Virtual Colonoscopy Effective for Colon Cancer Screening

May 30, 2001
News Office: Kevin Boyd (415) 502-6397

Many patients dread colon cancer screening because the diagnostic procedure, colonoscopy, is uncomfortable and invasive. A new study, however, shows that a faster, safer and potentially more pleasant technique works just as well. The so-called virtual colonoscopy uses a CT (computed tomography imaging) scan to search for pre-cancerous polyps. The new study compared the virtual technique to standard colonoscopy, which involves snaking a long tube-shaped camera through the length of the colon.

Dr. Judy Yee, UCSF assistant professor of radiology and chief of CT and gastrointestinal radiology at San Francisco Veterans Affairs Medical Center (SFVAMC), said, "Since this technique requires no anesthesia, has no risk of complications from perforation or bleeding and may be better tolerated by patients, we hope that it will increase the number of people willing to come in for screening." The vast majority of colon cancers are treatable if detected at an early stage, she added.

Although colon cancer is the No. 2 cancer killer in the United States, less than 40 percent of adults eligible for screening undergo the procedure, Yee said. The American Cancer Society recommends colon cancer screening for anyone age 50 or older and for younger people who have a family history of the disease.

Among the 300 patients in Yee's study, the largest series published so far, virtual colonoscopy identified 90 percent of the large polyps found using regular colonoscopy. Only polyps 10 millimeters in diameter or larger are considered clinically significant with a greater potential to develop into a cancer. Virtual colonoscopy identified every patient with clinically significant polyps, Yee said

Once a potentially problematic lesion is identified by virtual colonoscopy a patient must then undergo a standard colonoscopy. During this exam a biopsy may be performed to give a clearer picture of whether or not the polyps might be cancerous, Yee said. The study was published in the June 2001 issue of the journal Radiology.

In addition to its effectiveness at discovering colon cancer, virtual colonoscopy also can detect diseases and problems in other organs. The CT scan creates an image of the entire lower abdominal area, so radiologists can find problems such as kidney cancer, aneurysms in the aorta and even lung cancers near the bottom of the lungs.

Virtual colonoscopy also is faster for the patient than traditional screening. Whereas standard colonoscopy can take between 30 minutes to one hour, not including time required to recover from sedatives, the CT scan takes roughly a minute to perform, Yee said.

Once collected, the data is transmitted via fiber-optic cable to a workstation equipped with specialized analysis software, which can create three-dimensional images of the interior surface of the colon and highlight parts of the colon where a polyp is likely to exist. The radiologist can rotate the images, zoom in and out, and even create movie loops that look like a trip through the inside of the colon.

The time required for analysis is one of the drawbacks for virtual colonoscopy, Yee said. "Until we have more advanced software that decreases the analysis time from 30 minutes to about 10 minutes, it's unlikely that HMO's and other health care payers will be willing to add this as a covered expense," she said.

Yee currently is working with Duke University on a three-way comparison of virtual colonoscopy with barium enema (another popular screening technique) and traditional colonoscopy, funded by the National Institutes of Health.

Co-authors on the newly published study included: Dr. Geetanjali Akerkar, staff gastroenterologist at SFVAMC; Dr. Kenneth McQuaid, UCSF associate professor of gastroenterology and SFVAMC gastroenterologist; Dr. Raymond Hung, UCSF/SFVAMC radiology fellow; Dr. Andreas Steinauer-Gebauer, UCSF/SFVAMC radiology fellow; and Dr. Susan Wall, UCSF professor of radiology and SFVAMC radiologist.

The work was supported by grants from the UCSF Department of Radiology, as well as vendor grants, managed by the Northern California Institute for Research and Education (NCIRE). NCIRE is one of the fastest growing medical research groups in the nation. Founded in 1988, NCIRE now manages more than $30 million in funding from organizations such as the National Institutes of Health, National Aeronautics and Space Administration and National Science Foundation. Based at the San Francisco VA Medical Center, NCIRE is the largest of the 80 congressionally authorized VA research corporations.

The San Francisco Veterans Affairs Medical Center has been a primary affiliate of University of California, San Francisco since 1974. The UCSF School of Medicine and the SFVAMC collaborate to provide education and training programs for medical students and residents at SFVAMC. SFVAMC maintains full responsibility for patient care and facility management of the medical center. Physicians at SFVAMC are employed by the Department of Veterans Affairs and also hold UCSF faculty appointments.