Beam optics design of compact gantry for proton therapy.

A new proton therapy facility for the treatment of deep-seated tumours is being assembled. The proton beam will be applied to the patient under computer control, using dynamic scanning of a focused proton pencil beam to produce a complete three-dimensional conformation of the dose to the target volume. The beam will be applied to the supine patient using a compact isocentric gantry for protons. By combining the scanning of the beam with the beam optics and by mounting the patient couch eccentrically on the gantry, the diameter of the rotating structure can be reduced to 4 m, which is the smallest diameter designed so far for a proton gantry. The paper describes the project especially from the point of view of the optics of the beam transport system of the gantry, including the beam line used to inject the beam into the gantry.