ESTRO 2025 - Abstract Book

S3343

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2025

4129

Digital Poster Time-resolved and multi-point dose measurements in a novel deformable and MRI-compatible beating heart phantom Manon M.N Aubert 1 , Prescilla Uijtewaal 1 , Yoan LeChasseur 2 , Kalin Penev 3 , Laurie J.M de Vries 1,2 , Nick Hartman 3 , Niusha Kheirkhah 3 , Benjamin Coté 2 , François Therriault-Proulx 2 , Stephanie Smith 3 , Madelon van den Dobbelsteen 1 , Pim T.S Borman 1 , Stefano Mandija 1,4 , Astrid L.H.M.W Van Lier 1 , Martin F Fast 1 1 Radiotherapy, UMC Utrecht, Utrecht, Netherlands. 2 _, Medscint, Quebec City, Canada. 3 _, IBA QUASAR, London, Ontario, Canada. 4 Computational Imaging Group for MR Diagnostics & Therapy, UMC Utrecht, Utrect, Netherlands Purpose/Objective: Stereotactic radiotherapy has emerged as salvage treatment for patients with ventricular tachycardia and the MR linac offers MRI-based guidance during such treatments [1]. In this context, the development of a deformable and MRI-compatible beating heart phantom, offering time-resolved and multi-point dose measurements, is key for workflow development, quality assurance, and end-to-end testing. This study presents a novel heart phantom with integrated real-time dosimeters and demonstrates its capabilities for an MR-linac gating treatment.

Material/Methods:

The phantom (IBA QUASAR, London-ON, Canada) consists of a realistic silicon heart model (length≈6cm, width≈8cm, thickness≈6cm) with two ventricles filled with contrast solution (4ppm-Mn 2+ ). Four Hyperscint HS-RP200 plastic scintillation detectors (PSDs) (Medscint, Quebec QC, Canada) [2] were integrated in the silicon. The phantom was connected to the motor of the QUASAR MRI 4D Motion Phantom via a piston mechanism which displaces the contrast solution and thus deforms the heart model [Fig1a]. A treatment plan was created for the 1.5 T Unity MR-linac (Elekta AB, Stockholm, Sweden) containing two squared (3x3cm 2 ) beams of 1000MU. Beam 1 was delivered at gantry 322° reaching PSDs 3-4 and beam 2 at gantry 110° reaching PSDs 1-2. Treatment planning, adaptation and static delivery were performed at the mid-position of the waveform [Fig1b-c]. For the dynamic cases, a sinusoidal waveform was applied to the piston (frequency=60bpm, amplitude=10mm). To mitigate the motion, we used the MR-linac’s clinical gating approach (cine-MRI based, 6Hz). Additionally, we acquired static 3D-bFFE scans (resolution=1x1x1mm 3 ) at extreme positions of the waveform to estimate the PSD displacement.