A novel electron accelerator for MRI-Linac radiotherapy.

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Accelerator Physics

Background:

• Magnetic Resonance–Linear Accelerator (MRI-Linac) systems integrate radiotherapy with Magnetic Resonance Imaging (MRI) for enhanced precision.
• Conventional electron accelerators in MRI-Linac systems face challenges due to magnetic fringe fields, necessitating complex shielding that can degrade image quality and limit design flexibility.

Purpose of the Study:

• To develop and computationally test a novel medical electron accelerator concept inherently robust to operation within magnetic fields.
• To enable the design of in-line MRI-Linac systems without the need for magnetic shielding around the accelerator.

Main Methods:

• Utilized computational simulations to model an RF-based electron accelerator, including thermionic emission, electromagnetic fields, and particle trajectories.
• Quantified electron beam characteristics (current, energy, spot size) in zero-field and simulated 1 Tesla magnetic fields.
• Assessed the impact of magnetic fields on beam quality and compared performance to conventional accelerator designs.

Main Results:

• The simulated accelerator produced a therapy-suitable electron beam (146.3 mA average current, 5.8 MeV median energy, 1.5 mm spot size).
• Demonstrated significant robustness in magnetic fields, with a maximum current loss of only 3% compared to 85% for conventional systems.
• Performance compared favorably to published data for conventional accelerators in zero-field conditions.

Conclusions:

• Computational simulations suggest that RF-based electron sources can create accelerators robust to in-line magnetic fields.
• This novel concept facilitates the development of MRI-Linac systems without magnetic shielding, simplifying magnet design and increasing system flexibility.
• Eliminating shielding requirements enhances MR image quality and streamlines the integration of radiotherapy and MRI technologies.