A hybrid numerical approach to the propagation of charged particle beams through matter for hadron therapy beamline simulations

In hadron therapy beamlines, passive elements are used to reduce the beam energy or to shape its transverse profile and frequently complement the magnetic transport channel elements. In particular, cyclotron-based facilities feature energy degraders to tailor the energy to the treatment value. As such, the numerical modeling of hadron therapy beamlines is crucially reliant on the accuracy of the available beam–matter interaction models to simulate the beam properties at levels suitable for clinical applications. While integrated Monte Carlo codes reach these accuracy levels, ultra-fast numerical codes are essential for beam commissioning controls applications or fast iterative optimization of new designs. To that end, we propose a novel effective model to compute the beam–matter interactions in a hybrid fashion, using tabulated range tables, the semi-analytical Fermi–Eyges approximation, and fits extracted from Monte Carlo data. In this work, we detail the method and benchmark each step with Geant4 simulations. Finally, we validate its accuracy with beam-based measurements from a proton therapy facility using our Python-language implementation which is shown to provide computation time of the order of milliseconds. The results are discussed in detail. •Monte Carlo implementation of Multiple Coulomb Scattering of protons.•Effective model for Multiple Coulomb Scattering, nuclear scattering and inelastic collisions.•Optimization of hadron therapy beamlines with fast tracking code.