The performance and magnetic shielding of a 6 MV in-line linac in a parallel linac-MR configuration

Abstract

To achieve real-time image-guided radiation therapy, the integration of a linear accelerator (linac) with a magnetic resonance (MR) imager has been proposed. This thesis presents work that investigated performance and magnetic shielding of a linac in the presence of parallel magnetic flux densities. This work used computer simulations and numerical techniques such as finite element and particle tracking algorithms. It showed that a linac can operate with only a 17 ± 1 % target current lost and maintain its treatment beam’s symmetry in the presence of 0.011 T parallel magnetic flux densities. Furthermore, the target current lost is the result of the altered electron gun optics when parallel magnetic flux densities are present. Minimal magnetic shielding (such as a 5-mm-thick, 146.5-mm-long passive shield or a pair of active shield coils with 625 and 430 A turns) around the electron gun and waveguide was demonstrated to recover this lost target current.