Beam optics of a compact gantry for carbon-ion radiotherapy

Abstract

We present a beam optics of a compact carbon gantry based on superconducting bending magnets. It transports carbon-ion of 400 MeV/u and covers 4π solid angle around a fixed patient enabling precise radiotherapy. With 5-T dipole field, this gantry has comparable size with existing proton gantries. The gantry provides rotationally invariant optics and a point-to-parallel scanning over an area of 20 cm × 20 cm at the isocenter. This is possible in part with a 90-degree combined-function magnet with 18.6 cm bore radius. The 90-degree combined-function magnet has magnetic field distribution satisfying equal focusing for horizontal and vertical plane, and zero integrated nonlinear fields. With steering upstream of the 90-degree magnet, we scan 20 cm × 20 cm region at the isocenter with nearly round beam. We show three-dimensional field analysis of the 90-degree magnet and particle tracking to validate beam optics of the gantry, and point-to-parallel scanning, and rotationally invariant beam.