ESTRO 2025 - Abstract Book

S3537

Physics - Optimisation, algorithms and applications for ion beam treatment planning

ESTRO 2025

3472

Digital Poster Robustness, RBE and treatment times in clinical proton arc therapy treatment planning for neuro oncological patients Koen F Crama 1,2 , Pelagia Fotiadou 3 , Danny Lathouwers 4 , Jasper Kouwenberg 5 , Steven J.M. Habraken 1,5 1 Radiotherapy, Leids University Medical Centre, Leiden, Netherlands. 2 Radiotherapy, HollandPTC, Delft, Netherlands. 3 Mechanical Engineering, TU Delft, Delft, Netherlands. 4 Delft University of Technology, Department of Radiation Science and Technology, TU Delft, Delft, Netherlands. 5 Medical Physics and Informatics, HollandPTC, Delft, Netherlands Purpose/Objective: Proton arc therapy (PAT) holds the promise to further reduce dose to healthy tissue and improve LET/RBE distributions. In this study, we investigated the impact of various discrete PAT planning approaches on robustness and LET/RBE in grade III glioma patients. Material/Methods: We included 10 patients, treated with IMPT to 59.4 Gy(E) in 33 fractions at our center. Six robust discrete PAT techniques with 6, 9, 18 and 27 discrete PAT beam directions were used. Plans with and without a 3cm range shifter (RS) were made for the latter two and increasing numbers of energy layers were used. Based on our clinical protocol, 28 scenerios were evaluated with 3mm setup and 3% range robustness. Clinical goals were assessed on individual scenarios, as well as on Vmin/Vmax dose distributions. Nominal RBE-weighted dose was compared between the McNamara model and a fixed RBE of 1.1, as used clinically. Treatment times were calculated based on measured delivery speeds in MU/s, energy layer switching times and pencil-beam scanning speeds. Results: Median treatment times of 5, 11, and 30 minutes were found for the clinical, 9-beam and 30-beam PAT plans respectively. Differences in robust CTV coverage (V95%), particularly in plans where a trade-off between target dose and OAR dose was neccessary, were observed in the PAT plans (Figure 1)