ESTRO 2025 - Abstract Book

S2344

Interdisciplinary – Other

ESTRO 2025

Conclusion A strong engagement between ESTRO and NS was underlined with the outcomes of this survey. The most striking result is the strong interest in guidelines, best practices and participation in future projects which will help ESTRO better understand NS’s interests and improve its role in advancing radiotherapy in Europe.

Keywords: National Societies - Collaboration - Engagement

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Digital Poster First results of the association of nanodosimetric cluster dose with radiation-induced double-strand breaks foci following microbeam irradiation João F. Canhoto 1,2 , Ana Belchior 3,2 , Reinhard Schulte 4 1 Departamento de Física, Instituto Superior Técnico - ULisboa, Lisboa, Portugal. 2 Centro de Ciências e Tecnologias Nucleares (C2TN), Instituto Superior Técnico - ULisboa, Lisboa, Portugal. 3 Departamento de Engenharia e Ciências Nucleares, Instituto Superior Técnico - ULisboa, Lisboa, Portugal. 4 Division of Biomedical Engineering Sciences, Loma Linda University, Loma Linda, USA Purpose/Objective The association of nanodosimetric quantities with radiation-induced biological damage, such as the yield of double strand breaks (DSBs) [1] or the cell survival fraction [2], has been actively researched in recent years to show that the nanodosimetric ionisation cluster size distribution (ICSD) is closely related to the biological damage more than quantities like the absorbed dose or LET. In recent work [2], we presented a novel concept called cluster dose, g (I p ) - a quantity akin to the absorbed dose that takes into account the spatial distribution of ionisations in nanoscopic volumes (the nanodosimetric parameter I p ). The hypothesis is that there exists an I p such that radiation fields delivering the same cluster dose result in (approximately) the same biological outcome. In this work, we present, for the first time, an association of cluster dose with the yield of DSB foci per particle after microbeam irradiation by protons and helium-ions. Material/Methods HUVEC cells were irradiated with microbeams of 3 MeV protons (LET = 19 keV/µm) and 8, 10 and 20 MeV α-particles (LET = 170, 85 and 36 keV/µm) at the PTB microbeam facility. Using a mathematical model of the irradiation and imaging conditions, the number of DSB foci per particle was inferred from the kinetics of the number of visible foci at 0.5 to 24 hours post-irradiation [3]. The fluence-weighted ICSD in the nucleus was obtained following the procedure in [2], using a sphere of 3.4 nm as the sensitive volume (representing a 10bp DNA segment). The number of DSB foci per unit cluster dose was investigated for different I p calculated from the ICSD. Results The analysis of the experimental data showed a strong association between the DSB foci per cluster dose and I p at lower LET. In this range, a separation metric of DSB foci per cluster dose (Figure 1) reached a minimum for F 4 (frequency of clusters of four or more ionisations). For high LET, data were not consistent with the expected number of foci, most likely due to limitations of the mathematical model used.