AJR 2001; 177:717
© American Roentgen Ray Society
CT As a Cause of Cancer
What's Old Is New Again
Everett Marc Lautin
New York, NY 10021
The February 2001 issue had three articles on the radiation risks of CT [1,2,3]. They are interesting, well documented, and valuable. But are they new? In an American College of Radiology publication in 1996, Radiation Risk: A Primer [4], section author Joel Gray, then of the Mayo Clinic, informed thousands of radiologists of the risk of cancer death for those who undergo CT (12.5/10,000 population for each pass of the CT scan through the abdomen; this rate compares with 12.0 cancer deaths from 1 year of smoking/10,000 population). After reading Gray's section, I contributed a letter to the editor of Radiology [5] with the caveat that CT, with its relatively high effective radiation dose, should not replace a test with a much lower effective radiation dose if the alternative (excretory urography, in my example) works as well. This should, of course, be a general axiom. A second letter to the editor [6] and a response to it [7] followed mine.
Gray [4] did not confine his calculations to pediatric patients, but his results of more than 4 years ago are similar to the conclusions of Brenner et al. [1]. Gray also strongly advocated that the CT radiation dose be reduced in studies performed on children and small adults, noting that this reduction would have no major effect on diagnostic value. This conclusion was reached more than 4 years before Paterson et al. [2] and Donnelly et al. [3] came to the same, clearly correct, conclusion. None of the three articles in the February 2001 AJR references Gray, my letter [5], or either of the letters that followed mine [6, 7].
More important, none of the three articles [1,2,3] makes the crucial point that a way exists to reduce radiation exposure from CT far more than would be achieved by appropriately reducing exposure factors during a CT examination. It is the simple expedient of not performing CT unless it is indicated. Obvious? Yes. Yet, do we not perform countless unnecessary CT examinations? Are we coerced by clinicians or, worse yet, by economic exigencies? Unfortunately, the honest answer is probably yes. Do we proffer an alternative test that will give the answer with less risk? Is any additional test, CT or otherwise, really needed? So many CT examinations are performed out of the emergency department that it would almost make sense to replace its door with a CT gantry and the CT table with a conveyor belt. Are these examinations all indicated?
A new trend is developing for obtaining what I call "vanity CAT scans." These are self-paid "screening" CT scans of most of the body obtained for people who usually have no symptoms. As expected, they produce a very low yield of findings for disease—while still potentially increasing the risk for some cancers. This trend has even made it in the media and is summarized in a May 25, 2000, article from USA Today that is posted on their Web site [8]. Many such examinations are obtained using multibeam scanners that currently give an even higher radiation dose than helical or nonhelical CT [9]. Might this be justified for use on people (not yet patients) more than 50 or 60 years old, in whom the expected yield might be somewhat higher and the radiation risk somewhat lower? I don't know. Do you? Does anybody? Risk—reward ratio, high. Justification, none. A bad idea.
CT is an extremely valuable tool, and nobody should hesitate to undergo CT when it is indicated. The operative word is "indicated." When CT is performed, the radiation must be kept to the minimum required dose and reduced appropriately for children and small adults. CT scans should not be obtained for vanity or curiosity, as part of a shotgun approach by an insecure physician, or certainly not for economic reasons. As Osler [10] said, "Physician, first do no harm."
References
1 Brenner DJ, Elliston CD, Hall EJ, Berdon WE. Estimated risks of radiation-induced fatal cancer from pediatric CT. AJR 2001;176:289 -296[Abstract/FreeFullText]
2 Paterson A, Frush DP, Donnelly LF. Helical CT of the body: are settings adjusted for pediatric patients? AJR 2001;176:297 -301[Abstract/FreeFullText]
3 Donnelly LF, Emery KH, Brody AS, Laor T, et al. Minimizing radiation dose for pediatric body applications of single detector helical CT: strategies at a large children's hospital. AJR 2001;176:303 -306.[FreeFullText]
4 Gray JE. Safety (risk) of diagnostic radiology exposures. In: Janower ML, Linton OW, eds. Radiation risk: a primer. Reston, VA: American College of Radiology, 1996:15 -17
5 Lautin EM, Schoenfeld A, Choudhri A. Subservience of excretory urography to unenhanced CT in evaluating renal colic: A good idea? Benefits and consequences. (letter) Radiology 1998;209:286 -287[FreeFullText]
6 Roebuck DJ, Metreweli C. Radiation risk in CT for acute abdominal pain. (letter) Radiology 1998;209:287[Medline]
7 Baker SR. Radiation risk in CT for acute abdominal pain: Dr. Baker responds. (letter) Radiology 1998;209:287 -288[Medline]
8 Appleby J. Want a CAT can? Step right up. USA Today, May 25, 2000. Available at: www.usatoday. com/life/health/hcare/lhhca094.htm
9 McCollough CH, Zink FE. Performance evaluation of a multi-slice CT system. Med Phys 1999;26:2223 -2230[Medline]
10 Familiar Medical Quotations, Stauss MB, ed New York: Little, Brown, 1975:625