Friday, September 19, 2008

Virtual Colonoscopy

Ever had a colonoscopy? It’s not pleasant. A paper published this week in the New England Journal of Medicine (Volume 359, pages 1207—1217), titled “Accuracy of CT Colonography for Detection of Large Adenomas and Cancers” suggests an alternative to the traditional procedure for detecting colorectal cancer: a “virtual colonoscopy.” This X-ray technology uses Computed Tomography (CT), which Russ Hobbie and I discuss in Chapter 12 of the 4th edition of Intermediate Physics for Medicine and Biology. The NEJM article concludes that “in this study of asymptomatic adults, CT colonographic screening identified 90% of subjects with adenomas or cancers measuring 10 mm or more in diameter. These findings augment published data on the role of CT colonography in screening patients with an average risk of colorectal cancer.” To learn more about this study, see the Associated Press article by Mike Strobbe, and an article in US News and World Report.

Any X-ray procedure does have a risk associated with the radiation dose. A typical virtual colonsocopy has a dose of 5 to 10 mSv. By comparison, the yearly dose from the natural background radiation is about 3 mSv. (The sievert is a unit of dose equal to a Joule per kilogram, adjusted for its biological effectiveness. A mSv is one thousandth of a sievert.) See my December 7, 2007 entry in this blog, or Chapter 16 of the 4th edition of Intermediate Physics for Medicine and Biology, for more information about radiation safety and CT scans. Of course, any risk of radiation must be weighed against risks involved with traditional colonoscopy procedures.

Now for the bad news: You still need to
clean out your bowels before the procedure, regardless of which method you use: traditional or virtual.

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