Validation of automated script-based proton therapy optimisation for comparative head and neck planning.

Background and purpose: Proton and photon plan comparison is often the gateway to proton therapy for head and neck cancer (HNC). Manual planning is resource demanding, whereas automated planning may efficiently create consistent treatment plans. An automated rule-based intensity-modulated proton therapy (IMPT) plan optimisation script was developed within a commercial treatment planning system for comparative planning. This study benchmarked automated against clinical plans and evaluated whether a standard or patient-specific field set-up was necessary. Materials and methods: Twenty HNC patients previously treated with IMPT using manual plans were included. For each patient, two automated IMPT plans were generated, differing in field set-up: one with a standard five-field set-up and one matching the clinical field set-up. Robustness, dose distribution, and normal tissue complication probability (NTCP) for dysphagia and xerostomia were compared. Results: On average, automated IMPT plans were created in 64 min. Compared with clinical plans, both automated plan types, generally, reduced organ of interest mean doses, with median differences of up to 3.3 Gy (glottis). Automated plans also had lower median NTCP for dysphagia of 0.1%-points (interquartile range (IQR): -0.8-0.9) and 0.3%-points (IQR: 0.0-0.6) for standard and clinical field set-ups, respectively. For xerostomia, the corresponding results were 0.3%-points (IQR: 0.0-1.5) and 0.3%-points (IQR: 0.1-0.8), respectively. Conclusions: The IMPT plan optimisation script created plans with comparable robustness, dose distribution, and NTCP to clinical plans and is applicable for selecting HNC patients for IMPT. Additionally, a standard field set-up was adequate for comparative planning for most patients.