放疗中二维平板电离室阵列所测剂量的空间映射研究

二维平板电离室阵列常用于临床放疗的剂量分布探测，其所测剂量实际对应的空间位置（即有效测量点或剂量-空间位置对应关系）是精确放疗中需研究的重要问题。本文采用蒙特卡罗方法研究了用于放疗剂量分布监测的二维平板电离室阵列的有效测量点位置及其随电离室的空腔直径、空腔厚度和射线能量等的变化规律。先用蒙特卡罗模拟得到水模体在MeV级光子束辐照下射野中心轴上的剂量曲线，再在相同条件下模拟获得二维平板电离室阵列测得的剂量曲线，然后通过相关性分析，得到有效测量点。结果表明，用于放疗的二维平板电离室阵列的有效测量点相对于前表面中心有一小于1 mm的偏移；该偏移量随电离室空腔厚度、射线能量的增加而增加，随电离室空腔直径的增加而减小。

Dose-space Mapping Study on 2D Ion-chamber Array in Radiotherapy

The 2D ion‐chamber array is widely used in dose distribution measurement in radiotherapy ,and its effective point of measurement (EPOM ) ,i .e .the accurate dose‐space mapping position related to the dose from ion‐chamber ,is an important problem in accurate radiotherapy . In this study , Monte Carlo simulations were employed to research the EPOM for 2D ion‐chamber array .Both the actual dose distribution along the central axis of photon beam in a water phantom in the absence of the probe and the dose curve from 2D ion‐chamber array were simulated to locate the position of the EPOM by correlation analysis .It is found that the EPOM for 2D ion‐chamber array is shifted from the front face of the ion‐chamber cavity toward the cavity center by less than 1 mm .And the EPOM depends on the ion‐chamber layout and the beam character‐istics .The EPOM shift increases with the length of the cavity and the energy of the beam ,and decreases with the increase of the cavity diameter .