Results of the Australasian (Trans-Tasman Oncology Group) radiotherapy benchmarking exercise in preparation for participation in the PORTEC-3 trial

Introduction Protocol deviations in Randomised Controlled Trials have been found to result in a significant decrease in survival and local control. In some cases, the magnitude of the detrimental effect can be larger than the anticipated benefits of the interventions involved. The implementation of appropriate quality assurance of radiotherapy measures for clinical trials has been found to result in fewer deviations from protocol. This paper reports on a benchmarking study conducted in preparation for the PORTEC‐3 trial in Australasia. Methods A benchmarking CT dataset was sent to each of the Australasian investigators, it was requested they contour and plan the case according to trial protocol using local treatment planning systems. These data was then sent back to Trans‐Tasman Oncology Group for collation and analysis. Results Thirty three investigators from eighteen institutions across Australia and New Zealand took part in the study. The mean clinical target volume (CTV) volume was 383.4 (228.5–497.8) cm3 and the mean dose to a reference gold standard CTV was 48.8 (46.4–50.3) Gy. Conclusions Although there were some large differences in the contouring of the CTV and its constituent parts, these did not translate into large variations in dosimetry. Where individual investigators had deviations from the trial contouring protocol, feedback was provided. The results of this study will be used to compare with the international study QA for the PORTEC‐3 trial.