ESTRO 2025 - Abstract Book

S3466

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

ESTRO 2025

1425

Digital Poster A Novel Treatment Modality Spot Scanning Proton Arc (SPArc) Therapy for Tumor Dose-Response Guided Adaptive Dose Escalation Shupeng Chen 1 , Jun Zhou 1 , Xiaoda Cong 2 , Xuanfeng Ding 2 , Rohan Deraniyagala 2 , Craig Stevens 2 1 Radiation Oncology, Emory University, Atlanta, USA. 2 Radiation Oncology, Corewell Health, Royal Oak, USA Purpose/Objective: Large tumor heterogeneity poses significant challenges for dose escalation in advanced head and neck squamous cell carcinoma (HNSCC) patients using conventional photon therapy. This study investigated the potential dosimetric advantages of proton therapy, specifically including intensity modulated proton therapy (IMPT) and spot scanning proton arc (SPArc) for adaptive dose escalation in HNSCC patients with highly resistant tumor sub-regions identified using FDG-PET images. Material/Methods: Serial FDG-PET images acquired during chemoradiotherapy from five HNSCC patients were used to assess intra tumoral dose-response distributions. For each patient, a hybrid treatment scheme was employed: a uniform target dose of 2Gy per fraction to be delivered for the first 20 fractions. For the remaining 15 fractions, an adaptive hypofractionated treatment targeted the local resistant sub-regions using a desired non-uniform dose distribution determined by individual tumor metabolic activity and early treatment response. 1 Three treatment planning techniques were evaluated: 1) volumetric modulated arc therapy (VMAT); 2) 4-field IMPT; and 3) SPArc optimized by iteratively resampling control points and energy-layers using a published method. 2 The same target and organ at risk (OAR) objectives were applied during optimization for all techniques. Results: Each patient had 1-2 of isolated resistant sub-regions (0.9-3.2cc) requiring a high fractional dose of 3.3-5.3 Gy determined using a pre-constructed dose prescription function. 1 All techniques achieved coverage of the resistant regions, with a median planned dose (ranging) of 103.1% (97.3-106.2%), 108.6% (102.2-114.5%), and 117.5% (104.3 122.3%) of the desired target dose for VMAT, IMPT, and SPArc, respectively. Figure shows one patient’s treatment plans and dose-volume histograms (DVH)s and the table presents the DVH parameters for all patients across different techniques.

Figure Dose distributions of a patient with highly resistant sub-regions in the tumor center (left) and the corresponding DVH of the 3 plans (right).