Compact proton therapy system with energy selection onboard a rotatable gantry

A radiation therapy system for irradiating an irradiation object with particle beams of a predetermined energy, said radiation therapy system comprising:

• a particle accelerator configured to provide a particle beam for a single treatment station;
• a beam line assembly coupled to said particle accelerator and operable to direct said particle beam along a first direction;
• an energy degrader operable to attenuate an energy of said particle beam;
• and
• a gantry assembly coupled to said beam line assembly and comprising dipole magnets configured to generate variable magnetic fields,
• wherein said variable magnetic fields are operable to select a portion of said particle beam with said predetermined energy for irradiating said irradiation object and redirect said portion of said particle beam to a predetermined direction.