Study of magnetic fringe fields and interference effects on beam dynamics for proton facility gantry

Abstract

ABSTRACT Proton therapy facilities require a beamline that effectively delivers particles to a nozzle that forms symmetric and achromatic beam spots. In the gantry lattice of the SC200 facility, the magnetic components are designed with a compact layout due to space constraints. This makes it important to properly deal with fringe fields and their interference when more accurate simulations of beam dynamics are required. In this paper, we establish field distributions based on real extracted magnetic maps and analyse the influences of linear fields on beam qualities by combining a perturbation model with Monte Carlo code in BDSIM. To verify the results, COSY INFINITY with the Enge function was used to quantify the beam variations at the isocenter; the results were in good agreement with those of BDSIM. Compared with the conventional hard edge model, beam mismatch at the isocenter is evidence of the impacts of fringe fields, which pose challenges to clinical dose planning. Hence, linear optical optimization on the gantry is also necessary to meet safety and precision requirements. These efforts will guide the commissioning of the beamline.