Automated multi-criterial treatment planning for adaptive high-dose-rate brachytherapy for locally advanced cervical cancer

Purpose - To develop and evaluate a fast and automated multi-criterial treatment planning strategy for High-Dose-Rate (HDR) brachytherapy (BT) for patients with locally advanced cervical cancer. This automated strategy avoids suboptimal and slow manual treatment planning and results in reproducible and conformal treatment plans with a clinically favorable trade-off between multiple treatment objectives. Methods and Materials - An automated treatment planning approach was developed using the Erasmus- iCycle framework. A wish-list containing hard constraints and prioritized objectives is required as input was configured according to the clinical protocol using 22 single-fraction training plans. Special at- tention was paid to establishing the clinically desired ‘pear-shaped’ dose distribution. To evaluate the dwell time optimization approach, 66 automatically generated single-fraction plans (PLANauto) were compared against the clinically delivered plans (PLANref ), both by blind-pairwise comparison carried out by an expert clinician and by the analysis of dosimetric plan parameters. Subsequently, for 17 complete fractioned BT treatments each consisting of 3 single-fraction BT plans, automatically generated plans (TREATMENTauto) were compared against the clinically delivered plans (TREATMENTref) to evaluate dosimetric plan parameters according to the clinical protocol. The possibility of extending the algorithm with a needle selection objective was also explored on 13 test cases and its performance was evaluated by studying the number of needles selected in the optimized plans and its effect on the remaining treatment objectives.Results - All PLANauto were considered clinically acceptable by the clinician. The clinician’s plan comparison pointed strongly at an overall preference for the automated plans: in 62/66 cases the clincian preferred PLANauto over PLANref , in three cases the overall quality was considered equal and for one case the clinical plan was preferred. For PLANauto, the mean HR-CTV D90% improved while also the rectum was spared compared to PLANref . The average optimization time was 19.5 seconds (range [4.4 – 106.4] s). The mean D90% for TREATMENTauto improved by + 3.0 Gy (in EQD2) (pl0.005) over the whole radiotherapy treatment with differences ranging from -4.3 to +6.0 Gy, while the bladder and rectum were spared similarly (p=0.01, p=0.02 respectively). In 6/13 of the plans, the number of needles that were implanted could be reduced while still establishing sufficient plan quality. Conclusions - Fast automated multi-criterial treatment planning for locally advanced cervical cancer HDR-BT is feasible. High-quality treatment plans are automatically generated within a clinically acceptable time frame and treatment plans have a clinically preferable trade-off between all treat- ment objectives. The observed improvement in dosimetric parameters, mainly the improvement of the dose to the HR-CTV, is clinically relevant. The algorithm can be extended with an approach for the optimization of the implant geometry, which could allow interactive intra-operative treatment planning.