ESTRO 2025 - Abstract Book

S2836

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

2815

Digital Poster Dose comparison of definitive radiotherapy between modalities for head and neck cancer – a single institution’s experience Brandon Reber, Jing Qian, Daniel Ebner, Scott Lester, Daniel Ma, Michelle Neben, David Routman, Jessica Wilson, Satomi Shiraishi Radiation Oncology, Mayo Clinic, Rochester, USA Purpose/Objective: The choice of radiation modality directly influences dose distribution which can significantly impact tumor control and toxicity outcomes in head and neck cancer (HNC). Proton therapy has dosimetric advantages compared to photon therapy. Debate remains about the clinical reduction in toxicity across modalities, though recent phase 3 randomized data reported reduced malnutrition and gastrostomy tube dependence for proton therapy compared to photon therapy(1). Part of the toxicity heterogeneity reported across studies may be in part secondary to end of range and proton biological dose effects. We sought to examine dosimetric differences between proton and photon therapy for patients undergoing definitive radiotherapy for HNC. Material/Methods: 105 HNC patients treated with definitive proton therapy and 56 HNC patients treated with definitive photon therapy at our institution from 2013-2024 were retrospectively identified. The clinically delivered treatment plans were optimized using Eclipse, and Monte Carlo (MC) was used to determine the proton biological dose. The max dose (D 0.1% ) was collected for the brain stem, spinal cord, mandible, and brachial plexus. The mean dose was collected for the parotids, larynx, esophagus, cochlea, oral cavity, and submandibular glands. Mann-Whitney U tests were used to determine if significant differences exist in the delivered dose to organs at risk (OARs) between the cohorts. Significance was determined if p<0.05, using the Hold method for multiple comparisons. A median cumulative DVH curve was constructed for each OAR. Results: As shown in Figure 1, proton therapy demonstrated statistically better physical dose sparing for most OARs investigated in this study, with the cochlea being the exception. Although the physical dose coverage for proton and photon therapies is similar across different clinical target volumes (ctvs), the model-based biological dose shows a substantial escalation which may influence tumor control rates. All OARs except the cochlea and submandibular glands received significantly different photon dose compared to proton biological dose. The median cumulative DVH for the OARs in both proton and photon treatments are presented in Figure 2.