ESTRO 2023 - Abstract Book

S1723

Digital Posters

ESTRO 2023

The GATE and GEANT4-DNA MC software was applied for simulations of energy depositions from proton beams of energies 1, 2, 5, 10, 20, 50 and 100 MeV in water. The simulations were performed using three different Sensitive Volumes (SV) with cube sides of 0.5, 2 and 20 µm (Figure 1a) obtaining microdosimetric distributions for sites of (10, 20, 50, 100, 200 and 500 nm), (1 and 2 µ m) and (5, 10 and 20 µ m), respectively. Charged particle equilibrium was obtained in the SV for all simulations. To reduce computational time, a virtual site concept (Figure 1b) was introduced, where the data was analyzed using the maximum number of virtual spheres that could fit within the SV. The number for virtual sites ranged from 1 (20 µ m) to125 000 (10 nm). Results The virtual site concept enabled efficient reuse of simulation data to calculate y distributions for different site sizes. When the site size is reduced the distributions of y widens (Figure 1c-f) and the dose-averaged y , yd , increases for all proton energies (Figure 2). Furthermore, with increasing proton energy, the lineal energy distributions are shiftet towards lower y , and the distributions generally becomes wider (Figure 1c-f). This implies that the lower energy protons deposits more energy per event, and that there is higher variance in how much energy each event deposits for higher energy protons. For 10 MeV protons, yd increases from 5.4 to 19.5 keV/µm when decreasing the site diameter from 1 µm to 10 nm (Figure 2b), Illustrating that y measured with different detectors cannot directly be compared. yd does not change as much for larger sites and is almost constant from 20 to 1 µm.