ESTRO 2025 - Abstract Book

S3685

Physics - Quality assurance and auditing

ESTRO 2025

with the TPS dose calculation. This work presents the first validation of this novel treatment technique and shows that RAD plans can be accurately delivered by a Truebeam linac system. This commissioning allows us to safely implement RAD for future breast cancer patients.

Keywords: RapidArc Dynamic, hybrid planning

References: 1 Micke A, Lewis DF, Yu X. Multichannel film dosimetry with nonuniformity correction. Medical physics . 2011;5:2523– 2534;doi:10.1118/1.3576105 2 Crijns W, Maes F, van der Heide UA, van den Heuvel F. Calibrating page sized Gafchromic EBT3 films. Medical physics . 2013;1:012102;doi:10.1118/1.4771960

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Digital Poster Gating latencies of the ExacTrac Dynamic system installed at an Elekta linac Catrin Rodenberg 1 , Christopher Kurz 1 , Vanessa da Silva Mendes 1 , Stefanie Corradini 1 , Claus Belka 1,2,3 , Guillaume Landry 1 , Michael Reiner 1 1 Department of Radiation Oncology, LMU University Hospital, LMU Munich, Munich, Germany. 2 Bavarian Cancer Research Center, (BZKF), Munich, Germany. 3 German Cancer Consortium (DKTK), partner site Munich, a partnership between DKFZ and LMU University Hospital Munich, Munich, Germany Purpose/Objective: ExacTrac Dynamic (ETD, Brainlab AG, Germany) is an IGRT and surface-guided radiation therapy (SGRT) system, also used for respiratory-gated treatments in deep-inspiration breath-hold (DIBH). The treatment unit’s end-to-end latencies arise from contributions of the linear accelerator (linac) and the gating system. To date, no gating latencies of ETD have been reported. We aim to estimate ETD’s latencies at an Elekta linac. Material/Methods: At a Versa HD linac (Elekta AB, Sweden) with ETD as gating device, we utilized a Bicron BC-412 plastic scintillator (Saint-Gobain, France) to indicate the beam state (on/off). The vertical stage of the CIRS Dynamic Thorax Phantom (SunNuclear, USA) combined with a thermoplastic mask mimicked thoracic surface motion, performing a step function, to determine the lower gating level, and a DIBH pattern of 15 breathing cycles. Inspired by [1], a high frame-rate camera (GoPro Inc., USA) captured surface motion and scintillator state in the treatment room. Additionally, in the control room, at the Elekta “Response control module”, the interface between gating system and linac, a second camera (iPhone, Apple Inc., USA) monitored an LED representing the gating status of the linac. We extracted surface position, scintillator, and LED state from each video frame. By filming a digital stopwatch, we assessed the videos’ frame rates and synchronized the signals at a post-processing stage. Beam-on/off latencies, the delays between gating window entry/exit and beam on/off, were analysed for each breathing cycle. The time lag between the surface entering/exiting the gating window and the LED switching on/off gives an upper limit of ETD’s contribution. We recorded three videos each on two separate days, spaced four months apart.