Magnet Developments and Commissioning for the IBA Compact Gantry

The ProteusOne gantry will be the first IBA gantry with scanning upstream of the last bending magnet. This configuration offers the combined advantage of compactness and Pencil Beam Scanning (PBS) with reasonable source to gantry axis distance (SAD). This new proton therapy gantry required modifications on existing IBA beam line magnets as well as development of new ones. This paper presents the basic features and advantages of the gantry optics and details the magnets that needed to be designed. In addition, some specific issues raised by the gantry compactness will be detailed. The scanning magnet and the last, wide gap, bending magnet required special attention to ensure good quality beam optics. Indeed, due to the small distance between them, careful design is required to minimize their mutual influence. Parts of the gantry structural elements also had to be taken into account, adding complexity to the magnetic modeling and requiring very good collaboration between beam optics and mechanical design teams. Finally, some details of the commissioning of the magnets and model crosschecks are also presented.