Department of Clinical Oncology, Prince of Wales Hospital, Hong Kong SAR, People's Republic of China.
Department of Clinical Oncology, The Chinese University of Hong Kong, Hong Kong SAR, People's Republic of China.
Phys Med Biol. 2021 Oct 14;66(20). doi: 10.1088/1361-6560/ac2b83.
The feasibility of magnetic-field-modulated radiotherapy (MagMRT) with an MR-LINAC was investigated by studying the effects of dose enhancement and reduction using a transverse magnetic field with a longitudinal gradient applied along a photon radiation beam.Geant4 simulation toolkit was used to perform Monte Carlo simulations on a water phantom with the energy spectrum of a 7 MV flattening-filter-free photon beam from an Elekta Unity system as the source of radiation. Linear magnetic field gradients with magnitudes ranged from 1 to 6 T cmand spatial extents of 1-3 cm were used to study the dependence of dose modulation on these two parameters. The effects of radiation field size and the ability of dose modulation through optimizing the waveform of magnetic field variation were also explored.Our results show that dose enhancement and reduction can be achieved by applying a transverse magnetic field with a longitudinal field gradient along a photon beam. The steeper the gradient, the more prominent is the effect. A dose enhancement of 33% and a dose reduction of 22% are found for a magnetic gradient of 6 T cmand -6 T cmrespectively. The spatial extent of the dose modulation effect which is greater than 3% is found to be around 1-2 cm. Both the dose enhancement and reduction effects are independent of the radiation field sizes, but they exhibit different behaviors with the spatial extents of the gradient. Multiple locations of dose enhancement and reduction can be produced by modulating the waveform of the magnetic field variation along the radiation beam, demonstrating a vast degree of freedom in the modulation aspect of MagMRT.MagMRT is a conceptually feasible and promising new radiotherapy modulation technique along the direction of the radiation beam.
利用磁线性加速器（MR-LINAC）进行磁场调制放射治疗（MagMRT）的可行性，通过研究施加沿光子射束的纵向梯度的横向磁场对剂量增强和减少的影响来进行研究。使用 Geant4 模拟工具包对具有 Elekta Unity 系统的 7 MV 无均化滤过光子射束能量谱的水模体进行了蒙特卡罗模拟，将辐射源。线性磁场梯度幅度范围为 1 至 6 T cm，空间范围为 1 至 3 cm，用于研究剂量调制对这两个参数的依赖性。还探索了辐射场大小的影响以及通过优化磁场变化波形来进行剂量调制的能力。我们的结果表明，通过沿光子射束施加具有纵向梯度的横向磁场，可以实现剂量增强和减少。梯度越陡峭，效果越明显。对于 6 T cm 和-6 T cm 的磁场梯度，分别发现剂量增强 33%和剂量减少 22%。发现剂量调制效果的空间范围大于 3%，约为 1-2 cm。剂量增强和减少效果与辐射场大小无关，但它们与梯度的空间范围表现出不同的行为。通过沿射束调制磁场变化的波形，可以产生多个剂量增强和减少的位置，证明了 MagMRT 在调制方面具有很大的自由度。MagMRT 是一种沿辐射束方向的概念上可行且有前途的新放射治疗调制技术。
