Monte Carlo simulation and verification of a scanning proton beam nozzle

Objective To establish an accurate simulation model for proton scanning beam using Monte Carlo (MC) code. Methods The MC model of proton scanning beam treatment nozzle was established by using MC code FLUKA combined with the geometric structure of the treatment nozzle in Shanghai Proton and Heavy Ion Center (SPHIC). The MC beam model was established through the simulation of the integrated depth dose distribution (IDD) in water and the lateral profile in air at the isocenter points. The model was used to simulate the depth and lateral dose profile of Spread Out Bragg Peak (SOBP) of proton beam. The calucated result were compared with TPS calculation values. Results For the distal R90, the deviations of simulation and measurement at all energies were less than 0.5 mm. For distal fall off (R80-20), the deviations between simulation and measurement at each energy were within 0.1 mm. The biggest difference between measurement and simulation of the proton beam spot size was within 0.45 mm. The result of simulation and TPS calculation of proton SOBP matched well, with the γ index pass rate being higher than 90% (Criteria: 2 mm, 2%). Conclusions The MC code FLUKA can be used to model the nozzle of scanning proton beam, which can meet the clinical requirements and accurately simulate the proton beam transport in material. After construction and verification on the basis of measurement, this model can be used as a dose verification tool to evaluate clinical proton treatment plans, in order to reduce the beam time for dose verification and thus increase the number of patient treatment in proton therapy. Key words: Monte Carlo; Proton therapy; Treatment nozzle; Scanning beam