ESTRO 2022 - Abstract Book

S1335

Abstract book

ESTRO 2022

these processes on the molecular and cellular level, we aim to investigate dose averaged Linear Energy Transfer (LET d ) on the micrometer scale in 3D and link it to DNA damage complexity and repair pathways. This in combination with the study of repair kinetics in HNSCC cell lines and patient-derived tumor samples after irradiation, we strive towards a biologically driven radiotherapy treatment selection approach. Materials and Methods Through a joint program from ErasmusMC, TUDelft, HollandPTC, ANSTO and University of Wollongong we are working towards this goal through a combined biophysical modelling and experimental approach. The first step taken towards achieving this goal from the physics stream of the program was the development of a detailed Monte Carlo based simulation platform of the R&D proton beamline at HollandPTC. This was done not only to characterise the system, but also to optimise for radiobiological experiments. Characterisation of the beam envelope in Geant4 was performed through a full parameter sweep of the four beam parameters (lateral spread and angular divergence, in x and y) at multiple energies, whereupon the model was validated with measured data for both pencil beam and the passive scattering system. The second step was the implementation of microdosimetry at HollandPTC through the use of a solid-state silicon-on-insulator (SOI) microdosimeter based on an array of micron-sized 3D sensitive volumes. LET d in these cell-like structures will be measured in 3 dimensions: at different locations within our field of interest (r = 5 cm) produced by the passive scattering system and at different depths along the Bragg curve. Results The model with the optimised beam parameters was tested on independent pencil beam data and shows agreement with measured data within 7%. Implementation of the beam parameters in the passive scattering system in Geant4 (figure 1) shows a uniformity in the x-direction of 97.5% versus a uniformity of 97.7% in measured data in our field of interest (figure 2), with similar results in the y-direction. Further experimental results regarding the LET d measurements and their validation with respect to the developed model will be presented.

Conclusion We propose the 3D LET characterisation of the HollandPTC R&D proton beamline in both pencil beam and passive scattering configuration. The model was validated with measured data, which enables us to start with in-vitro studies of cellular