The PTSim and TOPAS projects, bringing Geant4 to the particle therapy clinic

Though the Geant4 Simulation Toolkit has been widely accepted in the particle therapy community, with research and clinical use at most of the major centers currently involved in this innovative approach to cancer treatment, the high level of Geant4 expertise required for these applications has proven a serious barrier for users. The PTSim collaboration in Japan and the TOPAS collaboration in the United States wrap and extend the Geant4 toolkit to meet the needs of this critical community. PTSim has provided a common platform to model three Japanese proton and ion therapy facilities plus three more in other countries, allowing users who are not Geant4 experts to accurately and efficiently run Geant4 simulations for any of these pre-built configurations. Building on a rich history of proton therapy applications at MGH (site of the world's first proton therapy system), NCC Korea, and elsewhere, the TOPAS project aims to take flexibility further, allowing any particle therapy clinician or researcher to Geant4-simulate their own real or envisioned facility still without requiring a Geant4 expert. We describe these projects, how their designs bridge the gap between flexibility and ease of use, what key missing software components they have contributed and how the two projects may evolve together. (author)