ABSTRACT
Objective: To investigate the impact of MR fringe magnetic field on the electron beam characteristics of the electron gun in the MRI-guided radiotherapy (MRIgRT). Methods Electromagnetic field analysis software was used to simulate the beam characteristics of both Litton L2087 electron gun and Varian 600C electron gun under different magnetic field strengths for the in-line MRIgRT configuration. Results Two electron guns exhibited qualitatively similar behavior in the fringe magnetic field. As field strength increased, the current emitted by the cathode increased slowly, which could increase up to 2.72% and 1.93% from the original value without external magnetic field for Litton L2087 and Varian 600C electron gun, respectively. The current at the anode exit started to decrease after the initial plateau, and after reaching a minimum value, the current started to increase slowly, and the current loss could reach up to 80.25% and 73.48% of the initial value, respectively. At high values of the field strength, the beam radius changed periodically. Beam root mean square emittance fluctuated under different magnetic field strengths. Conclusion For in-line MRIgRT configuration, the fringe magnetic field can affect the trajectory of the beam and cause a large amount of current loss in the electron gun, and the beam RMS emittance varies greatly.
ABSTRACT
Being the basic means in accurate and precise radiotherapy, image-guided radiotherapy can target the tumor and visualize the adjacent organs at risk. Compared with MR scanners, imaging devices based on X-ray imaging have disadvantages such as poor soft tissue contrast and radiation. In recent years, the integrated and real-time MR imaging-guided radiotherapy (MRIgRT) technology, which combines MR scanner and the radiotherapy machine, open a new horizon in radiation therapy. The technical advantages of MRIgRT, the research status of MRIgRT equipment at home and abroad, and the technical challenges of MRIgRT were reviewed in this article.