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Rapid Responses to:
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Electronic letters published:
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Computed Tomographic Colonography- Radiation Risk and Informed Consent
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Eric R Frizzell, M.D. Walter Reed Army Medical Center, Inku Hwang, M.D.
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eric.frizzell{at}na.amedd.army.mil Eric R Frizzell, et al.
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TO THE EDITOR: We read with interest the recent meta-analysis of computed tomographic colonography (CTC) by Mulhall and colleagues. Although we agree that this novel modality holds promise, the radiation risk from potential repeated exams has not yet been well addressed. Given that small (<5-8 mm) adenomas are common, and their risk of malignancy is low, guidelines have been proposed suggesting that 5-8 mm polyps on CTC be left in place with CTC surveillance in 1-3 year intervals to assess for stability of polyp size. (1) This poses a potential health risk, as a radiation dosage of 8 to 12 mSv, which is the estimated radiation exposure with a single CTC, has been reported to increase the risk of malignancies.(2-4) To date, there has been one publication estimating the life-time risk of malignancy from radiation exposure during CTC, as a single screening test or for surveillance with a risk of radiation related death of between 0.3% and 0.24% with a 3 or 5 year surveillance interval, respectively.(5) Given this potential risk, it may be important for physicians to accurately inform patients of the risk of ionizing radiation with CTC. While the risk of malignancy from a single CTC is likely low, the risk from repeated surveillance with CTC may not be acceptable for many patients. These risks may be further clarified with studies of the actual growth rate and neoplastic potential of small adenomas versus the actuarial cancer risk from ultra-low dose CTC .(3, 4) Alternatively, CTC may be envisioned as a preliminary screening tool to identify individuals with large polyps who should be referred for polyp removal and future surveillance colonoscopy. Before CTC is embraced as an accepted standard of care for colorectal cancer screening or surveillance we need to develop better guidelines on its usage, better define the risks from ionizing radiation, and adequately inform patients of the risks of ionizing radiation exposure, ideally through well designed clinical trials. Informed consent for patients undergoing elective CTC for screening, to include the potential risk of radiation related secondary malignancies should be considered. Eric Frizzell, M.D. Inku Hwang, M.D. Walter Reed Army Medical Center Washington, DC 20307-5001 Disclaimer: The opinions and assertions contained herein are the private views of the authors and are not be to be construed as reflecting the views of the Department of the Army or the Department of Defense 1. Pickhardt PJ, Choi JR, Hwang I, et al. Computed tomographic virtual colonoscopy to screen for colorectal neoplasia in asymptomatic adults. N Engl J Med. 2003;349(23):2191-200. 2. Brenner D, Elliston C, Hall E, Berdon W. Estimated risks of radiation- induced fatal cancer from pediatric CT. AJR Am J Roentgenol. 2001;176(2):289-96. 3. Macari M. Virtual colonoscopy: clinical results. Semin Ultrasound CT MR. 2001;22(5):432-42. 4. van Gelder RE, Venema HW, Florie J, et al. CT colonography: feasibility of substantial dose reduction--comparison of medium to very low doses in identical patients. Radiology. 2004;232(2):611-20. 5. Wise KN. Solid cancer risks from radiation exposure for the Australian population. Australas Phys Eng Sci Med. 2003;26(2):53-62. Conflict of Interest:None declared |
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