Design of the Energy Selection System for Proton Thera- Py Based on Geant4*

Huazhong University of Science and Technology (HUST) has planned to build a proton therapy facility based on an isochronous superconducting cyclotron. The 250 MeV/500 nA proton beam is extracted from a superconducting cyclotron. To modulate beam energy, an energy selection system is essential in the beamline. The simulation based on Geant4 has been performed for the energy selection system and its result will be discussed in this paper. This paper introduces the variation rules of the beam parameters including the beam energy, beam emittance, energy spread and transmission. The degrader’s gap and the twiss parameter are proven to be effective ways to reduce the emittance after degrader.