ESTRO 2025 - Abstract Book

S2724

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

ESTRO 2025

Conclusion: In this study, RO-DYMBARC offers superior dosimetric plan quality with similar robustness to DIBH variations compared to conventional PTV-based and RO-VMAT for left-sided breast radiotherapy. RO-VMAT also shows superior dosimetric plan quality compared to conventional VMAT plans; however, DYMBARC plans further enhance OAR sparing, highlighting the advantages of mixed-beam radiotherapy. Supported by the Stiftung für Klinisch-Experimentelle Tumorforschung and Varian, a Siemens Healthineers Company.

Keywords: Robustness, Mixed-Beam, DIBH

References: 1. Zhu C et al. Dosimetric optimization for dynamic mixed beam arc therapy (DYMBARC). Med Phys . 2024; doi.org/10.1002/mp.17467 2. Segars WP et al. 4D XCAT phantom for multimodality imaging research. Med Phys . 2010; doi.org/10.1118/1.3480985 3. Modat M et al. Fast free-form deformation using graphics processing units. Comput Methods Programs Biomed . 2010; doi.org/10.1016/j.cmpb.2009.09.002 4. Zobrist B et al. Monte Carlo dose calculation for photon and electron radiotherapy on dynamically deforming anatomy. Med Phys . 2024; doi.org/10.1002/mp.17472 5. Hurkmans C et al. Harmonization of breast cancer radiotherapy treatment planning in the Netherlands. Tech Innov Patient Support Radiat Oncol . 2021; doi:10.1016/j.tipsro.2021.06.004

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Digital Poster Evaluating the dosimetric performance of 6 MV FFF beams in left-sided breast VMAT Kaj Bayley, Eujin Chan, Elizabeth Patterson, Brindha Subramanian Radiation Oncology, GenesisCare, Melbourne, Australia

Purpose/Objective: Flattening filter-free (FFF) beams are used in stereotactic treatments due to their higher dose rates, bell-shaped profiles, and reduced head scatter, resulting in lower peripheral radiation doses than flattened beams [1]. This study evaluated Varian TrueBeam 6MV FFF beams for non-stereotactic volumetric modulated arc therapy (VMAT) of left sided breast cancer. Dosimetric plan quality was assessed by comparing Planning Target Volume (PTV) dose coverage and doses to Organs At Risk (OARs), specifically the ipsilateral lung and heart, between flattened and FFF 6 MV beam plans created in Eclipse™ v16.1 (Varian Medical Systems). Plan deliverability was verified with patient-specific quality assurance using ArcCHECK™ (Sun Nuclear) measurements and RadCalc 3D (LAP, Germany) calculations. Material/Methods: In this retrospective study, ten left-sided breast VMAT patients were selected, each consisting of four ipsilateral VMAT fields covering 150°. A prescription of 40.05 Gy delivered over 15 fractions was used for all patients. An experienced breast planner replanned the cases using FFF beams, optimizing the plans with a newly validated RapidPlan model specific to breast and FFF treatments. The plans were calculated with the Acuros XB beam model (2.5mm grid size) and compared to flattened beam plans in terms of clinical goal performance and monitor units (MU).