GMC ['gimik]: a one-variable Monte Carlo dose algorithm for proton therapy

Abstract

This work presents the CPU implementation of GMC ['gimik]: a fast yet accurate one-variable Monte Carlo dose algorithm for proton therapy to be incorporated into our in-house treatment planning system, Astroid. GMC is based on a simple mathematical model using the formulated proton scattering power and tabulated data of empirical depth-dose distributions. These Bragg peaks determine the energy deposited along the particle's track. The polar scattering angle is based on the particle's local energy and the voxel's density, while the azimuthal component of that scattering angle is the single variable in GMC, uniformly distributed from 0 to 2π. The halo effect of the beam, currently not implemented, will consider large scattering angles and secondary protons for a small percentage of the incident histories. GMC shows strong agreement with both the empirical data and GEANT4-based simulations. Its current CPU implementation runs at ~300 m.s^−-1, approximately ten times faster than GEANT4. Significant speed improvement is expected with the upcoming implementation of multi-threading and the portage to the GPU architecture. In conclusion, a one-variable Monte Carlo dose algorithm was produced for proton therapy dose computations. Its simplicity allows for fast dose computation while conserving accuracy against heterogeneities, hence drastically improving the current algorithms used in treatment planning systems.