ESTRO 2025 - Abstract Book

S3929

Radiobiology - Normal tissue radiobiology

ESTRO 2025

Conclusion: This research confirms that the average dose rate is the primary temporal parameter for decreasing side effects following pulsed electron FLASH-RT. A threshold rate of 100 Gy/s was required for maximizing the magnitude of the FLASH effect. Increasing tissue oxygenation diminished the FLASH effect, revealing its dependence on oxygen. The 10-fraction regimen was unsuitable for preserving the FLASH effect in early responding intestine toxicity model. These findings provide a benchmark for FLASH VHEE-RT development.

Keywords: Fractionation, Oxygen, FLASH

2544

Poster Discussion Fractionated FLASH irradiation reduces acute skin toxicity in a murine model. Line Kristensen 1,2,3 , Sky Rohrer 1,3 , Jacob Graversgaard Johansen 1,3 , Lone Hoffmann 3,4 , Lars Hjorth Præstegaard 4 , Per Rugaard Poulsen 1,3 , Brita Singers Sørensen 1,2,3 1 Danish Centre for Particle therapy, Aarhus University Hospital, Aarhus, Denmark. 2 Department of Experimental Clinical Oncology, Aarhus University Hospital, Aarhus, Denmark. 3 Department of Clinical Medicine, Aarhus University, Aarhus, Denmark. 4 Department of Oncology, Aarhus University Hospital, Aarhus, Denmark Purpose/Objective: Several preclinical studies have shown a favourable effect of ultra-high dose rate (UHDR) irradiation for normal tissue-sparing (FLASH). Most of these studies report single-dose irradiations and do not include a fractionated irradiation scheme. As fractionated radiotherapy is the standard for clinical treatments, the interplay between fractionation and FLASH sparing is of high relevance and needs to be investigated. This study quantified the tissue sparing effect of FLASH on acute skin toxicity with a single dose, four-fraction and eight-fraction scheme.

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