Beam physics simulations of the IBA Proton Therapy Compact Gantry.

The latest IBA Proton Therapy system is a compact solution featuring a superconducting synchrocyclotron and a compact gantry. The compact gantry supports the state-of-the-art active scanning Pencil Beam Scanning technique. The gantry system can rotate around the patient to offer multiple beam incidence angles for tumor irradiation. With that method a small round beam is scanned over the tumor volume, allowing for an improved dose conformity compared to earlier techniques. This beam delivery method puts strong constraints on the beam properties. The goal of this study is to use simulation software (MAD-X and home-built Python libraries) to assess, challenge and improve the design of the gantry optics; to provide a high performance and robust solution. The simulation results are compared with experimental data from the IBA installations in Detroit (US) and Newport (UK). The simulations study and compare results obtained for the beamline transmission efficiency through the gantry, for the beam optics and for the beam scanning pattern at isocenter as a function of the gantry angle and other key parameters. In order to make full use of the model, specific Python code has been developed to convert and generate beamline models, to extract and interpolate operational settings (e.g. magnet currents and collimator apertures) and to perform in-depth analyses of the results. The model is currently waiting for a more thorough experimental validation, nonetheless, the simulations already provide a qualitative study of the beam parameters at isocenter plane, i.e. on the transversal tumor plane and key quantitative figures. Most importantly, measured transmission efficiencies have been modeled for the first time. Additionally, we provide insights for future developments required to improve the model’s accuracy and practical usability.