MR-PVHEE: A novel magnetic resonance-guided parallel-beam very high-energy electron radiotherapy system

Abstract

PurposeMR-guided very high-energy electron (VHEE) radiotherapy can combine the imaging advantages of MR with the dosimetry advantages of VHEE radiotherapy, which is of significant clinical value. However, VHEEs are highly susceptible to the Lorentz force generated by the MR magnetic field, and coupling MR and VHEEs is challenging. Here, we present a novel MR-guided parallel-beam VHEE (MR-PVHEE) radiotherapy system and confirm its feasibility and effectiveness. MethodThe proposed MR-PVHEE radiotherapy system includes an ingenious coupling model of MR and VHEEs and an electromagnetic steering parameters commissioning (ESP-COM) method for accurate delivery. First, by generating parallel VHEE (PVHEE) beamlets that point in the same direction as the MR main magnetic field, the coupling model based on triple-stage electromagnetic steering can significantly lessen the twisting and deflecting of the VHEE beamlets' delivery trajectory caused by the MR magnetic field. The dosimetric advantage of VHEEs will be enhanced by delicately utilizing the MR magnetic field to constrain lateral scatter. Then, the ESP-COM method based on Bayesian black-box optimization for the PVHEE beamlets is designed by constructing a cost function using the position and direction information of particles in phase space and optimizing the parameters to deliver the beamlets accurately to the target spots. Finite element electromagnetic modeling and Monte Carlo particle transport simulation are used to validate the MR-PVHEE. ResultsMR-PVHEE can generate the PVHEE beamlets in the same direction as the MR magnetic field and accurately deliver them to the target spots. The average position error is within 0.5 mm, and the average direction error is about 0.5°, which can meet the requirements of clinical treatment accuracy. MR-PVHEE can reduce the VHEE lateral penumbra and increase the dose drop gradient. ConclusionFor the first time, MR and VHEE radiotherapy are successfully coupled in this study, and the innovative MR-PVHEE radiotherapy system can elicit new modalities for MR-guided charged particle radiotherapy and spatially fractionated radiotherapy.