S1913
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
resolved earlier in the alternating-day group, typically within approximately three months, whereas in the previous schedule they tended to appear later. DVH metrics and OAR doses were comparable between schedules, and no correlations linked the alternating- day schedule to increased toxicity. Conclusion: Current evaluation indicates that alternating-day SBRT delivery on CyberKnife is well tolerated, with no increase in early toxicity and no negative impact on plan quality. Our department will continue applying the alternating-day schedule and will further focus on assessing and optimising OAR constraint limits within this treatment approach. The sample size will be expanded as new data are collected to support ongoing refinement of planning strategies. References: [1] Greco C, Pares O, Pimentel N, Louro V, Nunes B, Kociolek J, et al. Urethra sparing with target motion mitigation in dose-escalated extreme hypofractionated prostate cancer radiotherapy: 7-year results from a phase II study. Front Oncol. 2022;12:863655. doi:10.3389/fonc.2022.863655 Keywords: Toxicity, prostate, CyberKnife Automated Volumetric Modulated Arc Therapy Planning for Lung Cancer: A Dosimetric and Plan Complexity Analysis Johann Brand 1 , Juliane Szkitsak 1 , Rafael Lobao 1 , Bernd Niklas Axer 1,2 , Lucas Pieper 1 , Oliver J. Ott 1 , Marlen Haderlein 1 , Florian Putz 1 , Rainer Fietkau 1 , Stefanie Corradini 1 , Christoph Bert 1 , Stefan Speer 1 1 Department of Radiation Oncology, University Hospital Erlangen, Erlangen, Germany. 2 Innovation Strategy and Technology, Siemens Healthineers AG, Forchheim, Germany Purpose/Objective: Volumetric modulated arc therapy (VMAT) planning for lung tumors is highly complex due to large anatomical variability and the close proximity of organs-at-risk (OARs). Manual planning depends on individual Digital Poster 3009 experience and can therefore lead to inconsistencies in plan quality. This study evaluates the University Hospital Erlangen–Automated Treatment Planning (UKER-ATP) software [1], implemented in RayStation 12A (RaySearch, Stockholm, Sweden), by comparing automatically generated plans (APs) with manually created clinical plans (MPs). The analysis focuses on differences in dose distribution and plan complexity. Material/Methods: Thirty lung cancer patients treated with manually optimized VMAT plans were retrospectively replanned using UKER-ATP [1]. The software combines scripted
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Impact of alternating-day fractionation on treatment outcome and toxicity in CyberKnife prostate SBRT Michaela Jindráková 1 , Tomá š Ko ř ínek 2 , Tomá š Veselsk ý 1 , Ferdinand T ř ebick ý 1 1 Institute of Radiation Therapy, The Military University Hospital Prague, Prague, Czech Republic. 2 Medical Exposure Department, National Radiation Protection Institute, Prague, Czech Republic Purpose/Objective: The purpose of this study was to assess whether an alternating-day treatment schedule influences clinically monitored toxicities and treatment outcomes in prostate cancer patients treated with stereotactic body radiotherapy (SBRT) on the CyberKnife system compared with a consecutive-day schedule. This evaluation was initiated due to urogenital toxicities reported by physicians prior to the formal toxicity questionnaire follow-up. In response to these observations, the maximum dose constraint for urethra was reduced from 45 Gy [1] to 38 Gy and the alternating-day schedule was introduced. Because these changes affected treatment planning, the study also aimed to investigate whether the modified schedule and revised constraints led to measurable differences in dosimetric plan parameters. Material/Methods: Thirty patients with localised prostate cancer treated between late 2023 and mid-2024 were analysed. All patients received SBRT in a fractionation scheme of 7.5 Gy delivered in 5 fractions. Before each fraction, patients underwent a CT scan followed by offline adaptive radiotherapy evaluation. Tracking was performed using four fiducial markers, and if organ-at- risk (OAR) or target constraints were not met, a replan was performed. Patients were assigned to one of two treatment schedules: (1) standard delivery of five fractions on consecutive days or (2) delivery with a one-day break between fractions.Three datasets were used for evaluation: plan parameters exported from the treatment planning system, dose-volume- histogram (DVH) metrics for targets and OAR, and toxicity data collected through questionnaires before treatment, after treatment, and at 3-week, 3-month and 6-month follow-ups. A Python-based analysis workflow integrated all datasets and performed descriptive statistics as well as correlation analyses between treatment schedule, dosimetric plan parameters and toxicity outcomes. Results: Based on the currently available dataset, no significant increase in acute or early late urogenital toxicities was observed in the alternating-day group compared with the standard consecutive-day schedule. Dysuria
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