Reader training in CT colonography: how much is enough?

Although computed tomographic (CT) colonography is increasingly being recognized as a legitimate method of detecting colorectal neoplasia (1), an important condition for the broad acceptance of this examination will be the assurance of high-quality standards of performance and interpretation. As the technique continues to evolve and improve, its use is shifting from highly specialized academic centers to community hospitals and nonacademic radiology practices. Many radiologists are experiencing pressure from clinical colleagues to offer CT colonography as part of the routine services provided in their practices. However, CT colonography is not just an extension of CT performed for other indications; therefore, as with the training required before any new technique is applied, radiologists who are currently in practice should not be expected to be able to perform CT colonography or interpret the resultant findings without additional training. There is emerging consensus that one of the most important factors affecting the diagnostic performance of CT colonography is the training and experience of the radiologist interpreting the examination (1). In a survey conducted among the majority of the members of the Working Group in Virtual Colonoscopy, an ad hoc group of investigators active in the area of CT colonography, the 18 respondents unanimously concurred that specific training is needed to interpret CT colonographic findings (2). The same group suggested that the most advisable method of training readers is an intensive hands-on course conducted at reading workstations with the supervision of experienced radiologists and by using exclusively cases with optical colonoscopy proof. During this training course, each reader should independently interpret between 40 and 50 cases that include examples of normal CT colonographic findings and a wide variety of lesion sizes and morphologic features, as can be expected in actual clinical practice. The premise is that this experience will allow the reader to become familiar with the various methods available for the primary interpretation of CT colonographic data sets while teaching him or her to recognize the technical variables and potential interpretation pitfalls that may affect the diagnostic performance of the examination. Formal lectures in which data supporting the use of CT colonography for colon screening are reviewed and that include discussions addressing patient preparation, technical acquisition parameters, interpretation techniques, and issues not related to interpretation are also advisable. There is also emerging consensus that there is a variable learning curve associated with interpreting CT colonographic findings. This implies that interpretation performance improves as the number of interpreted cases increases. Although this may be true as a general statement, it is very likely that the specific characteristics of the curve vary between observers. Evidently, every observer will eventually reach an individual plateau of maximal performance. For example, in the multicenter trial conducted by Pickhardt et al (3,4), there was no significant difference in the diagnostic performance of the six readers when the four quartiles were analyzed separately. Thus, in that trial, every reader achieved a plateau of maximal performance after enrollment of 25% (approximately 50 patients per reader) of the patients. Interpretation of CT colonographic findings entails a meticulous evaluation of the complete luminal surface of the colonic wall. Since this search pattern may be unfamiliar to most inexperienced observers, it is possible that some individuals, irrespective of how many cases they evaluate during the training process, may not ever reach the desired plateau of maximal performance. In other words, there is no guarantee that a given reader will achieve an adequate performance level by completing training sessions (5). Even if the desired performance level is to be reached, the slope of the curve may vary considerably between readers—from very steep (rapid improvement in performance with increasing training) to very shallow (slow improvement with increasing training). Moreover, the slope of the curve may vary according to the method used for primary interpretation (two-dimensional vs three-dimensional), even for the same individual. The starting point of the curve may also vary between observers. Readers with little or no experience in abdominal CT may require more specific training in CT colonography before they reach the optimal performance goals (6) compared with readers who have extensive experience in crosssectional imaging of the abdomen and bowels. Unfortunately, the lack of standards and uniformity in reader training and prior experience has plagued the prospecPublished online 10.1148/radiol.2371050003 Radiology 2005; 237:26–27