Gantry for a particle therapy system

A particle therapy system comprising:

• a particle accelerator configured to output particles as a particle beam;
• a gantry comprising:
• a beamline structure configured to direct the particle beam, the beamline structure having an efficiency of 10% or more and a length of 6 meters or less;
• a support structure on which part of the beamline structure is mounted and over which the part of the beamline structure is configured to move;
• and
• an energy degrader that is downstream of the beamline structure relative to the particle accelerator, the energy degrader being configured and controllable to change an energy of the particle beam;
• wherein the efficiency of 10% or more includes 10% or more of the particles output from the particle accelerator being output from the beamline structure.