JNM: Non-laxative PET/CTC might be particularly beneficial for elderly

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PET combined with CT colonography (CTC) may provide a suitable alternative for detecting polyps and cancer in the colon, and the lack of bowel prep might be particularly beneficial in the elderly population, a study published in the June issue of the Journal of Nuclear Medicine shows.

This particular imaging method may be especially desirable for patients because it does not require sedation or bowel preparation. The authors said the main goal of their study was to test the technical feasibility and patient acceptance of non-laxative PET/CTC.

"One of the first indications of colorectal cancer is often the presence of polyps, which are abnormal tissue growths on the inner lining of the colon or large intestine," said lead author Stuart A. Taylor, MD, University College London. "If these polyps are detected non-invasively and without the use of bowel preparation and sedatives, investigation can be much easier on patients who would otherwise undergo colonoscopies."

Although the standard diagnostic technique of optical colonoscopy is very effective, it is “invasive and can be uncomfortable for patients, as they need to empty their bowel using laxatives beforehand, they may require sedation during the test and may need to take a whole day off from their normal activities,” according to the authors, who added that strong laxatives can also be harmful to older patients, as they may cause dehydration.

The researchers studied 56 patients (median age of 64 years; 30 women) at high risk of colonic neoplasia who underwent non-laxative PET/CTC with barium fecal tagging, who agreed to undergo the procedure within two weeks of their scheduled colonoscopy. Colonic segmental distension was graded as one (poor) to three (good).

In consensus, a radiologist, experienced in CTC, and nuclear medicine physician analyzed the datasets. The diagnostic performance for standalone CTC and combined PET/CT colonography was compared with the reference colonoscopy. The investigators also canvassed patient experience for 25 items (each scored from one to seven) pertaining to satisfaction, worry and physical discomfort after both PET/CTC and colonoscopy.

Distension was good in 84 percent of 334 segments, Taylor and colleagues reported. Patients experienced more physical discomfort during colonoscopy (median, four) than during PET/CTC (median, five) and were more willing to undergo PET/CTC again (84 vs. 72 percent).

According to the authors, 21 patients had 54 polyps according to colonoscopy (10 with at least one polyp, at least 6 mm and eight with at least one polyp at least 10 mm). Of 14 polyps 6 mm or greater, 12 (86 percent) were 18F-FDG–avid, including all those 10 mm or greater (mean standardized uptake value, 10.1).

CTC sensitivity for polyps 6 mm or larger was 92.9 and was not improved by the addition of PET. However, the researchers reported that the combined PET/CT colonography review improved per-patient positive predictive value for a polyp 10 mm or greater from 73 percent to 100 percent.

They also found an additional benefit of cross-sectional imaging in older symptomatic patients is the ability to assess extracolonic organs: they detected an unsuspected gastric tumor, for example.

Furthermore, the authors wrote that the additional specificity “afforded by PET potentially has beneficial effects on cost effectiveness. In the current study, an indeterminate adrenal mass and presacral soft-tissue thickening were both non- 18F-FDG–avid and subsequently proven benign on further work-up, which was arguably unnecessary.”

“The work has shown that combined PET/CTC is technically feasible, well tolerated by patients and capable of achieving high diagnostic accuracy," said Taylor. "This test would be mainly used in patients less able to tolerate invasive investigations or the preparation required if physicians want to exclude any major pathology in the colon and abdomen.”