In recent years, radiologists have begun using CT colonography to screen for colon polyps. Colon polyps are benign growths that may develop into colon cancer if not removed. Many people resist screening because of the discomfort caused by conventional colonoscopy and other tests.
Although less invasive, until now the procedure primarily used 2D CT slices for polyp detection, which are likely less sensitive. With the addition of 3D "fly-through" images, virtual colonoscopy provides the complete picture, creating precise and detailed images of the interior of the colon in a minimally invasive manner.
VC is much less invasive than conventional colonoscopy, because it does not require an endoscope or tube in the colon, as used in conventional colonoscopy. With VC, there is minimal risk of low radiation exposure, bleeding or perforation of the colon. For people over age 50, the radiation they receive is within an acceptable limit. VC also requires no sedation, anaesthesia or hospital stay.
"The hope of this joint effort is to show that virtual colonoscopy can be used as a stand-alone screening exam on patients who have significant polyps", stated Dr. Perry J. Pickhardt, lead author and primary investigator of the virtual colonoscopy study conducted at NNMC. Dr. Pickhardt, who currently is an associate professor of radiology at University of Wisconsin Medical School in Madison, presented his findings on December 1 in Chicago at the Radiological Society of North America meeting.
For this study, Dr. Pickhardt, Dr. Choi and colleagues performed both conventional and virtual colonoscopy on 1233 asymptomatic adults, 97,4 percent of whom were at average risk of having colonic polyps. Overall, virtual colonoscopy detected more than 90 percent of significant polyps. For example, virtual colonoscopy detected 92,6 percent of polyps 8 mm and greater, whereas conventional colonoscopy detected 89,5 percent of such polyps. Two malignant polyps were present, and virtual colonoscopy detected both of them, while conventional colonoscopy missed one.
Previously conducted VC studies looked at people who were at high risk for colon cancer. The prevalence of finding an abnormality like a cancer is much higher in that type of patient population. VC proved to be equal or superior to regular colonoscopy, according to the findings. Most polyps that are missed by virtual colonoscopy are small, i.e. 5 mm or less, and are of little or no clinical importance, according to Dr. Pickhardt.
Virtual colonoscopy is able to identify occasional polyps that are located behind folds in the colon lining and may be missed by conventional colonoscopy."Virtual colonoscopy also sees beyond the inner lining of the colon to the muscular layer and the colon's outer surface and can be used to check for evidence of enlarged lymph nodes around the colon, which may indicate advanced, more invasive forms of cancer", Dr. Choi explained.
The joint study was also conducted at Walter Reed Army Medical Center in Washington, D.C., and the Naval Medical Center, San Diego. "The goal of screening with virtual colonoscopy is to increase the number of patients that would participate", stated co-author Lieutenant Colonel J. Richard Choi, Sc.D., M.D., principal investigator of the Virtual Colonoscopy Screening Project at Walter Reed. "Even though colorectal cancer is the second leading cause of cancer death and is almost always preventable, less than half of eligible patients undergo any form of screening."
The VC pilot-study centered out of NNMC will, in the future, enable the hospital to apply the new technology to active-duty members, retirees and TRICARE beneficiaries in a less invasive and equally accurate way when screening for colon cancer. It will have a profound impact on Naval Medicine and the quality of care that NNMC practices.
Plans are currently in progress to construct a Comprehensive Colon Cancer Center at the hospital beginning in 2004. Once the construction of the centre is complete, NNMC will shift to VC as the primary diagnostic tool and standard of care for colon cancer screening. The new Comprehensive Colon Cancer Center will allow NNMC to screen 15.000 patients a year for colon cancer compared to the current 2500. According to Dr. Choi, as a result of this study, Walter Reed is now already offering virtual colonoscopy as an alternative to conventional colonoscopy screening.