ESTRO 2025 - Abstract Book

S3564

Physics - Optimisation, algorithms and applications for ion beam treatment planning

ESTRO 2025

4216

Digital Poster A novel approach to enable dose rate simulations within the chemical phase of Geant4-DNA using the step by-step method David Weishaar 1 , Robin Erdmann 1 , Larissa Derksen 1,2 , Natalie Hornik 1,3 , Boris Keil 1 , Klemens Zink 2,1,3 , Kilian Simon Baumann 1,2,3 1 Institute of Medical Physics and Radiation Protection, University of Applied Sciences, Giessen, Germany. 2 Marburg Ion-Beam Therapy Center (MIT), University Hospital, Marburg, Germany. 3 LOEWE Research Cluster for Advanced Medical Physics in Imaging and Therapy (ADMIT), University of Applied Sciences, Giessen, Germany Purpose/Objective: Treatment with ultra-high dose rates can lead to a different biological response compared to clinical dose rates. This has the potential to enhance normal tissue sparing and improve therapy outcomes [1]. To better understand this effect, incorporating time-dependent energy deposition in Monte Carlo simulations provides insights into the underlying chemical mechanisms. Compared to implemented IRT methods [2], the step-by-step method is more is more accurate and preserves all spatial species information at the cost of a higher computing time. Material/Methods: This work is based on the Geant4-11.2.2 chem6 example [3]. The adaptation of existing classes handling chemical species and temporal structure of the chemical phase allows the addition of any species during the dynamic time steps of the step-by-step (SBS) model. While the physical phase is neglected, user input of total deposited energy and pulse length defines the insertion of pre-captured phase space files. The first step to adapt the code is to analyse the alteration of the reaction processes with the change of the pulse structure. The time evolution of reactions (see Fig.2) affecting H 2 O 2 , which is well comparable to experiments due to its stability, and solvated electrons is simulated for varying pulse widths but the same deposited dose within a water voxel. Results: Figure 1 shows the distribution of chemical species produced after 1 keV energy deposition for one 220 MeV proton. Most of the species are located in the core of the track (x = y = 0), while the solvated electrons are scattered laterally at right after the physical phase. Figure 2 shows the different reactions for simulations with different pulse widths but the same deposited energy. As the pulse width increases, solvated electrons can diffuse and the number of scavenging reactions (2) increases.

Figure 1