A design of a compact gantry for proton therapy with 2D-scanning

A compact gantry (3 m radius) for proton therapy in which a so-called “pencil” beam scans a 30×30 cm2 surface, has been designed. The advantages of this gantry are its small size and the fact that no mechanical movements of magnets or patient couch are necessary to accomplish the two-dimensional scanning. In our design the pencil beam scanning is performed by two independently working scanning magnets. A compact system has been achieved by integration of the beam scanning into the ion optical design of the gantry. The large deflections of the pencil beam from the optic axis of the gantry have been treated correctly by the ion optics code COSY. The ion optical design of the gantry and the use of COSY for the study of the action of the scanning magnets are discussed.