ESTRO 2025 - Abstract Book

S2407

Interdisciplinary – Other

ESTRO 2025

4061

Digital Poster First in-vivo studies at a compact minibeam and microbeam radiotherapy source Johanna Winter 1,2,3 , Christian Petrich 1,4,3 , Anton Dimroth 1,3,5 , Thomas Beiser 6,7 , Jessica Stolz 1,2 , Jan J. Wilkens 1,4 , Stephanie E. Combs 1,2 , Kurt Aulenbacher 6,7,8 , Thomas E. Schmid 1,2 , Stefan Bartzsch 1,2,3 1 Department of Radiation Oncology, Technical University of Munich, School of Medicine and Health and Klinikum rechts der Isar, Munich, Germany. 2 Institute of Radiation Medicine, Helmholtz Zentrum München GmbH, German Research Center for Environmental Health, Neuherberg, Germany. 3 Research Neutron Source, Heinz Maier-Leibnitz Zentrum (MLZ), Garching, Germany. 4 TUM School of Natural Sciences, Technical University of Munich, Munich, Germany. 5 Central Institute for Engineering, Electronics and Analytics (ZEA), Forschungszentrum Jülich GmbH, Jülich, Germany. 6 Accelerator Design and Integrated Detectors, Helmholtz-Institute Mainz, Mainz, Germany. 7 GSI, Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany. 8 Institute for Nuclear Physics, Johannes Gutenberg University, Mainz, Germany Purpose/Objective Microbeam and minibeam radiotherapy may improve cancer treatment with better tumor control and higher tolerances of normal tissue than conventional radiotherapy. The lack of clinically useable minibeam and microbeam x-ray machines limits clinical translation. Compact x-ray tube-based systems suffer from low dose rates and decreasing peak-to-valley dose ratios (PVDR) with distance from the multislit collimator. Material/Methods We installed and commissioned a line-focus x-ray tube, featuring a strongly eccentric focal spot with a width in the micrometer regime. The electron beam can be controlled by a Pierce electrode up to 300 mA and 300 keV. Open field dose rates were measured close to the beam exit window with a Farmer ionization chamber. Tungsten minibeam and microbeam collimators were fabricated with 40 µm- to 200 μm-wide slits. Radiochromic EBT3 film dosimetry was used to acquire dose profiles. First in-vivo studies with brain tumors in mice were performed with whole brain irradiations of homogeneous doses and minibeams. Results We created an open field dose rate above 7 Gy/s, while vacuum requirements currently limit operation to 30 mA and150 kV. Penumbras of microbeam and minibeam dose profiles remained narrow even at several 10 cm distance from the collimator. Film dosimetry of minibeams (200 μm width, 800 μm spacing) showed a PVDR of 30 in 5 mm PMMA depth for a field size of 20 mm. The mouse brain received 15 Gy homogeneous dose and equivalent uniform dose, respectively, at 5 mm depth with a field size of 10 mm and a beam filtering of 0.5 mm aluminum. Conclusion This is the first compact irradiator achieving microbeam and minibeam qualities that could be clinically used with FLASH dose rates. For increased source performance, we need to solve current problems with the rotating anode bearing, a decreasing beam current during operation and vacuum limits of the cathode.