A proposal for a Geant4 physics list for radiotherapy optimized in physics performance and CPU time

We have studied each of the physics options that Geant4 offers to simulate an X-ray radiotherapy treatment with the aim of obtaining those that provide the best possible match to the experimental data of dose profiles and at the same time reduce the CPU time. The procedure has been repeated for two linac setups: an ELEKTA Versa HD with an Agility Multileaf Collimator using two nominal energies, 6 MV and 10 MV, both without flattening filter. After combining the results with those of a previous similar study of a 6 MV VARIAN Clinac 2100 C/D linac with flattening filter, we can propose a set of optimized Geant4 physics options of general use for radiotherapy simulation. Together with this, we have optimized the CPU time using several of the optimization techniques that GAMOS offers, reaching a reduction of several hundred times for each setup.