"I think we have demonstrated that laxative-free CTC is a valid tool for detecting polyps that are clinically significant," said Doctor Judy Yee of University of California San Francisco.
Virtual colonoscopy uses a CT scanner to screen for cancers and polyps in the colon non-invasively. In standard optical colonoscopy (OC), a physician inserts a six-foot-long scope into the entire colon. Currently, both methods call for patients to take a bowel-cleansing laxative before the procedure.
With laxative-free CTC, explained Yee, patients do not have to go through bowel cleansing before the exam, but instead begin a low fibre diet two days before the test. They also ingest a tagging agent the day before the exam, which mixes with residual material in the colon and can then be identified and removed digitally when radiologists interpret the scans.
"The use of laxatives is often viewed as the worse aspect of having not only a virtual colonoscopy but an optical colonoscopy," said Yee. "I hope that this research will encourage patients who have delayed screening for colon cancer to be examined with this less invasive method."
The study of 605 patients, aged 50 to 85, assessed the accuracy of laxative-free CTC in detecting lesions 6 millimetres or larger in size compared with standard optical colonoscopy.
The authors found that laxative-free CTC exams detected clinically significant polyps 10 mm or larger with 91 per cent accuracy compared to OC exams, which were 95 per cent accurate. Statistically, there is no difference between these two numbers, said Yee.
Scan sensitivity using laxative-free CT colonography decreases with polyp size, as it does for regular CT colonography, she said. With polyps measuring 6 mm, sensitivity for CTC was 59 per cent, compared with standard colonoscopy at 76 per cent.
MEDICA.de; Source: NCIRE - The Veterans Health Research Institute