A radiation therapy system comprises a beam delivery system located in a treatment room. The beam delivery system comprises a particle accelerator for generating a radiation beam, and a positioning apparatus for moving the particle accelerator to any one of a plurality of treatment locations in said treatment room. The system includes a plurality of waiting rooms each having a patient support apparatus that is movable between a waiting state in which it is located in the respective waiting room, and a treatment state in which it is located in a respective one of the treatment locations in the treatment room.The positioning apparatus comprises a counterbalanced lever which carries the particle accelerator.The particle accelerator is preferably a proton accelerator producing a proton beam.
