Fuchs Hermann, Padilla-Cabal Fatima, Hummel Andreas, Georg Dietmar
Division of Medical Radiation Physics, Department of Radiation Oncology, Medical University of Vienna, Währinger Gürtel 18-20, Wien, 1090, Austria.
Med Phys. 2021 Jan;48(1):505-512. doi: 10.1002/mp.14605. Epub 2020 Dec 8.
To design and commission a water phantom suitable for constrained environments and magnetic fields for magnetic resonance (MR)-guided proton therapy.
A phantom was designed, to enable precise, remote controlled detector positioning in water within the constrained environment of a magnet for MR-guided proton therapy. The phantom consists of a PMMA enclosure whose outer dimensions of were chosen to optimize space usage inside the 13.5-cm bore gap of the magnet. The moving mechanism is based on a low-height H-shaped non-ferromagnetic belt drive, driven by stepper motors located outside of the magnetic field. The control system and the associated electronics were designed in house, with similar features as available in commercial water phantoms. Reproducibility as well as accuracy of the phantom positioning were tested using a high-precision Leica AT 402 laser tracker. Laterally integrated depth dose curves and lateral beam profiles at three depths were acquired repeatedly for a 148.2 MeV proton beam in water.
The phantom was successfully operated with and without applied magnetic fields. For complex movements, a positioning uncertainty within 0.16 mm was found with an absolute accuracy typically below 0.3 mm. Laterally integrated depth dose curves agreed within 0.1 mm with data taken using a commercial water phantom. The lateral beam offset determined from beam profile measurements agreed well with data from Monte Carlo simulations.
The phantom is optimally suited for detector positioning and dosimetric experiments within constrained environments in high magnetic fields.
设计并调试一种适用于受限环境和磁场的水模体，用于磁共振（MR）引导的质子治疗。
设计了一种模体，以便在MR引导质子治疗的磁体受限环境中，能够在水中进行精确的远程控制探测器定位。该模体由一个聚甲基丙烯酸甲酯外壳组成，其外部尺寸经过选择，以优化磁体13.5厘米孔径间隙内的空间使用。移动机构基于低高度H形非铁磁带传动，由位于磁场外部的步进电机驱动。控制系统及相关电子设备是内部设计的，具有与商用含水模体类似的功能。使用高精度徕卡AT 402激光跟踪仪测试了模体定位的再现性和准确性。对于148.2兆电子伏特质子束在水中的情况，重复获取了三个深度处的横向积分深度剂量曲线和横向射束轮廓。
该模体在施加和未施加磁场的情况下均成功运行。对于复杂运动，定位不确定度在0.16毫米以内，绝对精度通常低于0.3毫米。横向积分深度剂量曲线与使用商用含水模体获取的数据在0.1毫米范围内一致。从射束轮廓测量确定的横向射束偏移与蒙特卡罗模拟数据吻合良好。
该模体最适合在高磁场的受限环境中进行探测器定位和剂量测定实验。
