MRI引导放射治疗中电子回转效应的蒙特卡罗研究
Study on the Electronic Return Effect in the MRI Guided Radiotherapy by Monte Carlo Simulation
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摘要: 为了研究磁共振引导放射治疗对剂量分布的影响，采用蒙特卡罗方法研究了横向均匀磁场对6 MV光子束在4种不同人体组织材料与空气界面处因电子回转效应导致剂量分布的改变。模拟显示，对于电离能相近的几种材料，磁场对剂量分布扰动的差别较小，而且电离能较大的材料，这种扰动明显变小。结果表明，磁场的引入会影响光子束原有的剂量分布，且这种影响与材料的电离能有关。这意味着虽然磁共振引导放射治疗可以增强靶向精度，提高治疗效果，但磁场会导致光子束剂量分布的改变，且不同的组织这种改变也不相同，这将为相应的剂量算法研究带来了新的挑战。A Monte Carlo code was used to study the discrepancy resulted from the emergence of magnetic field in MRI guided radiotherapy. In this work, four different tissue phantoms with magnetic field and 6 MV photon were studied, and the dose distributions at the interface of phantom-air were evaluated. It is found that the differences of the dose perturbation are small between the materials with similar ionization energy. However, the dose perturbation decreased significantly for the material with high ionization energy. The results of this study demonstrate that magnetic field will change the dose distribution of photon beam and the dose perturbation associated with ionization energy of materials. It means that magnetic resonance imaging guided radiotherapy can enhance the target accuracy, but the magnetic field will change the dose distribution of photon beam, and the perturbation was not the same for the different materials of human tissue, it has brought new challenges for the research of dose algorithm.Abstract: A Monte Carlo code was used to study the discrepancy resulted from the emergence of magnetic field in MRI guided radiotherapy. In this work, four different tissue phantoms with magnetic field and 6 MV photon were studied, and the dose distributions at the interface of phantom-air were evaluated. It is found that the differences of the dose perturbation are small between the materials with similar ionization energy. However, the dose perturbation decreased significantly for the material with high ionization energy. The results of this study demonstrate that magnetic field will change the dose distribution of photon beam and the dose perturbation associated with ionization energy of materials. It means that magnetic resonance imaging guided radiotherapy can enhance the target accuracy, but the magnetic field will change the dose distribution of photon beam, and the perturbation was not the same for the different materials of human tissue, it has brought new challenges for the research of dose algorithm.
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