Magnet Design and Optimization for an Integrated Linac-MRI System

• Author / Creator

  Tadic, Tony

• A promising approach to the development of an integrated system for magnetic resonance imaging-guided radiotherapy involves the rigid coupling of a medical linear accelerator to a rotating biplanar magnet assembly. Through near real-time volumetric imaging during irradiation, this hybrid system will enable dynamic target localization and online treatment plan optimization. The work presented in this thesis was concerned with the design of non-axisymmetric yoked biplanar magnets that are suitable for use with this integrated system. Namely, the goal of this research was to develop and implement robust optimization algorithms for the design of novel permanent and superconducting magnet assemblies that are compact in size and provide an unobstructed beam path. A nonlinear iterative shape optimization scheme based on the finite element method was developed for the calculation of axisymmetric and non-axisymmetric pole piece surface contours that minimize the magnetic field inhomogeneity in a designated imaging volume. This method was applied to the theoretical design of a full-body 0.2 T biplanar permanent magnet system, for which the necessity of the optimized pole piece designs was demonstrated. The algorithm performance was evaluated and the sensitivity of the optimized designs was investigated. An iterative optimization scheme based on the finite element method was also developed for the calculation of minimum volume coil arrangements for superconducting magnets with magnetic materials. In particular, this method is well suited for the design of conduction-cooled cryogen-free magnet systems employing high-temperature superconducting coil configurations. The effectiveness of the proposed method was demonstrated with a uniform approach to the optimal design of several full-body 0.5 T superconducting biplanar magnet systems with bored yoke structures. These designs were subsequently evaluated with an emphasis on the relationship between the yoke geometries and magnet performance.

• Subjects / Keywords

  • Finite-element-method
  • Magnetic Resonance Imaging
  • Linac-MR
  • Adaptive
  • Linear Accelerator
  • Radiation Therapy
  • Magnet Design
  • MRgRT
  • FEA
  • Optimization
  • Finite-element-analysis
  • Radiotherapy
  • FEM
  • Superconducting Magnet
  • Linac-MRI
  • IGRT
  • Permanent Magnet
  • MRI
  • Linear Programming
  • Nonlinear Optimization

• Graduation date

  Spring 2012

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R32B8VM1V

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.