Performance and Evaluation in Computed Tomographic Colonography Screening for Colorectal Cancer

Each year over 20,000 people die from colorectal cancer (CRC). However, despite causing the second highest number of cancer deaths, CRC is not only curable if detected early but can be prevented by population screening. The detection and removal of pre-malignant polyps in the colon prevents cancer from ever developing. As such, screening of the at-risk population (those over 45-50 years) confers protection against CRC incidence and mortality. Although the principles and benefit of screening are well established, the adequate provision of screening is a complex process requiring robust healthcare infrastructure, evidence-based quality assurance and resources. The success of any screening programme is dependent on the accuracy of the screening investigations deployed and sufficiently high uptake by the target population. In England, the Bowel Cancer Screening Programme (BCSP) delivers screening via initial stool testing to triage patients for the endoscopic procedure, colonoscopy, or the radiological investigation CT colonography (CTC) in some patients. There has been considerable investment in colonoscopy accreditation processes which contribute to high quality services, suitable access for patients and a competent endoscopy workforce. The performance of colonoscopists in the BCSP is tightly monitored and regulated; however, the same is not true for CTC. Comparatively, there has been little investment in CTC services, and in fact there is no mandatory accreditation or centralised training. Instead, CTC reporting radiologists must learn ad hoc on the job, or at self-funded commercial workshops. This inevitably leads to variability in quality and expertise, inequity in service provision, and could negatively impact patient outcomes. To address this disparity and develop evidence-based training, one must determine what factors affect the performance of CTC reporting radiologists, what CTC training is necessary, and what training works. This thesis investigates these topics and is structured as follows: Section A reviews the background literature, describing the public health burden of CRC and the role of screening. Aspects of CTC screening and its role in the BCSP are explored. The importance of performance monitoring and value of accreditation are examined and the disparity between CTC, colonoscopy and other imaging-based screening programmes is discussed. Section B expands on radiologist performance by determining the post-imaging CRC (or interval cancer) rate through systematic review and meta-analysis. Factors contributing to the interval cancer rate are evaluated, and an observational study assessing factors affecting CTC accuracy is presented. The impact of CTC training is assessed via a structured review and best principles for training delivery are discussed. Section C presents a multicentre, cluster-randomised control trial developed from the data and understanding described in Sections A and B. Section D summarises the thesis and discusses future recommendations and research