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A CT-scan-based form of virtual colonoscopy that does not requirelaxative preparation appears to be as effective as standardcolonoscopy in identifying the intestinal polyps most likely tobecome cancerous. In the May 15 issue of Annals of Internal Medicine, a Massachusetts General Hospital (MGH)-based research team reportsfinding that the new technique, which uses computer-aided systemsboth to virtually cleanse and to analyze the images acquired, wasable to identify more than 90 percent of the common polyps calledadenomas that were 10 mm or larger. "While we know that colon screening can save lives, not enoughpeople participate, in part because of the discomfort of therequired laxative preparation," says Michael Zalis, MD, director ofCT Colonography at MGH Imaging, who led the study. "In our study,the laxative-free form of CT colonography performed well enoughthat it might someday become an option for screening, which we hopewould increase patient participation." Optical colonoscopy, the most common form of screening for colon cancer , allows examination of the internal surface of the colon through afiberoptic tube with a light and camera at the end. In addition tobeing sedated for the examination, patients must ingest laxativepreparations - sometimes up to a gallon of liquid - the precedingday in order to completed clean out the colon, a processuniversally regarded as unpleasant. CT colonography, which producesimages via CT scanning and not direct visualization, has becomeavailable in recent years. But while it is as effective ascolonoscopy for detecting polyps, does not require sedation, andcan be used in some patients for whom colonoscopy is notappropriate, CT colonography still requires the laxativepreparation that many patients choose to avoid. Preparation for the procedure tested in the current study involvestwo days of a low-fiber diet and oral ingestion of small doses of acontrast agent to label fecal material in the colon. Softwareprograms developed by the MGH team subtract labeled feces from theCT images and analyze the images for the presence of lesions -primarily adenomas, the type of polyps most likely to develop into cancer . The investigators recruited patients scheduled for screeningcolonoscopy between June 2005 and October 2010 at the MGH, Brighamand Women's Hospital, North Shore Medical Center and the Veteran'sAdministration Medical Center at the University of California atSan Francisco; and 604 patients completed the full protocol. The laxative-free CT colonography procedures were done within the 5weeks before the scheduled optical colonoscopies.Gastroenterologists performing the colonoscopies were not informedof polyps identified in the first procedure until they hadcompleted the initial examination, allowing a second-passcolonoscopy to confirm and if necessary remove any missed polyps.CT colonography results were interpreted by three MGH radiologiststrained in the use of both the virtual cleansing and the lesiondetection systems but blinded to the results of the colonoscopiesand to the diagnosis of any removed tissues. Patients alsocompleted written surveys of their experiences with both proceduresand were asked which they preferred. Study results showed the effectiveness of computer-assisted,laxative-free CT colonography to be comparable to that of opticalcolonoscopy for detecting adenomas 10 mm or larger. While it didnot do as well finding smaller polyps, those lesions are lesslikely to show cellular changes associated with higher risk forcancer development. Among colonoscopy-confirmed lesions that showedsuch risk-associated changes, 85 percent were 10 mm or larger.Three cases of colon cancer were diagnosed among the study group,and all of those lesions were 10 mm or larger and were detected byboth screening methods. Participants completing the surveyindicated that laxative-free CT colonography is more comfortableand easier to prepare for, and it was the preferred screeningmethod for 62 percent of respondents. "Colon cancer is common, with more than 120,000 new cases andapproximately 50,000 deaths in the U.S. each year; and it islargely preventable through screening. So the most important thingis for all adults over 50 to be screened," Zalis stresses. "Afterthe question of access to care, the biggest public health issue isgetting people to participate in any type of colon screening. Whileoptical colonoscopy is a very effective test, not enough people arewilling or able to undertake it. Our results suggest that this morepatient-friendly form of screening is feasible and can perform wellenough to really help screen patients. "If these results hold up in larger trials, we would expect thisprocedure would first be offered to moderate-risk patients who areotherwise unable or unwilling to be screened," he adds. "If we canvalidate that this form of CT colonography performs reasonably wellfor screening and is easier for patients, it could have asignificant impact on reducing the incidence of colon cancer andrelated cancer deaths." An associate professor of Radiology atHarvard Medical School, Zalis notes that the radiation doseassociated with CT colonography is much lower than that ofdiagnostic CT scanning and would be considered safe for widespreadscreening. Additional References Citations. 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