ESTRO 2023 - Abstract Book

S1503

Digital Posters

ESTRO 2023

PO-1781 Monte Carlo simulations and verification of a commercial image guided small animal irradiator

C. Koksal Akbas 1,2 , A. Spinelli 1

1 San Raffaele Scientific Institute, Experimental Imaging Center, Milan, Italy; 2 Istanbul University Oncology Institute, Medical Physics Department, Istanbul, Turkey Purpose or Objective Preliminary studies have shown that minibeam radiotherapy (MBRT) can be delivered using commercial small animal irradiators. Monte Carlo simulations are robust tool to obtain optimum design of collimators used for generating minibeams. The aim of this study is to validate Monte Carlo (MC) modelling of a commercial small animal irradiator (SmART, PXI) system in order to perform MBRT-MC simulations. Materials and Methods The TOPAS v 3.8.1 Monte Carlo code based on Geant4 v geant4.10.07.p03 was used for all simulations. The X-ray source energy spectrum was calculated by SpekCalc using the manufacturer information. Standard collimators shaping 10x10 mm2, 20x20 mm2, and 40x40 mm2 square beams were modeled and the “g4em-standard_opt4” physics list was used. The cut for all particles was set to 1 µm without any variance reduction techniques. The dose to medium was scored in 0.5x0.5x1 mm3 voxels for the dose profiles (DP) at the phantom (PMMA slabs, 2.5 mm thickness) surface and in steps of 0.5 mm for the depth doses (DD). 3x1011 primary photons were simulated and the verification of the MC simulations were conducted using film dosimetry. The DP at phantom surface were measured with Radiochromic EBT3 (GC) films for 10x10 mm2, 20x20 mm2, and 40x40 mm2 collimator. The DD measurement for 40x40 mm2 was performed by placing GC films between PMMA slabs. All films were scanned at 150 dpi resolution and 48 bit color depth 24 hours after irradiation. The full width half maximum (FWHM), geometric penumbra, and percentage DD were measured and compared to the MC simulations one. Results The lateral dose profiles and depth dose (for 40x40 mm2) are shown in Figure 1. The dose differences between MC and GC were within 5% in the low dose tail regions of the profiles. A good agreement was obtained between simulated and measured PDD with a maximum difference of 2%. The simulated FWHM and penumbra values indicated an excellent agreement with GC film with a maximal discrepancy of 0.319 mm and 0.890 mm for all field s, respectively (Table 1).

Conclusion Monte Carlo simulations of a commercial image guided small animal irradiator were verified using by film dosimetry. Future work will use this MC model to investigate the output of minibeam collimators.

PO-1782 Dosimetric comparison between gated and ungated SBRT plans using VMAT with FFF beams