ESTRO 2025 - Abstract Book

S3875

Radiobiology - Immuno-radiobiology

ESTRO 2025

Material/Methods: In vivo experiments were conducted by injecting two million GL261 cells into the left flank of C57BL/6 mice. The mice were divided into the following groups: 10 received single-fraction conventional radiation therapy (CONV) at doses of 10 Gy, 15 Gy, or 25 Gy; 10 received mean doses of 25 Gy or 30 Gy using single-fraction microbeam radiation therapy (MBRT); and ten mice served as an untreated control group. To assess the significance of the valley dose, a combination therapy group of 10 mice received 25 Gy MBRT immediately followed by 5 Gy conventional RT. Tumor volume was measured with a caliper. Survival curves and skin damage were monitored for up to 90 days post treatment. MBRT was delivered using an in-house custom collimator and installed on a small animal irradiator (SmART, PXI) at the preclinical imaging facility[3]. Results: Tumor volume measurements revealed complete tumor control in the CONV (25 Gy) group and effective tumor suppression in the MBRT groups compared to the control, lasting up to 21 days post-treatment. Survival curves showed a similar (not statistically different) survivor percentage for the MBRT and CONV groups (Figure 1a). No acute radiation damages were found for the MBRT groups, except for one mouse belonging to the MB 30Gy group, while the CONV group mice showed severe damage when treated with 15 and 25 Gy (Figure 1b). Preliminary results on combination treatment showed a complete tumor control for the MBRT-CONV group compared with the MBRT 21 days after the treatment (Figure 2).

Conclusion: These preliminary findings set the stage for further exploration of the biological mechanisms underlying MBRT efficacy and the potential involvement of the immune system. MBRT-CONV efficacy will be tested on an orthotopic glioblastoma model.

Keywords: mini beam radiotherapy, immune response

References: [1] A. Bertho et al. , “Evaluation of the Role of the Immune System Response After Minibeam Radiation Therapy,” Int J Radiat Oncol Biol Phys , vol. 115, no. 2, 2023, doi: 10.1016/j.ijrobp.2022.08.011. [2] C. Fernandez-Palomo, S. Chang, and Y. Prezado, “Should Peak Dose Be Used to Prescribe Spatially Fractionated Radiation Therapy?—A Review of Preclinical Studies,” 2022. doi: 10.3390/cancers14153625. [3] C. Koksal Akbas et al. , “Preclinical photon minibeam radiotherapy using a custom collimator: Dosimetry characterization and preliminary in-vivo results on a glioma model,” Physica Medica , Jul. 2024.

1669

Proffered Paper CD98hc-dependent amino acid transport as a universal regulator of HNSCC radioresistance and immunity Ayşe Sedef Köseer 1 , Melike Demir 1 , Mareike Gruhn 2 , Jacqueline Nathansen 2 , Dominik Haim 3,4 , Max Kemper 3,5 , Steffen Löck 2,3,6 , Mechthild Krause 2,3,6 , Annett Linge 2,3,6 , Claudia Arndt 7 , Anna Dubrovska 2,3,6 1 Institute of Radiooncology-OncoRay, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Dresden, Germany. 2 OncoRay - National Center for Radiation Research in Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden and Helmholtz-Zentrum Dresden - Rossendorf (HZDR), Dresden,