S2184
Physics - Inter-fraction motion management and daily adaptive radiotherapy
ESTRO 2026
and adapted (ADAP) plans for rectum (Dmean), bladder (V30Gy), bowel (D0.03cc), and target volumes (PTVT45/PTVN55 D97%). Per-patient medians across 25 fractions were analysed using the Wilcoxon signed- rank test. Correlations were evaluated using Spearman’s ρ . Total treatment time per fraction and inter-fraction variability (coefficient of variation, CV) was analyzed for workflow performance. Protocol compliance was assessed using institutional constraints. Results: ADAP plans showed significantly lower OAR doses than PROG: rectum 126 [117–137] vs 117 [112–127] cGy (p < 0.0001, ρ = 0.61); bladder 129 [116–139] vs 123 [115–135] cGy (p < 0.0001, ρ = 0.75); bowel D0.03 cc 211 [196–231] vs 217 [204–219] cGy (p < 0.0001, ρ = 0.86). Target coverage remained stable or slightly improved: PTVT_99% increased from 170 [129–178] to 179 [177–181] cGy (p < 0.0001, ρ = 0.16), and PTVN_97% from 173 [168–182] to 179 [177–181] cGy (p < 0.0001, ρ = 0.81). Median treatment time per fraction was 23 min [19–28] with low variability (CV 18 % [15– 20]). Protocol compliance improved for all endpoints, correcting all deviations. Conclusion: Daily oART improved OAR sparing while maintaining target coverage and workflow efficiency, supporting its feasibility and clinical value in cervical cancer. Keywords: Ethos, Adaptativa radiotherapy, Cervical cancer An automated framework for fast adaptive proton therapy triggering without target re-segmentation Hooman Bahrdo, Gabriel Guterres Marmitt, Femke Oosterhof, Pietro Pisciotta, Johannes A Langendijk, Stefan Both Radiation Oncology, University Medical Center Groningen, Groningen, Netherlands Purpose/Objective: Adaptive proton therapy must be value-driven to ensure optimal use of this limitedavailable and costly treatment modality. A fast quantitative method to assess the need for plan adaptation without requiring target re-segmentation is currently lacking. In this work, we developed a patient-specific (PS) deep learning framework to trigger potential adaptation needs in oropharyngeal cancer patients (OCPs) treated with intensity-modulated proton therapy (IMPT). Material/Methods: An in-house developed Dual-CNN model for predicting optimal head-and-neck (HNC) patient treatment position served as the base model [1]. Data from 62 OCPs treated with IMPT were analyzed, each with one Proffered Paper 4453
Conclusion: Despite range uncertainty, 4DDR IMPT plans with adaptation showed similar target dose robustness like non-adapted 4DDR VMAT plans over the treatment course. These findings emphasize the importance of incorporating verification patient specific 4DDR into standard VMAT and IMPT clinical workflows to ensure robust treatment delivery in lung cancer patients treated in free breathing. References: 1.Meijers A, Knopf AC, Crijns APG, et al. Evaluation of interplay and organ motion effects by means of 4D dose reconstruction and accumulation.. Radiother Oncol. 150:268–74 (2020). 2.Meijers A, Jakobi A, Stützer K, et al. Log file-based dose reconstruction and accumulation for 4D adaptive pencil beam scanned proton therapy in a clinical treatment planning system: Implementation and proof-of-concept Med Phys. 46:1140–9 (2019).
Keywords: 4D dose reconstruction, Protons, Photons
Digital Poster 4422 Daily online adaptive radiotherapy with Ethos™ in cervical cancer Irene Císcar 1 , Jennifer Hernández 1 , Vanessa Ortiz 1 , Miguel Martínez 2 , Ana Corbalán 2 , Alberto Espinosa 1 , Virginia Alonso 1 , Pedro Pablo Escolar 1 , Silvia Rodríguez 1 , Vicente Luis García 1 , Alfredo Serna 2 , Juan Salinas 1 1 Radiation Oncology, Complejo Hospitalario Universitario de Cartagena, Cartagena, Spain. 2 Medical Physics and Radiation Protection, Complejo Hospitalario Universitario de Cartagena, Cartagena, Spain Purpose/Objective: To evaluate the dosimetric impact and workflow performance of daily online adaptive radiotherapy (oART) with ETHOS™ in cervical cancer. Material/Methods: Eight patients with locally advanced cervical cancer were treated with oART (25fx × 1.8Gy). Dosimetric parameters were extracted from scheduled (PROG)
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