Understanding CTC screening

Utilization of CT colonography (CTC) has been increasing as interest grows over the benefits compared with standard colonoscopy. Cost, minimal invasiveness and the fact that it’s well-tolerated by patients makes it an attractive option for most.

Despite the growing enthusiasm, and the establishment in 2005 of the CT Colonography Reporting and Data System (C-RADS), no large-scale studies had previously been conducted to act as a reference point for the distribution of C-RADS categorizations within a clinical screening program.

That changed with a study published in the June issue of the American Journal of Roentgenology. B. Dustin Pooler, MD, of the University of Wisconsin School of Medicine and Public Health in Madison, and colleagues sought to offer an initial benchmark for C-RADS classification that could be used by other programs as a comparison and also to facilitate quality assurance measures.

They prospectively classified CTC results according to C-RADS over a seven year period, which included 6,769 asymptomatic adults between the ages of 50 and 79. Results showed that 14.3 percent of the subjects were positive (C-RADS classification C2 through C4), with positive findings more common in men than women (17.5 percent vs. 11.6 percent). Positive classifications also increased with age, as 13.4 percent of patients between 50 and 64 were positive, compared with 21.8 percent of patients between 65 and 79. A total of 86.6 percent of patients had negative or unimportant extracolonic findings.

A separate study, published online May 22 in Radiology, also included in the month’s top stories focused on that question of extracolonic findings. CTC can inadvertently image extracolonic abdominal and pelvic tissue, and the handling of extracolonic screening is a subject for debate.

“It is unclear how individual patients and health care professionals balance the possibility of detecting life-threatening extracolonic pathologic findings against the larger chance of fruitless (or even harmful) testing precipitated by extracolonic findings,” wrote lead author Andrew A. Plumb, MA, MRCP, FRCR, of University College Hospital in London, and colleagues.

To determine patients and healthcare professionals’ tolerance for false-positives in the detection of extracolonic malignancy using CTC, Plumb and colleagues conducted choice experiments featuring 52 patients and 50 healthcare professionals. One experiment presented subjects with varying scenarios for false-positive rates, while another examined radiologic follow-up compared to invasive follow up.

Participants were much more likely to tolerate high rates of false-positives when it meant radiologic follow up compared with invasive follow up, and patients were more tolerant than healthcare professionals. Patients would accept false-positive rates of up to 99.8 percent for either type of follow up to detect extracolonic malignancies, while healthcare professionals capped their false-positive tolerance at 40 percent and 5 percent for radiologic and invasive follow up, respectively.

As more patients become educated on CTC, studies like the ones conducted by Pooler et al and Plumb et al will be invaluable to understand screening practices.

-Evan Godt
Editor – Health Imaging