Abstract
BACKGROUND AND PURPOSE: One barrier to wider clinical implementation of online MRI-guided radiotherapy (MRIgRT) on the MR Linac (MRL) is resource intensity. Specifically, the requirement for a clinical oncologist/radiation oncologist (CO/RO) to perform online contouring each fraction. We report an evaluation of therapeutic radiographer (RTT) online contouring for patients receiving whole bladder MRIgRT. MATERIALS AND METHODS: RTTs undertook a contouring training programme. RTT and CO/RO clinical target volume (CTV) contours from 95 fractions were assessed using dice similarity coefficient (DSC), hausdorff distance (HD), mean distance to agreement (MDA), sensitivity and specificity volume metrics on the Raystation treatment planning system (TPS) (RaySearch Laboratories). Additionally, CTV DSC was evaluated with respect to a simultaneous truth and performance level estimation (STAPLE) generated in ADMIRE (Elekta AB, Stockholm, Sweden). In dosimetric analysis (Monaco, Elekta AB), online adaptive treatment plans, which had been generated using RTT-defined contours, were evaluated using contours delineated offline by CO/ROs. RESULTS: Comparison of RTT versus CO/RO contours found the CTV median (interquartile range) (IQR) for DSC was 0.92 (0.91-0.94), MDA was 0.11 (0.09-0.12) cm, and HD was 0.63 (0.53-0.72) cm, sensitivity and specificity were 0.94 (0.90-0.96) and 0.95 (0.92-0.97) respectively. In dosimetric analysis, 65 % (30/46) plans met optimal PTV coverage of V52.25 Gy > 98 % and all plans met mandatory PTV coverage of V52.25 Gy > 95 %. CONCLUSION: Following effective training, evaluation results demonstrate RTT whole bladder CTV contours to be comparable to CO/RO contours. Clinical implementation will release CO/ROs from MRL bladder treatments, reducing resource intensity of online workflows.