ESTRO 2024 - Abstract Book

S4642

Physics - Optimisation, algorithms and applications for ion beam treatment planning

ESTR0 2024

1581

Digital Poster

IGRT workflow for pre-clinical proton research and MRI-based response assessment in mouse brain

Barbara Knäusl 1,2 , Stocchiero Silvia 3,1 , Lorenz Langgartner 1 , Esau Poblador Rodríguez 3 , Vanessa Fröhlich 3 , Isselmou Abdarahmane 3,1 , Sabine Leitner 3 , Petra Gröger 3 , Markus Zeilinger 3,2 , Dietmar Georg 1,2 1 Medical University of Vienna, Department of Radiation Oncology, Vienna, Austria. 2 MedAustron, Medical Physics, Wiener Neustadt, Austria. 3 University of Applied Sciences, Competence Center for Preclinical Imaging and Biomedical Engineering, Wiener Neustadt, Austria

Purpose/Objective:

Particle therapy (PT) offers favourable physical depth dose distribution, combined with higher biological effectiveness which is in turn linked to the higher linear energy transfer (LET), especially in the Bragg peak region. Yet, there is a fundamental lack in the understanding of dose and LET effects at the tissue level, at the tumour as well as in organs at risk. In contrast to X-ray-based pre-clinical research with dedicated commercial tools, for PT in-house developments need to be pursued in the first place to enable a high-precision image-guided irradiation workflow. This study reports on developments to set up such a pre-clinical PT framework, covering all aspects from animal handling, imaging, dose prediction including LET determination, high-precision dose delivery, to response assessment. In addition, the potential of an ultra-high field (UHF) strength magnetic resonance imaging (MRI) for response assessment was explored. Finally, the workflow was assessed with the normal tissue model mouse brain. For the high-precision small-volume irradiation, an in-house designed passive beam modifier was combined with a 30 mm PMMA range shifter to achieve shallow depths with a collimation diameter of 5mm. A dedicated proton beam model was created in the treatment planning system RayStation 2023-DTK (v14.0.110.0), offering a high resolution for dose calculation, structure delineation and aperture definition 1 . The dose grid size was adapted to the resolution of the spiral cone-beam µCT (Molecubes, Belgium, 0.225 mAs, 50 kV) with a slice thickness of 0.2 mm, for which a specific Hounsfield unit calibration curve was established. For dose calculation, a Monte Carlo dose engine (v5.5) was used. Treatment plans for half-brain irradiations were created on µCT images. The target volume was created by intersecting the right brain hemisphere with a cylinder of 3 mm diameter (centred around the hippocampus) and successively removing 1 mm at the distal (left) end of the intersection. Treatment plans were optimised concerning target coverage and sparing of the contralateral hemisphere and evaluated by means of dose and dose averaged LET (LET d ) values in the target region and maximal dose and LET d statistics in the left hemisphere averaged over all mice. Material/Methods: