ESTRO 2025 - Abstract Book

S1609

Clinical – Mixed sites & palliation

ESTRO 2025

Proton therapy (PT) is a tool that may facilitate finding solutions to this problem and PT delivery with discrete Proton Arc Therapy (PAT) may further increase the therapeutic ratio

Material/Methods: Before starting clinical PAT treatments, comprehensive commissioning of the technique was performed. 10 H&N cancer patients were selected and both PAT and MultiFieldOptimization (MFO) plans were compared regarding nominal dose distributions, robustness, NTCP endpoints and replanning frequency. Four patients with ECOG performance status 0 were selected to receive PAT as a significant dosimetric benefit was likely. No concomitant chemotherapy was prescribed. For all patients a standard MFO plan was prepared as the state-of-the-art baseline and for further comparisons. All patients had control CT scheduled during the course of their treatment to detect changes in delivered dose as a consequence of patient conformation changes etc. For the first two patients with lateralized lesions, PAT plans were created with a half arc (from 180° to 0°) with clockwise gantry rotation. The remaining two patients were treated with a complete arc (360°) with 20 beam directions. All technical data are summarized in Table1

Results: Patient and treatment characteristics are described in Table2 in terms of disease type, stage, clinical target volumes, radiation course, prescribed dose and status of their treatment. Prescription doses and OAR constraints were chosen according to international guidelines. Two patients have already completed their treatment without treatment breaks and without unexpected acute toxicity. Dosimetric data of the plan comparison are shown in Table1, focussing on the clinically most relevant dose-volume parameters. A clear superiority of PAT plans compared to the “state -of-the- art” MFO plans is observed