ESTRO 2025 - Abstract Book

S2813

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

Conclusion: When considering all OARs, the dosimetric benefit of VMAT over 3D-CRT depends on the patient size and VMAT beam arrangement. VMAT induced higher secondary cancer risk than 3D-CRT and the risk increased for taller patients. Short patients benefitted most of VMAT and VMAT with posterior spinal arcs spared the OARs best. Results of the study may not be generalized for obese patients.

Keywords: Craniospinal irradiation techniques, Patient size

References: [1] Schneider U, Sumila M, Robotka J. Site-specific dose-response relationships for cancer induction from the combined Japanese A-bomb and Hodgkin cohorts for doses relevant to radiotherapy. Theor Biol Med Model. 2011 Jul 26;8:27. doi: 10.1186/1742-4682-8-27 [2] UNSCEAR. Report to the General Assembly: Sources and effects of ionizing radiation. Annex I – Epidemiological evaluation of radiation-induced cancer. 2000. 2390 Digital Poster Optimising Breast Cancer Radiotherapy: Feasibility Study of VMAT with Nodal Irradiation under Free Breathing Conditions. Angus Main 1 , Ryan Fullarton 1 , Anna M Kirby 2,3 , Alex Dunlop 1 1 The Joint Department of Physics., The Institute of Cancer Research and The Royal Marsden Hospital., London, United Kingdom. 2 Department of Academic Radiotherapy, The Royal Marsden NHS Foundation Trust, London, United Kingdom. 3 Department of Academic Radiotherapy, Institute of Cancer Research, Sutton, United Kingdom Purpose/Objective: For breast cancer patients at higher risk of locoregional recurrence, the internal mammary chain (IMC) is recommended to be included for radiotherapy 1 . In such patients, breath-hold is often recommended to spare heart and lung dose but not all patients can tolerate breath-hold. Given concerns around robustness of VMAT interplay with breathing motion 2 , patients who cannot tolerate breath-hold are treated with wide-tangents (WTs) at our centre. However, WTs often deliver inferior target coverage than VMAT to the nodes 3 . This study retrospectively simulates free breathing in VMAT and WT plans, to compare degradation of plan quality associated with breathing motion to establish whether patients who cannot tolerate breath-hold could be treated with VMAT. Material/Methods: Ten patients (5 left, 5 right) previously treated for breast cancer that received a CT in free breathing were selected. Using RayStation v2023B (RaySearch Laboratories, Stockholm, Sweden), WT and VMAT plans were created (40 Gy in 15 fractions). Breathing motion was simulated by subdividing the beam into sections and shifting isocentres