S1907
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
Results:
optimization provides a reproducible, clinically meaningful framework for reRT plan generation. References: [1] Ödén J, Eriksson K, Svensson S, Lilley J, Thompson C, Pagett C, Appelt A, Murray L, Bokrantz B. Technical note: Optimization functions for re-irradiation treatment planning. Med Phys. 2024; 51: 476–484. https://doi.org/10.1002/mp.16815[2] Murray L, Thompson C, Pagett C, Lilley J, Al-Qaisieh B, Svensson S, Eriksson K, Nix M, Aldred M, Aspin L, Gregory S, Appelt A. Treatment plan optimisation for reirradiation. Radiother Oncol. 2023 May;182:109545. doi: 10.1016/j.radonc.2023.109545 Keywords: Reirradition, EQD2, Treatment Planning Digital Poster 2942 Optimization of beam on time and organs-of- interest dose characteristics of RapidArc Dynamic plans for breast cancer Topi Nykänen 1,2 , Ville Raatikainen 1 , Aarno Kärnä 1 , Katariina Näkki 1 , Tuomas Koivumäki 1 1 Department of Medical physics, Hospital Nova of Central Finland, Wellbeing Services County of Central Finland, Jyväskylä, Finland. 2 Department of Physics, University of Jyväskylä, Jyväskylä, Finland Purpose/Objective: The aim of this study was to determine the optimal arc and static angle modulated port (STAMP) configuration for whole breast irradiation with RapidArc Dynamic, RAD, (Varian Medical Systems, USA) to find an optimal solution for treatment efficiency while keeping high planning target volume (PTV) coverage and minimizing organs-of-interest doses. Material/Methods: This study evaluated the beam on time and organ-at- risk doses for 10 whole breast patients utilizing 12 different RAD setups in comparison to conventional VMAT plans. All VMAT plans used a four split arc setup [1,2] and RAD plans utilized two or three arcs with a total of three to six tangentially positioned STAMPs. The plans were optimized with ‘balanced’, ‘static’ or ‘static dominant’ setting. PTV V95% coverage of at least 95 % was required in all plans. All plans were optimized for a TrueBeam linear accelerator with a Millenium 120 MLC and used a beam energy of 6 MV. Gantry rotation speed was set to 4.8 deg/s. The optimizations were done in Eclipse v18.1 using Photon Optimizer v18.1 and AcurosXB v18.1. Wilcoxon signed- ranked test was used to test statistical significance in IBM SPSS (IBM, USA). Results: In most of the studied plan setups, RAD lowered beam on times compared to VMAT despite an increase in MUs (Table 1). The shortest median beam on time of
Figure 1 shows inter-patient variability and plan consistency across centres. All centres met predefined EQD2 cumulative constraints for organs of interest (oesophagus pericardium, airways, brachial plexus and spinal canal). Figure 1 demonstrates that EQD2- optimized plans produce consistent OAR sparing across centres, while PTV coverage (physical dose) remains broadly maintained. Variability between patients can be easily assessed, providing a visual benchmark for plan reproducibility. The most limiting organ of interest was the pericardium where doses were close to the clinical goal. In this case close grouping between the centres can be observed, suggesting good convergence in plans between centres. There was one plan for centre B with relatively low PTV coverage, this is correlated with a lower trachea and proximal bronchial tree dose. For centre B, it was decided to considerably reduce doses below the mandatory constraint after clinical review, which contributed to plan variability. Conclusion: This study evaluated the performance and inter-centre consistency of full EQD2-based reirradiation (reRT) optimization within a clinical treatment planning system. Assessment of patient-specific dose distributions demonstrated consistent organ of interest sparing across centres, although some small inter centre variations remained. Overall, EQD2-based
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