Experimental verification of magnetic field dose effects for the MRI-accelerator
Experimental verification of magnetic field dose effects for the MRI-accelerator
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DOI：
10.1088/0031-9155/52/14/017
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发表时间：
2007-07-21
影响因子：
3.5
通讯作者：
Lagendijk, J. J. W.
中科院分区：
文献类型：
--
作者：
Raaijmakers, A. J. E.;Raaymakers, B. W.;Lagendijk, J. J. W.
目前正在开发的MRI直线加速器系统设计为在磁场存在下对患者进行辐照。由于洛伦兹力作用于二次电子，这影响了剂量分布。模拟表明，发生以下剂量效应：积聚距离减小，横向轮廓在与磁场正交的方向上变得不对称，并且在组织-空气界面处，由于返回电子，剂量增加。在这项工作中，GafChromic薄膜测量在磁场的存在下进行实验量化这些剂量效应。在PMMA -空气- PMMA体模中测量深度-剂量曲线，并在均匀PMMA体模中测量侧向轮廓，光子束突出体模边缘。测量结果证实了模拟预测的磁场剂量效应。这使我们能够验证这些MRI直线加速器特定剂量效应的Geant 4 Monte Carlo模拟：测量和模拟之间的深度-剂量曲线的相对一致性在2.2%/1.8 mm内。侧向轮廓的相对一致性为2.3%/1.7 mm。总的来说，可以在测量精度内使用Geant 4蒙特卡罗模拟来模拟利用MRI直线加速器辐照所预期的磁场剂量效应。
The MRI-linear accelerator system, currently being developed, is designed such that the patient is irradiated in the presence of a magnetic field. This influences the dose distribution due to the Lorentz force working on the secondary electrons. Simulations have shown that the following dose effects occur: the build-up distance is reduced, the lateral profile becomes asymmetric in the direction orthogonal to the magnetic field and at tissue - air interfaces the dose increases due to returning electrons. In this work, GafChromic film measurements were performed in the presence of a magnetic field to experimentally quantify these dose effects. Depth - dose curves were measured in a PMMA - air - PMMA phantom and the lateral profiles were measured in a homogeneous PMMA phantom with the photon beam protruding over the edges of the phantom. The measurement results confirmed the magnetic field dose effects that were predicted by simulations. This enabled us to verify Geant4 Monte Carlo simulations of these MRI-linac specific dose effects: the relative agreement for the depth - dose curves between measurements and simulations was within 2.2%/1.8 mm. The relative agreement for the lateral profiles was 2.3%/1.7 mm. Overall, the magnetic field dose effects that are expected for irradiation with the MRI-linac can be modelled using Geant4 Monte Carlo simulations within measurement accuracy.