Pencil beam algorithm on the GEANT4 based simulation framework and verification of the dose distributions for proton therapy

GEANT4 based Monte Carlo simulation has been widely accepted for dose calculation in medical physics. In our previous work, we had developed a GEANT4 based simulation framework for particle therapy system in order to provide a common interface for simulating various irradiation systems. The framework realizes not only comparing simulated results with measurements, but also discussing about the best physics models across different facilities. In this work, a pencil beam algorithm has been introduced in the framework for the purpose of verifying the dose distributions with Monte Carlo simulation. The dose distributions were compared in homogeneous water phantom and CT images of a patient using a treatment parameter at Hyogo Ion Beam Medical Center, respectively. The dose distributions were in good agreement but small disagreements were seen.