S2510
Radiobiology - Biology of novel irradiation techniques
ESTRO 2026
xenografts were implanted in ovo onto the chorioallantoic membrane (CAM) of the chick embryos. Tumors were treated with escalating doses of MRT (2, 4, 6, 8, and 10 Gy valley doses with corresponding 152, 304, 457, 609, and 761 Gy peak doses) at the European Synchrotron Radiation Facility. Primary tumor endpoints were assessed as well as metastatic burden in the lower CAM, liver, lung, and brain of the chick embryos. Irradiated and control tumors underwent RNAseq analysis. Results: Analysis of survival at experimental endpoint revealed a 100% survival rate for the groups treated with 2/4/6- Gy valley MRT and unirradiated controls. A small rate of death embryos was found at higher doses in the 8 and 10-Gy valley dose groups. Quantification of proliferation of tumour cells in the MDA-MB-231 tumors revealed a dose-dependent decrease of proliferation, statistically significant in the MRT 8-Gy and 10-Gy valley dose. The presence of metastatic cells in the lower CAM, liver, lung, and brain of the chick embryos was determined by GFP immunostaining, expressed by the breast cancer cell lines. The metastatic quantification by qPCR revealed a general decrease in metastasis formation in treated embryos versus unirradiated CTR, with a more marked effect in liver and brain. Bioinformatic analysis reveals a dose- dependent activation of genes related to cancer cell death as well as modulation of genes associated with pathways known to be involved in the Epithelial- Mesenchymal Transition. Conclusion: This study presents, for the first time, an investigation into the relationship between MRT and metastatic potential employing a chick embryo model, highlighting the importance of understanding this association. MRT shows promise not only in controlling primary TNBC tumours, but also in controlling the spread of metastatic disease, which is the main cause of death in TNBC patients. Keywords: sub-millimeterSFRT, chick embryos, breast cancer
toxicity, with a higher number of affected animals as the time of the inter-pulse pauses increased. Skin toxicity was observed in 10%, 10%, and 45.5% of mice in the 40s, 80s, and 120s pulse-splitting groups, respectively, compared to 77.78% in the CONV group. Conclusion: These findings highlight the critical impact of temporal scheme of dose delivery in defining the FLASH effect. In our model, dose fractionation does not compromise the FLASH effect, whereas pulse splitting leads to its loss, as shown by the increasing incidence of skin toxicity with longer inter-pulse pauses, particularly when exceeded 2min. Keywords: Flash Skin toxicity physical parameters Proffered Paper 3020 Microbeam radiotherapy shows promise for metastatic triple negative breast cancer: insights from a dose-escalation chick embryo study. Verdiana Trappetti 1 , Jennifer Fazzari 2 , Alan Toh 3 , Paolo Pellicioli 1 , Maximillian Jaquerod 1 , Cristian Fernandez- Palomo 1 , Ismael Sanchez Gonzalez 1 , Prateek Arora 1 , David Reparaz 1 , Ilaria Di Manici 4 , Michael Krisch 4 , Chloé Prunier 5 , Emilien Dosda 6 , Michael P MacManus 7 , Erik W Thompson 3 , Robin L Anderson 8 , Olga A. Martin 9 , Valentin Djonov 1 1 Institute of Anatomy, University of Bern, Bern, Switzerland. 2 Department of Radiation Oncology, Mayo Clinic, Rochester, MN, USA. 3 School of Biomedical Sciences, Queensland University of Technology, Brisbane, Australia. 4 ID17, ESRF, Grenoble, 7 Department of Radiation Oncology, Peter MacCallum Cancer Centre, Melbourne, Australia. 8 Metastasis Research Laboratory, Olivia Newton-John Cancer Research Institute, Heidelberg, VIC, Australia. 9 School of Physics, University of Wollongong, Wollongong, Australia France. 5 R&D, Inovotion, La Tronche, France. 6 Production, Inovotion, La Tronche, France. Purpose/Objective: Microbeam Radiation Therapy (MRT) is a form of sub- millimeter spatially fractionated radiotherapy that has demonstrated an excellent therapeutic ratio against cancer in preclinical studies. However, its therapeutic effect on human triple-negative breast cancer (TNBC), and its potential to control the metastatic spread of surviving cancer cells after treatment, remain unclear. Following conventional radiotherapy (RT) for curative purposes in cancer treatment, distant metastasis commonly occurs. This project aimed to assess whether MRT could control TNBC and whether it might suppress tumour cell spread. Material/Methods: Human MDA-MB-231 triple negative breast cancer
Digital Poster 3060
Optimizing dose and dose rate parameters for electron FLASH radiotherapy: a dual-threshold framework to mitigate skin toxicity Shun Lu, Jie Zhou, Yufeng Shen, Xianliang Wang Precision Radiation in Oncology Key Laboratory of Sichuan Province, Sichuan Cancer Hospital & Institute, Affiliated Cancer Hospital of University of Electronic Science and Technology of China, Chengdu, China
Purpose/Objective: The mitigation of acute skin toxicity by electron FLASH
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