A novel electron accelerator for MRI‐Linac radiotherapy. Issue 3 (17th February 2016)

• Record Type: Journal Article
• Authors: Whelan, Brendan; Gierman, Stephen; Holloway, Lois; Schmerge, John; Keall, Paul; Fahrig, Rebecca
• Is Part Of: Medical physics. Volume 43:Issue 3(2016)
• Page Start: 1285
• Page End: 1294
• Publication Date: 2016-02-17
• Subjects: biomedical equipment -- biomedical MRI -- electron accelerators -- linear accelerators -- radiation therapy -- superconducting magnets; Therapeutic applications, including brachytherapy -- Linear accelerators -- Accelerators -- Magnetic resonance imaging -- Superconducting magnets; magnetic levitation devices; Involving electronic [emr] or nuclear [nmr] magnetic resonance, e.g. magnetic resonance imaging -- Radiation therapy -- Superconducting magnets; Superconducting coils -- Linear accelerators; MRI linac -- linear accelerator -- finite element modelling -- electron beam -- RF modelling; Cathodes -- Magnetic fields -- Linear accelerators -- Electron sources -- Magnetic resonance imaging -- Direct current power transmission -- Accelerated electron beams -- Magnetic shielding -- Radiation therapy; Medical physics -- Periodicals; Medical physics; Geneeskunde; Natuurkunde; Toepassingen; Biophysics; Periodicals; Periodicals; Electronic journals; 610.153
• DOI: 10.1118/1.4941309
• Languages: English
• ISSNs: 0094-2405

Abstract

Abstract : Purpose: MRI guided radiotherapy is a rapidly growing field; however, current electron accelerators are not designed to operate in the magnetic fringe fields of MRI scanners. As such, current MRI‐Linac systems require magnetic shielding, which can degrade MR image quality and limit system flexibility. The purpose of this work was to develop and test a novel medical electron accelerator concept which is inherently robust to operation within magnetic fields for in‐line MRI‐Linac systems. Methods: Computational simulations were utilized to model the accelerator, including the thermionic emission process, the electromagnetic fields within the accelerating structure, and resulting particle trajectories through these fields. The spatial and energy characteristics of the electron beam were quantified at the accelerator target and compared to published data for conventional accelerators. The model was then coupled to the fields from a simulated 1 T superconducting magnet and solved for cathode to isocenter distances between 1.0 and 2.4 m; the impact on the electron beam was quantified. Results: For the zero field solution, the average current at the target was 146.3 mA, with a median energy of 5.8 MeV (interquartile spread of 0.1 MeV), and a spot size diameter of 1.5 mm full‐width‐tenth‐maximum. Such an electron beam is suitable for therapy, comparing favorably to published data for conventional systems. The simulated accelerator showed increased robustness to operation in in‐line magnetic fields, with a maximum current loss of 3% compared to 85% for a conventional system in the same magnetic fields. Conclusions: Computational simulations suggest that replacing conventional DC electron sources with a RF based source could be used to develop medical electron accelerators which are robust to operation in in‐line magnetic fields. This would enable the development of MRI‐Linac systems with no magnetic shielding around the Linac and reduce the requirements for optimization of magnetic fringe field, simplify design of the high‐field magnet, and increase system flexibility.