Yield and Cost-effectiveness of Computed Tomography Colonography Versus Colonoscopy for Post Colorectal Cancer Surveillance

Purpose. As part of a clinical trial comparing the utility of computed tomographic colonography (CTC) and optical colonoscopy (OC) for post colorectal cancer resection surveillance, we explored the diagnostic yield and costs of a strategy of CTC followed by OC if a polyp is observed (abbreviated CTC_S), versus OC 1 year following curative bowel resection, using the detection of actionable polyps on OC as the criterion. Methods. Using data from 231 patients who underwent same-day CTC followed by OC, we created a decision tree that outlined the choices and outcomes at 1-year clinical follow-up. Colorectal polyp prevalence, sensitivity, and specificity of CTC were compared with five exemplary studies and meta-analyses. Detection criteria were derived for ≥6 mm or ≥10 mm polyps. OC was the gold standard. Costs were gleaned from cataloging components of the cases at the principal investigator’s institution. Analyses included marginal cost of the OC strategy to detect additional actionable polyps and number of polyps missed per 10,000 patients. Results. At our prevalence of 0.156 for ≥6 mm (0.043 ≥10 mm), CTC_S would miss 779 ≥6 mm actionable polyps per 10,000 patients (≥10 mm: 173 per 10,000). Cost to detect an additional ≥6 mm polyp in this cohort is $5,700 (≥10 mm: $28,000). Sensitivity analyses demonstrate that any improvement in performance characteristics would raise the cost of OC to detect more actionable polyps. Similar results were seen using Medicare costs, or when literature values were used for performance characteristics. Conclusion. At an action threshold of ≥6 mm, OC costs at least $5,700 per extra polyp detected relative to CTC_S in patients undergoing surveillance after colorectal cancer surgery, on the order of incremental cost-effectiveness ratios found for other clinical problems involving short-term events.