Karaiskos P, Angelopoulos A, Sakelliou L, Sandilos P, Antypas C, Vlachos L, Koutsouveli E
Physics Department, University of Athens, Greece.
Med Phys. 1998 Oct;25(10):1975-84. doi: 10.1118/1.598371.
An analytical Monte Carlo simulation code has been used to perform dosimetry calculations around an 192Ir high dose-rate brachytherapy source utilized in the widely used microSelectron afterloaded system. Radial dose functions, dose rate constant and anisotropy functions, utilized in the AAPM Task Group 43 dose estimation formalism, have been calculated. In addition, measurements of anisotropy functions using LiF TLD-100 rods have been performed in a polystyrene phantom to support our Monte Carlo calculations. The energy dependence of LiF TLD response was investigated over the whole range of measurement distances and angles. TLD measurements and Monte Carlo calculations are in agreement to each other and agree with published data. The influence of phantom dimensions on calculations was also investigated. Radial dose functions were found to depend significantly on phantom dimensions at radial distances near phantom edges. Deviations of up to 25% are observed at these distances due to the lack of full scattering conditions, indicating that body dimensions should be taken into account in treatment planning when the absorbed dose is calculated near body edges. On the other hand, anisotropy functions do not demonstrate a strong dependence on phantom dimensions. However, these functions depend on radial distance at angles close to the longitudinal axis of the source, where deviations of up to 20% are observed.
已使用一种分析型蒙特卡罗模拟代码，对广泛使用的微型后装系统中所采用的¹⁹²Ir高剂量率近距离放射治疗源周围进行剂量学计算。已计算出美国医学物理师协会任务组43剂量估算形式中所使用的径向剂量函数、剂量率常数和各向异性函数。此外，已在聚苯乙烯模体中使用LiF TLD - 100棒对各向异性函数进行测量，以支持我们的蒙特卡罗计算。在整个测量距离和角度范围内研究了LiF TLD响应的能量依赖性。TLD测量结果与蒙特卡罗计算结果相互吻合，且与已发表的数据一致。还研究了模体尺寸对计算的影响。发现在靠近模体边缘的径向距离处，径向剂量函数显著依赖于模体尺寸。由于缺乏完全散射条件，在这些距离处观察到高达25%的偏差，这表明在靠近身体边缘计算吸收剂量时，治疗计划中应考虑身体尺寸。另一方面，各向异性函数并未表现出对模体尺寸的强烈依赖性。然而，这些函数在靠近源纵轴的角度处依赖于径向距离，在这些角度处观察到高达20%的偏差。
