Geant4 Simulation for Commissioning of Proton Therapy Centre

In anticipation of the new Proton Therapy Centre in Singapore at 2020, the medical physicists and physicists in NCCS and NUS have come together to do several preparation/preliminary works. Of which, one of the most important programme is to develop the Monte Carlo simulation capability using GEANT4 toolkit. We simulated the entire beam delivery and nozzle based on specifications given by Hitachi. The results of the Energy-Range curves in water phantom together with spot size in air agrees well with measurement data provided by Hitachi. We will show the complete methodology of simulation leading up to the comparison with measurement data. There were 3 main aspects we focused on-(1) The choice of physics models, (2) The determination of initial proton phase space based on Twiss parameters from beam profile measurement and (3) The choice of cut-off energy and step size. This simulation is important for the commissioning of the Proton Therapy System and the methodology presented will be helpful for other upcoming centers who are interested in doing the same.