277-84. Copyright © 2007 Massachusetts Medical Society. T he advent of computed tomography (ct) has revolutionized di- agnostic radiology. Since the inception of CT in the 1970s, its use has increased rapidly. It is estimated that more than 62 million CT scans per year are cur- rently obtained in the United States, including at least 4 million for children. 1 By its nature, CT involves larger radiation doses than the more common, conven- tional x-ray imaging procedures (Table 1). We briefly review the nature of CT scanning and its main clinical applications, both in symptomatic patients and, in a more recent development, in the screening of asymptomatic patients. We focus on the increasing number of CT scans being obtained, the associated radiation doses, and the consequent cancer risks in adults and particularly in children. Al- though the risks for any one person are not large, the increasing exposure to ra- diation in the population may be a public health issue in the future. CT and Its Use The basic principles of axial and helical (also known as spiral) CT scanning are illustrated in Figure 1. CT has transformed much of medical imaging by providing three-dimensional views of the organ or body region of interest. The use of CT has increased rapidly, both in the United States and elsewhere, notably in Japan; according to a survey conducted in 1996, 2 the number of CT scanners per 1 million population was 26 in the United States and 64 in Japan. It is estimated that more than 62 million CT scans are currently obtained each year in the United States, as compared with about 3 million in 1980 (Fig. 2). 3 This sharp increase has been driven largely by advances in CT technology that make it ex- tremely user-friendly, for both the patient and the physician. Common Types of CT Scans CT use can be categorized according to the population of patients (adult or pediat- ric) and the purpose of imaging (diagnosis in symptomatic patients or screening of asymptomatic patients). CT-based diagnosis in adults is the largest of these catego- ries. (About half of diagnostic CT examinations in adults are scans of the body, and about one third are scans of the head, with about 75% obtained in a hospital setting and 25% in a single-specialty practice setting. 1 ) The largest increases in CT use, however, have been in the categories of pediatric diagnosis 4,5 and adult screening, 6-13 and these trends can be expected to continue for the next few years. The growth of CT use in children has been driven primarily by the decrease in the time needed to perform a scan — now less than 1 second — largely eliminat- ing the need for anesthesia to prevent the child from moving during image ac- Copyright © 2007 Massachusetts Medical Society. All rights reserved. Downloaded from www.nejm.org by JOHN YANOS MD on June 11, 2008 .