Preliminary Magnetic Design of a Superconducting Dipole for Future Compact Scanning Gantries for Proton Therapy

Proton therapy is a rapidly developing technique in cancer treatment since the radiation dose delivered to the target volume is maximized and the dose to surrounding healthy tissue is minimized. The 3-D scanning-irradiation method is performed by means of fast sweeper magnets for transverse scanning, and the scanning in depth of the tumor is performed by fast energy changes in steps of 1% in less than 100 ms. Therefore, high magnetic field ramping speed is necessary. To aim the scanning beam from all directions to the tumor in the patient, the last part of the beam transport and scanning system are mounted on a rotatable gantry. The last bending magnet in the gantry is a major component that drives the weight, footprint, and costs of the whole machine. Superconducting magnets have the potential to reduce the facility weight and costs, maintaining at the same time a large scanning field size. The preliminary magnetic design of the superconducting dipole for a proton therapy gantry is presented in this paper. The design consists in four Nb 3Sn racetrack coils and considers the requirement of large aperture for the transverse scanning and low field at the patient location using an active shielding system.