SU‐E‐T‐239: Monte Carlo Modelling of SMC Proton Nozzles Using TOPAS

Abstract

Purpose:To expedite and cross‐check the commissioning of the proton therapy nozzles at Samsung Medical Center using TOPAS.Methods:We have two different types of nozzles at Samsung Medical Center (SMC), a multi‐purpose nozzle and a pencil beam scanning dedicated nozzle. Both nozzles have been modelled in Monte Carlo simulation by using TOPAS based on the vendor‐provided geometry. The multi‐purpose nozzle is mainly composed of wobbling magnets, scatterers, ridge filters and multi‐leaf collimators (MLC). Including patient specific apertures and compensators, all the parts of the nozzle have been implemented in TOPAS following the geometry information from the vendor. The dedicated scanning nozzle has a simpler structure than the multi‐purpose nozzle with a vacuum pipe at the down stream of the nozzle.A simple water tank volume has been implemented to measure the dosimetric characteristics of proton beams from the nozzles.Results:We have simulated the two proton beam nozzles at SMC. Two different ridge filters have been tested for the spread‐out Bragg peak (SOBP) generation of wobbling mode in the multi‐purpose nozzle. The spot sizes and lateral penumbra in two nozzles have been simulated and analyzed using a double Gaussian model. Using parallel geometry, both the depth dose curve and dose profile have been measured simultaneously.Conclusion:The proton therapy nozzles at SMC have been successfully modelled in Monte Carlo simulation using TOPAS. We will perform a validation with measured base data and then use the MC simulation to interpolate/extrapolate the measured data. We believe it will expedite the commissioning process of the proton therapy nozzles at SMC.