Parallel tally geometry in GEANT4 for medical dose calculation

The use of Monte Carlo calculation is essential in radiation therapy. Monte Carlo simulation is widely used for verifying the dose for nozzle design, quality assurance, and the treatment planning system. GEANT4 simulation toolkit provides many powerful functions suitable for the dose calculation in radiation therapy. In radiation therapy, both a simple homogeneous water phantom and a complex volume extracted from CT data are used for the dose calculation. Therefore, universal access to the particle information regardless to the complexity of the geometries is desirable. We extended functionalities of GEANT4 to allow two independent geometries in one simulation application simultaneously, where one geometry represents real materials and the other represents an artificial geometry for a tally. In this report, we describe the parallel tally geometry in GEANT4 for medical dose calculations. We also report the validation results of this new capability