Noncathartic CTC useful tool for colorectal cancer detection

Noncathartic CT colonography (CTC) could be helpful in detecting colorectal cancer and polyps, particularly in frail patients or in those unwilling to undergo bowel preparation, according to a study published in the October issue of the American Journal of Roentgenology.

Colorectal cancer screening is often hindered by cathartic bowel preparation, with 40 percent of the U.S. population older than 50 failing to undergo screening.  

“Purgation bowel cleansing is a major disincentive to colorectal cancer screening at colonoscopy,” wrote the study’s author, Joel G. Fletcher, MD, of the Mayo Clinic in Rochester, Minn., and colleagues. “CTC has been endorsed as an accepted method of full structural colorectal cancer screening and may improve colorectal cancer screening rates but currently requires a cathartic bowel preparation.”

Based on this difficulty, the authors designed a prospective study to examine the image quality and performance of noncathartic CTC with four similar bowel-tagging regimens using standard noncathartic CTC visualization techniques in an asymptomatic screening cohort.

Five hundred sixty-four participants were recruited from asymptomatic patients who had been referred for colonoscopy. All subjects ingested 21 grams of barium sulfate over two days before the exam and an additional 250 mL of four percent barium suspension the morning of the noncathartic CTC procedure.

Four regimens were conducted with or without iodinated oral contrast materials. The quality of tagging with oral agents was then evaluated with primary 2D search supplemented by electronic cleansing (EC) and 3D problem solving. Results were compared with complete colonoscopy findings after bowel purgation and with retrospective unblended evaluation in 556 of the 564 participants.

Results indicated that seven percent of the study population had 52 adenomatous polyps 6 mm or larger, and three percent had 20 polyps that were 10 mm or larger. The incorporation of iodine significantly improved the percentage of labeled stool at image quality assessment and boosted reader specificity in identifying colorectal polyps at noncathartic CTC.

The overall sensitivity for noncathartic CTC for adenomatous polyps 6 mm or greater was 76 percent, a finding similar to the sensitivity of the iodinated regimens with most patients. The negative predictive value was 98 percent and the only cancer was detected. The researchers believe that EC improved the prominence of ten of the 21 visible polyps that were 10 mm or greater.

“Including iodine tagging agents substantially improves tagging of particulate stool and examination specificity. Additional improvements in performance might be realized by further refinements in electronic stool subtraction, double-reading, dietary restriction to low-fiver foods before examination, and development of CAD for the minimally prepared colorectum,” the authors wrote.