School of Information Technology and Electrical Engineering, The University of Queensland, St Lucia, QLD 4072, Australia.
Phys Med Biol. 2014 Jan 6;59(1):233-45. doi: 10.1088/0031-9155/59/1/233. Epub 2013 Dec 13.
MRI-LINAC is a new image-guided radiotherapy treatment system that combines magnetic resonance imaging (MRI) with a linear accelerator (LINAC) in a single unit. One drawback is that the pulsing of the split gradient coils of the system induces an electric field and currents in the patient which need to be predicted and evaluated for patient safety. In this novel numerical study the in situ electric fields and associated current densities were evaluated inside tissue-accurate male and female human voxel models when a number of different split-geometry gradient coils were operated. The body models were located in the MRI-LINAC system along the axial and radial directions in three different body positions. Each model had a region of interest (ROI) suitable for image-guided radiotherapy. The simulation results show that the amplitudes and distributions of the field and current density induced by different split x-gradient coils were similar with one another in the ROI of the body model, but varied outside of the region. The fields and current densities induced by a split classic coil with the surface unconnected showed the largest deviation from those given by the conventional non-split coils. Another finding indicated that the distributions of the peak current densities varied when the body position, orientation or gender changed, while the peak electric fields mainly occurred in the skin and fat tissues.
磁共振引导直线加速器(MRI-LINAC)是一种新型的图像引导放射治疗系统,它将磁共振成像(MRI)与直线加速器(LINAC)集成在一个单元中。其缺点之一是,系统分裂梯度线圈的脉冲会在患者体内产生电场和电流,需要对其进行预测和评估以确保患者安全。在这项新的数值研究中,当使用多种不同的分裂几何梯度线圈时,评估了位于 MRI-LINAC 系统中的组织精确的男性和女性人体体素模型内部的原位电场和相关电流密度。体模沿着轴向和径向方向放置在三个不同的体位中。每个模型都有一个适合图像引导放射治疗的感兴趣区域(ROI)。模拟结果表明,在体模 ROI 中,不同分裂 x 梯度线圈产生的场和电流密度的幅度和分布彼此相似,但在区域之外则有所不同。表面未连接的分裂经典线圈产生的场和电流密度与传统的非分裂线圈有较大的偏差。另一个发现表明,当体位、方位或性别改变时,峰值电流密度的分布会发生变化,而峰值电场主要出现在皮肤和脂肪组织中。