Colorectal cancer screening using CT colonography: is radiation exposure an issue?

Analysis by A. Laghi

 

CT colonography is now considered as one of the colorectal cancer (CRC) screening tests for asymptomatic, average-risk individuals, as stated in the American Cancer Society (ACS) CRC screening guidelines released in March 2008 [ 1]. Unfortunately, the position of the ACS is not univocal, since other agencies, like the U.S. Preventive Services Task Force (USPSTF) [ 2], raised some concern, in particular because of the potential harms of the examination. Those concerns were the basis for the decision of Medicare to not provide reimbursement when this imaging modality is used for screening [ 3]. Among the potential harms mentioned by the opponents of CT colonography, risks related to radiation exposure represent a major problem.
To address this issue, A. Berrington de González and colleagues recently published a paper entitled “Radiation-related cancer risks from CT colonography screening: a risk-benefit analysis” [ 4]. The aim of their study was to assess the benefit-risk ratio between cancers prevented and those theoretically induced by a CRC screening program using CT colonography. The authors estimated radiation-related cancer risk by using updated risk projection and microsimulation models based on the National Research Council’s Biological Effects of Ionizing Radiation (BEIR) VII report [ 5]. Technical data for CT colonography were derived from protocol parameters used in the national CT colonography trial of the American College of Radiology Imaging Network (ACRIN) [ 6], where a total of 2296 examinations were performed in average-risk individuals. In particular, the estimated mean effective dose per CT colonography examination in that trial was 7 mSv in men and 8 mSv in women.

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