S1906
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
United Kingdom. 4 Development, RaySearch Laboratories, Stockholm, Sweden. 5 Oncology, Leeds Cancer Centre, Leeds, United Kingdom. 6 Division of Cancer Sciences, The University of Manchester, Manchester, United Kingdom. 7 School of Medicine, University of Leeds, Leeds, United Kingdom Purpose/Objective: Reirradiation (reRT) treatment planning must account for doses delivered during previous treatment courses, adding complexity to the process. The absence of a standardized methodology leads to significant inter-centre variation in planning practices, which may affect patient outcomes. This study of plan consistency between centres evaluates a novel treatment planning system functionality that enables plan optimization based on the full cumulative equieffective dose in 2 Gy fractions (EQD2) [1]. Material/Methods: Four lung cancer reRT cases, each including prior and reRT CT datasets and structure sets, were shared among three UK centres. Contouring and deformable image registration between treatment courses were centrally performed and verified before data distribution. Consensus EQD2-based dose constraints for optimization were established. Each centre independently generated reRT plans using the EQD2 optimization module [2] (RayStation v2025ReRT, RaySearch Laboratories, Stockholm). The EQD2 optimization tools enabled optimization directly against cumulative dose constraints. Plans received clinical review as part of the plan selection process. Dose statistics from EQD2-optimized plans were extracted for each organ of interest and PTV.
respectively.
Conclusion: The updated ASF (v18.1 MR1) has improved from v18.1. The plans optimized with the balanced setting provided higher median CTVskin and PTVskin coverages and Dskin compared to VB. References: [1] Nykänen T, Raatikainen V, Kärnä A, Koivumäki T. Performance evaluation of a new automated skin flash method for radiotherapy of breast cancer. Phys Imaging Radiat Oncol 2025;35. https://doi.org/10.1016/j.phro.2025.100810.[2] Nicolini G, Fogliata A, Clivio A, Vanetti E, Cozzi L. Planning strategies in volumetric modulated arc therapy for breast. Med Phys 2011;38:4025–31. https://doi.org/10.1118/1.3598442. Keywords: Breast cancer, Skin flash, VMAT Proffered Paper 2891 EQD2-optimised reirradiation plan consistency in a multi-centre study Christopher Thompson 1 , Aleksandra Zyryanova 1 , Liam Walker 2 , Thomas Davies 3 , Nick Willis 2 , Stina Svensson 4 , Jakob Ödén 4 , Rasmus Bokrantz 4 , Lars Glimelius 4 , Kjell Eriksson 4 , John Lilley 1 , Louise Murray 5 , Nick West 2 , Eliana V Osorio 6 , Ane Appelt 7 1 Medical Physics, Leeds Cancer Centre, Leeds, United Kingdom. 2 Medical Physics, THE NEWCASTLE UPON TYNE HOSPITALS NHS FOUNDATION TRUST, Newcastle, United Kingdom. 3 Medical Physics, THE CHRISTIE NHS FOUNDATION TRUST, Manchester,
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