Radiology: 175 exams yields sufficient CT colonography training

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With CT colonography gaining acceptance as an alternative to colorectal cancer screening via colonoscopy, researchers have concluded that an average of 175 studies may amount to sufficient training for novice radiologists and technicians reading the images, according to a study published in the February issue of Radiology.

CT colonography (CTC) screening for colorectal cancer is growing in use, with studies demonstrating sensitivities to larger polyps comparable to colonoscopy but with the potential for greater compliance due to CTC’s less-invasive nature. “So far, no consensus exists about the level of experience needed and how the desired level can be best acquired” for accurate CTC screening, with some studies suggesting that CTC is a relatively hard technique to learn, explained Marjolein H. Liedenbaum, MD, of the department of radiology at the Academic Medical Center Amsterdam, University of Amsterdam, and colleagues.

“The aim of our study was to determine how many CT colonography training studies have to be evaluated by novice readers to obtain an adequate level of competence in polyp detection,” Liedenbaum and colleagues continued. The authors selected 200 CTC exams, allocating 50 exams to four different phases of review to track readers’ progress in detecting polyps.

Half of the studies in each group contained polyps or carcinomas larger than 6 mm, with 10 of these studies per group showing lesions larger than 10 mm. Within these strata, the studies were randomly ordered and read by nine novice readers, which consisted of one radiologist, three radiology residents, two radiology researchers (pre-residency medical doctors) and three technicians. None of the readers had previous experience reading CTC.

Training consisted of two articles on the pitfalls of CTC and a basic 2.5-hour course including anatomy, colon disease information and CTC viewing instruction. Afterwards, all trainees reviewed 4 CTC exams under the guidance of a CTC research fellow, lasting four hours, followed by a subgroup of five readers receiving an additional hour of pitfalls and polyps training.

Overall sensitivity per 6 mm or larger polyps was 76 percent for exams 1 through 50; 77 percent for exams 51 through 100; 80 percent for 101 through 150; and 91 percent for exams 151 through 200. The difference in specificity between the first and fourth set of exams differed significantly. For lesions 10 mm or greater, these values were 83 percent, 96 percent, 96 percent and 96 percent, respectively, with the first and second group showing a significant difference.

On a per-patient basis, overall sensitivities for exams 1 through 50, 51 through 100, 101 through 150 and 151 through 200 were 90 percent, 82 percent, 96 percent and 93 percent for lesions greater than 6 mm, respectively. For neoplasia (carcinomas and adenomas) 6 mm or larger, the sensitivities were 91 percent, 84 percent, 97 percent and 91 percent, respectively.

The authors observed that “it is apparent that almost all readers first had an increase in sensitivity, then had a slight decrease or plateau phase after 80 to100 CT colonographic examinations, and then sensitivity increased again.”

Based on an a prior determination that sufficient performance demanded 95 percent sensitivity to lesions 10 mm or larger and 90 percent sensitivity for lesions 6 mm or larger, trainees reached these values after an average of 164 exams. This led the researchers to conclude: “The results showed that these novice readers can reach sensitivity equal to that of an experienced reader after practicing with 175 training CT colonographic studies with colonoscopy feedback and a lesion prevalence of 50 percent of CT colonographic studies with at least one lesion 6 mm or larger.”

The authors also found that the extra training given to five readers had no effect on sensitivity, though it was associated with improved specificity on lesions 6 mm or larger.

Liedenbaum and colleagues acknowledged that their small sample size of readers did not permit them to determine differences between trainees as contributing to varying sensitivities and specificities.

The authors concluded by saying, “[W]e found that CT colonography interpretation can be adequately performed after a computer training program by inexperienced radiologists, radiology fellows and radiology technicians. On average, training with 164 CT colonographic examinations with colonoscopic verification was required in this specific training setting