ESTRO 2025 - Abstract Book

S2722

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

ESTRO 2025

Conclusion: Our study showed an advantage of VMAT compared to 3D-CRT following ESTRO-ACROP consensus for implant sparing in PMRT.

Keywords: Postmastectomy radiation, ESTRO-ACROP guidelines

References: 1. Chang KH, A Retrospective Dosimetric Analysis of the New ESTRO-ACROP Target Volume Delineation Guidelines for Postmastectomy Volumetric Modulated Arc Therapy After Implant-Based Immediate Breast Reconstruction. Front Oncol. 2020 Oct 20;10:578921. doi: 10.3389/fonc.2020.578921. PMID: 33194701; PMCID: PMC7606939. 2. Göksel EO. Dosimetric evaluation of VMAT and helical tomotherapy techniques comparing conventional volumes with clinical target volumes based on new ESTRO ACROP post-mastectomy with immediate implant reconstruction contouring guidelines. Radiat Oncol. 2022 Oct 21;17(1):168. doi: 10.1186/s13014-022-02134-y. PMID: 36271401; PMCID: PMC9587659.

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Digital Poster Robustness Assessment of Robust Optimized Dynamic Mixed-Beam Arc Radiotherapy for Left Breast Treatments Under Deep Inspiration Breath-Hold Variations Björn Zobrist, Werner Volken, Hannes Anton Loebner, Chengchen Zhu, Silvan Mueller, Peter Manser, Michael Karl Fix, Jenny Bertholet Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern, Switzerland Purpose/Objective: Deep inspiration breath-hold (DIBH) for left breast radiotherapy reduces respiratory movement and improves heart sparing. Despite this, delivery uncertainties persist due to variations in DIBH, both between and within individual breath-holds. This study aims to assess and compare the dosimetric plan quality and robustness under DIBH variations of robust optimized (RO) dynamic mixed-beam arc radiotherapy (DYMBARC) 1 and state-of-the-art VMAT. XCAT 2 anthropomorphic phantom and NiftyReg 3 for deformable image registration (DIR). These were designed to depict 12 distinct DIBH variations, incorporating up to 5 mm chest wall displacement from the reference DIBH level. For each phantom, three treatment plans for left breast were created: a PTV-based VMAT plan, a RO-VMAT plan, and a RO-DYMBARC plan, all using the XCAT-generated reference DIBH CT (nominal plans). 42.4 Gy in 16 fractions are prescribed to the target. The RO-VMAT plan was included in the analysis to distinguish the specific advantages that arise from the robust optimization from those that result from the mixed-beam treatment technique. Table 1 lists the details of the three treatment planning techniques. For robustness assessment, the dose was recalculated for all seven cases and 12 DIBH variations using deformable voxel geometry Monte Carlo simulations 4 with known DVFs. For the evaluation, different dosimetric endpoints 5 were compared between the treatment techniques for the nominal plan and all DIBH variations using Wilcoxon matched-pair signed-rank test (α = 5%). Material/Methods: Seven realistic phantoms with known deformation vector fields (DVFs) were generated using the