Activation of the IBA Proteus One Proton Therapy Beamline Using BDSIM and FISPACT-II

Cyclotron-based proton therapy systems generate large fluxes of secondary particles due to the beam interactions with the beamline elements, with the energy degrader being the dominant source. Compact systems exacerbate these challenges for concrete shielding and beamline element activation. Our implementation of the Rigorous Two-Step method uses Beam Delivery Simulation (BDSIM), a Geant4-based particle tracking code, for primary and secondary particles transport and fluence scoring, and FISPACT-II for time-dependent nuclear inventory and solving the rate equations. This approach is applied to the Ion Beam Applications (IBA) Proteus®ONE (P1) system, for which a complete model has been built, validated, and used for shielding activation simulations. We detail the first simulations of the activation on quadrupole magnets in high-fluence locations downstream of the degrader. Results show the evolution of the long-lived nuclide concentrations for short and long timescales throughout the facility lifetime for a typical operation scenario.