Bayesian methods provide a practical real-world evidence framework for evaluating the impact of changes in radiotherapy

Purpose: Retrospective studies have identified a link between the average set-up error of lung cancer patients treated with image-guided radiotherapy (IGRT) and survival. The IGRT protocol was subse-quently changed to reduce the action threshold. In this study, we use a Bayesian approach to evaluate the clinical impact of this change to practice using routine 'real-world' patient data.Methods and Materials: Two cohorts of NSCLC patients treated with IGRT were compared: pre-protocol change (N = 780, 5 mm action threshold) and post-protocol change (N = 411, 2 mm action threshold). Survival models were fitted to each cohort and changes in the hazard ratios (HR) associated with residual set-up errors was assessed. The influence of using an uninformative and a skeptical prior in the model was investigated.Results: Following the reduction of the action threshold, the HR for residual set-up error towards the heart was reduced by up to 10%. Median patient survival increased for patients with set-up errors towards the heart, and remained similar for patients with set-up errors away from the heart. Depending on the prior used, a residual hazard ratio may remain.Conclusions: Our analysis found a reduced hazard of death and increased survival for patients with resid-ual set-up errors towards versus away from the heart post-protocol change. This study demonstrates the value of a Bayesian approach in the assessment of technical changes in radiotherapy practice and sup-ports the consideration of adopting this approach in further prospective evaluations of changes to clinical practice.Crown Copyright (c) 2022 Published by Elsevier B.V. Radiotherapy and Oncology 176 (2022) 53-58 This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

The study compared two cohorts of NSCLC patients treated with IGRT before and after a protocol change, finding a reduced impact of set-up errors on the heart after the threshold reduction. The Bayesian approach used in the analysis demonstrated increased survival for patients with residual set-up errors towards the heart, supporting its consideration in future evaluations of clinical practice changes.