University of Manchester

Gantry Design for Linac-boosted Protons

Trainee: Ewa Oponowicz
Supervisor: Hywel Owen

Proton computed tomography (pCT) is proposed to achieve a more precise dose delivery. Replacing conventional imaging techniques with pCT will reduce uncertainties of proton therapy planning.

However, for an adult patient it requires a beam kinetic energy of approximately 330 MeV, compared to a maximum 230 MeV therapeutic beam. Due to the high energy (high rigidity) requirements and space limitations for a proton beam suitable for pCT, there is no design of a rotating beam delivery system for this application yet.

The overall goal of this project was to develop a detailed beam-optical and magnet design for a combined-function superconducting gantry for proton CT within the Research Beamline Room in Proton Therapy Centre at the Christie Hospital in the UK. The beam energy is proposed to be increased with a booster linear accelerator. The preliminary beam delivery system is a double achromat design with a pencil beam scanning system located downstream of the final bending section. An isocentric design is employed since it has been proven to be effective, flexible and is most widely used in proton centres. The gantry design consists of normal-conducting quadrupoles and superconducting, canted-cosine theta bending magnets.

Within this project, studies on the novel beam energy degrader were carried out in collaboration with the Center for Proton Therapy at Paul Scherrer Institute, Switzerland. The current graphite degrader has beem replaced with boron carbide in order to improve the beam transmission from the cyclotron to the isocentre and to achieve a clinical beam with the best characteristics.

Additionally, the beam energy degrader and high-gradient structures were incorporated into the system and beam tracking studies of the delivery line including the complete magnetic design were performed. The beam delivery system was also amended such that beam diagnostics instruments, a cryogenic system or mechanical structures can be added into the arrangement.