Large Trial Shows Comparable Accuracy for Virtual Colonoscopy and Standard Colonoscopy
The Bottom Line
Results from a large multicenter trial show that (computerized tomographic (CT) colonography, also known as virtual colonoscopy, is comparable to standard colonoscopy in its ability to accurately detect colorectal cancer and precancerous colorectal polyps.
The Whole Story
Colorectal cancer is the third most frequently diagnosed cancer and the second leading cause of cancer death among men and women in the United States. Although screening guidelines vary, many doctors recommend that adults aged 50 years or older who are at normal risk of colorectal cancer receive a colonoscopy every 10 years. Most colorectal cancers arise from polyps (benign growths that may become cancerous over time), and detecting and removing polyps reduces the risk of colorectal cancer. Nonetheless, despite the known benefits of colorectal cancer screening, the majority of Americans age 50 and older are not being screened.
During colonoscopy, a long, flexible tube with a camera is used to view the lining of the colon and rectum. Most people are sedated during this procedure. In CT colonography, however, virtual reality technology is used to produce three-dimensional images of the colon and rectum, and sedation is often not required. Although bowel preparation for both CT colonography and standard colonoscopy involves drinking a solution to clear and cleanse the colon, the CT colonography procedure itself is minimally invasive, with no need for sedation or anesthesia. Other potential advantages to both patients and physicians have been identified, such as rapid visualization of the entire colon, low risk of complications related to the procedure, and lower cost than standard colonoscopy.
Previous single-institution studies had indicated that CT colonography was accurate and cost-effective, but it was important to confirm these findings in a multi-institution study that involved a larger number of radiologists. Therefore, the National Cancer Institute (NCI), part of the National Institutes of Health (NIH), sponsored the American College of Radiology Imaging Network (ACRIN) National CT Colonography Trial, which enrolled more than 2,600 participants at 15 institutions nationwide. This trial is the largest multi-institution study to date to compare the accuracy of state-of-the-art CT colonography with standard colonoscopy.
Participants in the ACRIN trial had to be at least 50 years of age, already scheduled for a screening colonoscopy, and not have had a colonoscopy in the previous five years. They were recruited for the trial with the assistance of gastroenterologists at each participating institution. Each participant had CT colonography followed by standard colonoscopy, with 99 percent of them receiving both exams on the same day.
Because the participants received both examinations, the findings from CT colonography could be directly compared with those from standard colonoscopy. The results showed that CT colonography was highly accurate for the detection of intermediate- and large-size polyps. CT colonography detected 90 percent of the cancers and precancerous polyps that were 1 centimeter or larger in size. Even polyps as small as 5 millimeters could be detected by CT colonography with a high degree of accuracy.
Despite its accuracy and possible benefits, CT colonography has several potential downsides. One is that any polyps detected during the procedure must be removed during a separate, standard colonoscopy procedure, whereas, with standard colonoscopy, polyps can be removed during the same examination. Another is CT colongraphy's ability to produce images of organs outside of the colon, which could lead to findings that need further evaluation. Such "extra-colonic" findings could potentially result in the detection of asymptomatic early cancers or other serious problems, but they could also lead to unnecessary tests and surgery. Yet another concern relates to the radiation exposure from repeated CT scans. Additional studies will be needed to determine the relative importance of these issues in relation to the lower cost and improved convenience of virtual colonoscopy. At present, most insurance companies do not reimburse the costs of CT colonography.
More summaries of selected scientific advances from NCI-supported research are available at http://www.cancer.gov/aboutnci/servingpeople/advances.