Longer CT Colonography Screening Interval May Be Safe, Analysis Suggests

Posted on October 2016

A new analysis of screening intervals for CT colonography (CTC) found that it may be safe to wait as long as five to ten years to screen again after an initial negative scan. The results are good news for the cost-effectiveness profile of CTC, investigators report in Radiology.

The group from the University of Wisconsin-Madison led by Drs. Perry Pickhardt, Dustin Pooler (4th year resident), and David Kim of the Department of Radiology, Dr. Ifeanyi Mbah of the Department of Obstetrics and Gynecology, and Dr. Jennifer Weiss of the Department of Medicine, analyzed results from 1,429 patients who returned for repeat screening CTC more than five years, on average, after their initial negative CTC exam. They compared the CTC findings at follow-up with the initial screening and found fewer advanced lesions than usual and just two small cancers in the cohort.

Pickhardt and colleagues analyzed the results of all patients who had positive findings at follow-up, comparing them with the initial CTC results. Positive findings were defined as polyps 6 mm or larger, a threshold that typically requires follow-up.

At follow-up CTC, the percentage of patients with positive results (12.1%) was lower than the percentage of patients (14.3%) who were positive on initial screening.

“The interval cancer rate at routine CT colonography surveillance was lower than the cancer rate seen at initial screening, as well as the reported interval rates at [optical colonoscopy],” the team wrote.

The results support the five- to ten-year screening interval for CTC suggested in the 2005 CT
Colonography Reporting and Data System (C-RADS) recommendations from the University of Wisconsin-Madison, according to lead author and Professor of Radiology Dr. Perry Pickhardt. “Going beyond five years further improves cost-effectiveness,” he added.