Small Volume Ionization Chambers Angular Dependence and Its Influence on Point-Dose Measurements
Small Volume Ionization Chambers Angular Dependence and Its Influence on Point-Dose Measurements
复制标题
小体积电离室角度依赖性及其对点剂量测量的影响
DOI：
10.4236/ijmpcero.2016.51003
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
I. Orion
中科院分区：
文献类型：
--
作者：
J. Feldman;I. Orion
目的：作为PinPoint和CC01的圆柱形电离室具有高空间分辨率和与小场相关的圆柱形对称性。在包括非共面光束在内的最新先进技术中，如伽玛刀、VMAT和IMRT治疗计划中，离子室的角度依赖性是必不可少的。因此，在本研究中，我们使用蒙特卡罗方法模拟了两个常用的离子室。方法：计算了6 MV和15 MV两束LINAC光子光束在圆柱形水影中较大角度范围内CC01和PinPoint的角依赖性。为了揭示在医疗应用中高于2%的不对称响应剂量，使用蒙特卡罗代码对每个离子室进行了完整的结构描述计算。计算出的CC01离子室的剂量响应，通过测量得到了验证。结果：与PinPoint离子室相比，CC01离子室的角度依赖性很小。在0°~ 110°范围内，其相对角依赖幅度约为12%。结论：离子室结构的不同导致了相对角依赖性振幅的变化。因此，在选择探测器时，不仅要考虑电离室的体积，还要考虑电离室的结构。
Purpose: Cylindrical ionization chambers as the PinPoint and the CC01 have high-spatial resolution and cylindrical symmetry in relevance to small fields. Dosimetry of newly advanced technologies that include non-coplanar beams, such as in Gamma-Knife, VMAT and IMRT treatment plans, the angular dependence of the ion chamber is essential. Therefore in this study we simulated two common used ion chambers using a Monte Carlo method. Methods: The angular dependence for the CC01 and the PinPoint were calculated for a vast angular range in a cylindrical water phantom for two LINAC photon beams, 6 MV and 15 MV. The calculations were performed for fully structural description of each ion chamber using Monte Carlo code, in order to reveal unsymmetrical response dose higher than 2% in medical applications. The calculated dose response, for the CC01 ion chamber, was validated with measurements. Results: The CC01 ion chamber showed a very small angular dependence compared to the PinPoint ion chamber. The relative angular dependence amplitude of the PinPoint was about 12% in the range of 0° - 110°. Conclusions: The differences in the ion chambers structure led to the variations in the relative angular dependence amplitude. Therefore, when choosing a detector, not only the volume of the ionization chamber but also its structure must be taken into consideration.