SU‐E‐T‐672: Macro Monte Carlo for Protons: Proof of Principle

Abstract

Purpose: For electron beams the macro Monte Carlo (MC) technique is well‐established. This work describes the proof of principle of a new macro MC method for proton beams in order to gain computational efficiency. Methods: The proof of principle is performed for the transport of primary protons in water. Pre‐simulations of mono‐energetic proton pencil beams ranging from 10 to 250 MeV impinging perpendicularly on water slabs of different thicknesses (1–10 mm) have been carried out using Geant4. The lateral displacement, the energy‐loss and the direction of all exiting primary protons have been scored and converted into probability density functions (PDFs). The macro MC method consists of stepwise transporting protons by selecting appropriate slab thicknesses and by means of sampling from corresponding PDFs. The sampled energy‐loss is deposited along the path between the entrance and exit positions of the proton for the current step. For validation purposes, different mono‐energetic proton pencil beams impinging on a water phantom, the dose distributions for the primary protons have been calculated using the macro MC transport and Geant4. The resulting integral depth dose curves and dose profiles have been compared. Results: The calculated integral depth dose curves agree better than 1% or 1 mm for all pencil beams considered. The agreement between the dose profiles at several depths in water is within 1% or 1 mm for all energies and depths. The computational efficiency for the macro MC method is about 200 times higher than for Geant4. Conclusions: The results of the dose comparisons demonstrate the very accurate and efficient dose calculation of primary protons using the macro MC method. In future, the macro MC method will be extended to include patient materials and the secondary particle transport in order to allow patient dose calculations for proton beams.This work was supported by Varian Medical Systems.