Beamlines without midplane symmetry for neutron and proton cancer therapy

With the emergence of neutron and proton irradiation facilities for cancer therapy, substantial interest has developed in compact gantry beamlines which can be rotated around the patient and guide the beam from the rotation axis to the perpendicular irradiation axis. We propose a new type of beamline which differs from other approaches by giving up midplane symmetry but requiring only three bending magnets. Compared to other designs, this layout increases the amount of room for patient and instrumentation while maintaining rather compact exterior dimensions. ck of midplane symmetry conceptually complicates the design in several aspects. However, using solenoids for linear decoupling and focusing, the system can be made linearly achromatic in both planes. In order to achieve the required beam spot size in the transport, careful higher-order correction is necessary, in particular because of the coupling aberrations that arise from lack of midplane symmetry. In the proposed system, the relevant second- and third-order aberrations have been corrected.