Experimental validation of proton physics models of Geant4 for calculating stopping power ratio

Abstract

In this work, we conducted experiments to validate the proton physics models of Geant4 (version 10.6). The stopping power ratios (SPRs) of 11 inserts, such as acrylic, delrin, high density polyethylene, and polytetrafluoroethylene, etc, were measured using a superconducting synchrocyclotron that produces a scattering proton beam. The SPRs of the inserts were also calculated based on Geant4 simulation with six physics lists, i.e. QGSP_ FTFP_ BERT, QGSP_BIC_HP, QGSP_BIC, QGSP_FTFP_BERT, QSGP_BERT, and QBBC. The calculated SPRs were compared to the experimental SPRs, and relative per cent error was used to quantify the accuracy of the simulated SPRs of inserts. The comparison showed that the five physics lists generally agree well with the experimental SPRs with a relative difference of less than 1%. The lowest overall percentage error was observed for QGSP_FTFP_BERT and the highest overall percentage error was observed for QGSP_BIC_HP. The 0.1 mm range cut value consistently led to higher percentage error for all physics lists except for QGSP_BIC_HP and QBBC. Based on the validation, we recommend QGSP_BERT_HP physics list for proton dose calculation.

Keywords: Geant4; Monte Carlo simulation; experimental validation; physics lists; stopping power ratio.

Figure 1:

The setup for measuring proton stopping power range. The insert is placed between the brass blockers and the water tank.

Figure 2:

Experimental depth dose curve of air, PTFE, Delrin, Acrylic, and HDPE inserts

Figure 3:

Experimental depth dose curve of air, water, KP-1, KP-2, KP-3, KP-4, Butanol, Propanol, and Ethanol inserts.

Figure 4:

Simulated normalized depth dose curves for all the experimental inserts. The physics model used for this simulation was QGSP_BERT_HP, and the range cut value is 0.01 mm.