Practice Issues Dominate Ongoing Virtual Colonoscopy Discussion

C. Daniel Johnson, M.D. Mayo Clinic, Scottsdale, Ariz.

Judy Yee, M.D. University of California, San Francisco

Publication of the final results of the National CT Colonography (CTC) Trial in The New England Journal of Medicine (NEJM) in September marked a turning point in the development of CTC. With its accuracy established, virtual colonoscopy is entering an era in which practice issues are paramount—topics like training and accreditation, reimbursement, management of extra-colonic findings and coordination with other specialties are now moving to the fore.

Coordinated by the American College of Radiology Imaging Network (ACRIN), the large, multicenter trial showed that CTC found 90 percent of the large polyps—10 mm and larger—found by traditional colonoscopy. While specificity was somewhat lower, at 86 percent, the findings were positive enough to trigger a change in national guidelines. In March 2008, on the basis of preliminary results presented at the ACRIN fall meeting in 2007, the American Cancer Society modified its colorectal cancer screening guidelines to include the option of CTC at five-year intervals.

"I think the clinical validation of CTC is now complete," said principal investigator C. Daniel Johnson, M.D., of the Mayo Clinic in Scottsdale, Ariz. Not only does CTC get good marks for performance, he said, the procedure is also likely to rate high on patient acceptance because it does not require sedation or taking a day off from work. He added that CTC is safer than colonoscopy, with lower risk of perforation. While costs vary substantially, he said, CTC "should be about half of the cost of colonoscopy," when costs are added up for the entire colonoscopy procedure, including room charges, anesthesiology, biopsy and pathology.

Training, Reimbursement Issues Arise

With increasing acceptance of CTC, one of the most immediate and important issues for practicing radiologists is training.

"It does require a special skill set," said Dr. Johnson. "This is not an easy test to read." In the ACRIN trial, participating radiologists were required to submit evidence of having interpreted at least 500 CTC examinations or to complete a special course. In either case, participants had to pass a qualifying exam.

A number of training courses are now offered by groups such as ACR and the Society of Gastrointestinal Radiologists (SGR) and by some institutions, such as the University of Chicago, New York University and the University of California, San Francisco. The ACR course is similar to that required for the trial, with 50 hands-on case studies designed to address specific issues in reading CTC scans. When trainees successfully complete the 50 cases, they receive a certificate of proficiency that shows they meet ACR guidelines. The certificate can help radiologists meet the credential requirements of hospitals and third-party payers. SGR anticipates providing a certification with its annual course in 2009.

In one sign of the rising importance of CTC training, the International Symposium on Virtual Colonoscopy will be held next year at ACR headquarters in Reston, Va., in conjunction with one of the group's colonography courses.

The ACRIN trial results are also expected to affect reimbursement policies. The Centers for Medicare & Medicaid Services (CMS) launched a national coverage analysis to study the impact and readiness of widespread CTC colorectal cancer screening in the U.S. The analysis is scheduled to be completed in early 2009.

One of the largest private payers in the U.S., United Healthcare, now covers CTC for screening, while the Blue Cross, Blue Shield Association and a number of other insurers are also considering or have approved coverage. "The number is changing daily," said Matthew Barish, M.D., director of CTC at the State University of New York, Stonybrook, who designed and directs the ACR course.

There is growing concern about managing unsuspected extracolonic malignancies detected at screening CT colonography (CTC), as CTC use increases in light of studies validating its accuracy. A low-dose unenhanced transverse two-dimensional image (a) from screening CTC in an asymptomatic 50-year-old man shows massive abdominal lymphadenopathy and splenomegaly. The findings are better depicted on an image (b) from the subsequent diagnostic staging CT study of the chest, abdomen and pelvis. Mantle cell non-Hodgkin lymphoma was confirmed at percutaneous core needle biopsy. (c) The patient achieved complete remission with chemotherapy and was free of evidence of disease 2 years after diagnosis. Radiology 2008;249:151-159. © RSNA, 2008. All rights reserved. Reprinted with permission.

Extracolonic Findings are Complicated, Controversial

One of the more complicated and controversial practice issues related to CTC is how to manage extracolonic findings. CTC imaging includes parts of the lungs, kidneys and abdominal organs, and abnormalities turn up on many scans. Some, such as lung nodules, renal masses and aortic aneurysms, are potentially life threatening. About 16 percent of patients in the ACRIN trial had extracolonic findings that were worrisome enough to trigger further testing or urgent care.

Robert Fletcher, M.D., a professor emeritus of ambulatory care and prevention at Harvard Medical School in Boston, wrote an editorial to accompany the NEJM article, questioning the benefit of identifying and following up on these abnormalities. "Although some extracolonic findings are life-threatening, few (with the exception perhaps of unrecognized abdominal aortic aneurysms) can be treated effectively," Dr. Fletcher wrote.

The federal government's U.S. Preventive Services Task Force (USPSTF) also cited the problem of extracolonic findings in its recent decision not to recommend CTC for colorectal cancer screening. "Evidence to assess the harms related to extra-colonic findings is insufficient and the balance of benefits and harms cannot be determined" the task force reported in October.

Others contend that patients do benefit when a potentially dangerous mass or aneurysm is found. The main issue now is establishing protocols for managing extracolonic findings, said Dr. Johnson. "We need evidence-based rules for interpretation, indicating when there is a need and when there is no need to report or follow up," he said. A study based on the ACRIN results is already under way to increase understanding of these issues, he added.

Radiation exposure has been raised as another potential disadvantage to regular CTC screening. The USPSTF reported exposure of about 10 mSv per examination and that the harm at this level is uncertain. Other experts point out, however, that current ACR guidelines call for lower doses, making the effective radiation dose 6–8 mSv per exam. "This is approximately the same as a double-contrast barium enema," said Judy Yee, M.D., a professor and vice-chair of radiology and biomedical imaging at the University of California, San Francisco. "The USPSTF has raised undue alarm. It is short-sighted and a disservice to patients who otherwise won't come in for screening at all."

Patient Compliance Still a Barrier

Getting patients in for colonoscopy is one of the major barriers to regular screening. CTC eliminates some of the inconvenience associated with colonoscopy, such as the need for sedation. It requires the same arduous 24-hour bowel cleansing, however, and the patient has to undergo a standard colonoscopy if polyps are found. The subsequent colonoscopy requires another day of colon cleansing unless a colonoscopy appointment can be arranged the same day.

"A team of radiologists and gastroenterologists is required in order to provide the best service to patients," Dr. Johnson said. "I think we can solve this." At Mayo, the gastroenterology department now keeps a few appointments open each day for patients whose CTC scans indicate they need a colonoscopy, he said, while the radiology department does the same for cases in which a standard colonoscopy cannot be completed.

Another way to deal with a lack of patient compliance could be to develop less difficult, non-cathartic ways to prepare the colon for CTC, said Dr. Johnson. Studies are looking at the use of a contrast medium that would allow radiologists to reliably discriminate stool from polyps, he added.

If these studies are successful, patient acceptance of screening in general and the use of CTC in particular is expected to increase dramatically, which should result in more screening and more lives saved, said Dr. Johnson.

"If the preparation gets figured out, it will be revolutionary," he said.