S1751
Physics - Dose prediction/calculation, optimisation and applications for particle therapy planning
ESTRO 2026
CTV66 and Dmean/D0.03cc for organs at risk (OARs) were extracted. Statistical significance was tested using the Wilcoxon signed-rank test (p<0.05 significant). NTCP for xerostomia and dysphagia was estimated using published models [1]. Results: Figure 1 shows nominal dose distributions for the six planning strategies in a representative patient.
bath exposure compared with VMAT, which may translate clinically into lower rates of haematologic toxicity. Further work incorporating published BM dose-constraint optimisation is warranted. References: [1] Cancer Research UK (2025) Cervical cancer statistics. Available at: https://www.cancerresearchuk.org/health- professional/cancer-statistics/statistics-by-cancer- type/cervical-cancer#Cervicalcs0 (Accessed: 6 November 2025).[2] Hara JHL, Jutzy JMS, Arya R, Kothari R, McCall AR, Howard AR, Hasan Y, Cursio JF, Son CH. Predictors of Acute Hematologic Toxicity in Women Receiving Extended-Field Chemoradiation for Cervical Cancer: Do Known Pelvic Radiation Bone Marrow Constraints Apply? Adv Radiat Oncol. 2022 Jun 13;7(6):100998. doi: 10.1016/j.adro.2022.100998. PMID: 36420189; PMCID: PMC9677190 Keywords: PBT, Cervical Cancer proton benefit loss after three weeks of head-and- neck radiotherapy despite robust optimization Monica Bianchi 1,2 , Pasqualina Gallo 2 , Marco Pelizzoli 2 , Laura Breschi 2 , Andrea Bresolin 2 , Francesco La Fauci 2 , Nicola Lambri 1,2 , Francesca Lobefalo 2 , Giacomo Reggiori 2 , Stefano Tomatis 2 , Ciro Franzese 2,3 , Marta Scorsetti 2,3 , Cristina Lenardi 1,4 , Pietro Mancosu 2,3 1 Department of Physics “Aldo Pontremoli”, University of Milan, Milan, Italy. 2 Radiotherapy and Radiosurgery Department, IRCCS Humanitas Research Hospital, Milan, Italy. 3 Department of Biomedical Sciences, Humanitas University, Milan, Italy. 4 Milano Division, National Institute for Nuclear Physics, Milan, Italy Digital Poster Highlight 3171 Purpose/Objective: Anatomical changes during head-and-neck (HN) radiotherapy may degrade the dosimetric quality of proton therapy (PT) plans and compromise model- based patient selection [1]. Robust optimization (RobOpt) aims to limit this sensitivity but is mainly tuned for setup and range uncertainties. This study quantified the dosimetric impact of mid-treatment anatomical changes on photon and proton plans and assessed whether RobOpt can preserve the initial PT benefit after three weeks of treatment. Material/Methods: Eight HN cancer patients were randomly selected from a prospective trial (NCT05081531). Six plans per patient were generated in RayStation v2024A using VMAT and IMPT with three strategies: (i) PTV-based optimization (3 mm margin); (ii) RobOpt with 3 mm/3% setup-range uncertainty; (iii) RobOpt with 5 mm/3%. Dose distributions were recalculated on week-3 CTs and compared to planning CTs. D95% for CTV54 and
At baseline, PT generally achieved higher CTV coverage and lower OAR doses than VMAT. After three weeks, CTV54 D95% decreased by a median of 3±4 Gy for 3 mm/3% IMPT (p=0.01) versus 1±3 Gy for PTV-based VMAT (p=0.04). For CTV66, losses were slightly smaller (IMPT -3±5 Gy, p=0.01; VMAT 0±2 Gy, p=0.25). OAR dose increases were larger for protons: spinal cord D0.03cc +2±9 Gy (p=0.55) and oral cavity Dmean +3±5 Gy (p=0.02); photon variations were ≤ 1 Gy and non- significant. NTCP analysis confirmed a biological reduction of PT benefit: mean dysphagia risk difference (PTV-based VMAT - 3 mm/3% IMPT) fell from 2%±3% (p=0.01) to 1%±4% (p=0.15); xerostomia risk differences remained around 1% and non-significant. Table 1 illustrates dose-volume and NTCP changes across all planning strategies.
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