ESTRO 2025 - Abstract Book

S2825

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

ESTRO 2025

ESTRO: Challenges in Re-Irradiation: from Art to Science: Monthly Webinars – Oct 2023 to May 2024 https://www.estro.org/Workshops/Challenges-in-Reirradiation-From-Art-to-Science Irish Association of Physicists in Medicine (IAPM) https://iapm.ie/ NCRI 2019. “Cancer Incidence Projections for Ireland 2020-2045”, National Cancer Registry Ireland (2019).

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Poster Discussion Simultaneous optimization of beam orientations and cumulative EQD2 distribution for reirradiation of patients with lung cancer Nathan Torelli 1 , Jonas Willmann 1,2 , Madalyne Day 1 , Nicolaus Andratschke 1 , Jan Unkelbach 1 1 Department of Radiation Oncology, University Hospital Zurich and University of Zurich, Zurich, Switzerland. 2 Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, USA Purpose/Objective: Treatment planning for reirradiation is challenging as the dose delivered in the prior radiotherapy needs to be considered for proper risk assessment [1]. In this study, we developed a beam orientation optimization algorithm for reirradiation planning and investigated whether the selection of favorable non-coplanar beam orientations may reduce the doses to thoracic organs-at-risk (OARs) in patients with locoregionally recurrent non-small cell lung cancer (NSCLC). Material/Methods: Fifteen cases of challenging high-dose reirradiation for locoregionally recurrent NSCLC treated at our institution were included in this in-silico study. For each patient, the dose distribution from the initial treatment was first mapped to the reirradiation planning CT scan, using rigid dose registration, and subsequently converted to equivalent dose in 2 Gy (EQD2). A 2-arc non-coplanar reirradiation plan, combining dynamic gantry and couch rotation, was then generated using a novel EQD2-based direct aperture optimization (DAO) algorithm, which allows for the simultaneous optimization of the dynamic gantry-couch path and the cumulative EQD2 distribution of both the original and reirradiation plans (Figure 1). The non-coplanar reirradiation plans were benchmarked against 2-arc coplanar VMAT plans. Coplanar VMAT plans mimic current state-of-the-art practice for reirradiation of NSCLC patients and have been obtained using the same DAO algorithm, but fixing the beam orientations a priori.