A COMPACT SUPERCONDUCTING 330 MeV PROTON GANTRY FOR RADIOTHERAPY AND COMPUTED TOMOGRAPHY

The primary advantage of proton beam therapy as a cancer treatment is its ability to maximize the radiation dose delivered to the target volume and minimize the dose to surrounding healthy tissue, due to the inherently narrow Bragg peak at the end of the proton range. This can be further enhanced by imaging the target volume and surrounding tissues using proton computed tomography (pCT), which directly measures the energy loss from individual protons to infer the relative stopping power of the tissues. Proton energies up to 330 MeV are required for pCT. We describe a superconducting gantry design which can deliver protons for both therapy and pCT with a similar size to existing treatment gantries. The use of ten identical combined-function superconducting dipole magnets minimizes the weight and technical development required. Based on experience with superconducting magnets for carbon gantries it should be possible to change the magnetic field sufficiently quickly to perform spot-scanning over successive layers without inducing quenching. It is envisaged that a combination of cryogenic cooling and cryogen-free cooling will be used to achieve the required operating temperature for the magnet windings.