Potential Applications of MTS and HTS to MRI Imaging Systems for Particle Beam Therapy

Abstract

<h3>Purpose/Objective(s)</h3> To explore the potential application of medium temperature superconductors (MTS) and high temperature superconductors (HTS) to the development of background magnets for MRI systems for use in combination with particle beam therapy (PBT) and the concept design for MRI-guided PBT. <h3>Materials/Methods</h3> In proton/heavy ion therapy, because of the sharp dose drop off owing to the Bragg peak effect, imaging guidance becomes crucial. Various imaging techniques have been considered, but MRI, with its soft tissue contrast, 3D imaging, high spatial resolution, and potential on-live monitoring feature would be particularly useful in combination with PBT. One of the key challenges is that the charged particle beam will be deflected in a transverse magnetic field. The deflection of the particle beam in the presence of the background B0 has received significant interest, and both in-line and transverse configurations have been considered. For in-line configurations, smaller deflections are seen, with some rotation, and for transverse, greater deflection, and momentum change. With the use of a pencil beam PCT approach in combination with computation, such deflections can in principle be compensated. However, if "real time" imaging is to be enabled, minimum computation and reconstruction time is desirable. For these reasons, minimizing and simplifying the deflection is desirable. This can be enabled with the use of the in-line configuration, but in this case an in-line system compacts enough to mount on a gantry may be of interest. This can be made more achievable with the use of MTS or HTS where less bulky magnets are possible, cooling is simplified, and systems are much less quench sensitive. At the same time, the minimization of fringe fields can also substantially simplify the particle beam trajectories and minimize their deflection. This may also be enabled for open configuration transverse configurations with the use of less bulky HTS and MTS magnets. For this work we performed magnetic modelling of several different configurations of MTS and HTS magnets, both in-line and transverse, using Vector fields and other modelling software. The sizes and configurations of the MTS and HTS systems as compared to potential competing LTS systems were then compared. Particle beam trajectories were then computed with GEANT software and compared. <h3>Results</h3> (1) MTS and HTS systems can allow the development of in-line MR which are sufficiently compact, open, and robust (to quench) to allow mounting on a gantry. This reduces particle beam deflection, while at the same time allowing rotation of the beam around the patient; (2) Several designs for minimized fringe fields are given, both for in-line and transverse configurations. <h3>Conclusion</h3> MTS and HTS have a significant potential for application to MRI-guided Particle Therapy based on their potential for mounting on a gantry, and enabling of more open background magnet configurations. Magnet designs with minimized fringe fields are also possible and useful.