S2507
Radiobiology - Biology of novel irradiation techniques
ESTRO 2026
reduced the rate of tibial malformation (1/13 vs. 8/15), and better maintained trabecular micro-structure. A similar protective trend was observed at 40 Gy. Notably, at 60 Gy, FLASH-RT virtually prevented fractures (1/8 vs. 9/9) despite showing comparable growth suppression. Histology confirmed that compared to CONV-RT, FLASH-RT more effectively mitigated the radiation induced skeletal injury, including growth plate disorganization, impaired ossification, and marrow adiposity. The intraosseous vasculature was also better preserved with FLASH-RT.
expected to use doses below the current EUD, potentially further reducing normal tissue risk while preserving therapeutic efficacy. References: Petrich C, Winter J, Dimroth A, Stolz J, Beiser T, Dehn M, Frignani J, Combs SE, Schilling F, Natour G, Aulenbacher K, Raulefs S, Schmid TE, Wilkens JJ, Bartzsch S. Commissioning, characterization and first high dose rate irradiations at a compact X-ray tube for microbeam and minibeam radiation therapy. Int J Radiat Oncol Biol Phys. 2025 Oct 22:S0360- 3016(25)06398-9. doi: 10.1016/j.ijrobp.2025.10.012. PMID: 41135710. Keywords: Minibeam radiation therapy, MBRT, in vivo Digital Poster 1540 FLASH Radiotherapy Mitigates Growth Inhibition and Preserves Structural Integrity in Developmental Mice Bone Yunwen Huang 1 , Hui Liu 2 , Panpan Hu 2 , Cheng Zheng 2 , Xiaogang Yuan 2 , Ning Zhao 3 , Yidong Yang 1,2 1 Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China. 2 Department of Engineering and Applied Physics, School of Physical Science, University of Science and Technology of China, Hefei, China. 3 Research and development, Raycision Medical Technology Co. Ltd, Hefei, China Purpose/Objective: The remarkable normal tissue-sparing effect of FLASH radiotherapy (FLASH-RT) positions it as a highly promising cancer treatment modality for pediatric patients. The developing skeleton has high metabolic activity and radiosensitivity, and thus is particularly vulnerable to radiation toxicity. This study aims to determine whether and how FLASH-RT spares the developing bone tissues. Material/Methods: The left tibiae of 6-day-old Balb/c suckling mice were irradiated with a single dose of 20, 40, or 60 Gy via either FLASH-RT (57 Gy/s) or conventional radiotherapy (CONV-RT, 5.2 Gy/min). Ten weeks after irradiation, tibiae were collected for high-resolution micro-CT scanning and histological analysis to quantify developmental deficits and micro-architectural preservation. Vascular integrity was specifically assessed at the 20 Gy dose level by Microfil perfusion at 2 and 4 weeks. Results: Both FLASH-RT and CONV-RT arrested tibia growth in a dose-dependent manner. But, FLASH-RT resulted in significantly less growth inhibition compared to CONV- RT. This preservation was most evident at 20 Gy, where FLASH-RT significantly alleviated growth arrest,
Conclusion: Our findings conclude that FLASH-RT offers a significant advantage over CONV-RT by ensuring the structural and vascular integrity of the developing skeleton. The dramatic effects on fracture prevention, even at high doses, and on intraosseous vasculature preservation support FLASH-RT’s strong potential in minimizing skeletal morbidity for pediatric cancer patients. References: [1] ROCHA F S, LIMIRIO P H J O, ZANETTA-BARBOSA D, et al. The effects of ionizing radiation on the growth plate in rat tibiae [J]. Microsc Res Techniq, 2016, 79(12): 1147-51.[2] VERGINADIS I I, VELALOPOULOU A, KIM M M, et al. FLASH proton reirradiation, with or without hypofractionation, reduces chronic toxicity in the normal murine intestine, skin, and bone [J]. Radiotherapy and Oncology : Journal of the European Society For Therapeutic Radiology and Oncology, 2025, 205: 110744.[3] LI J, CHEN X, REN L, et al. Type H
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