基于EGSnrc仿真的二维电离室剂量探测器的室壁厚度确定方法

室壁厚度是二维电离室剂量探测器的重要设计参数。在二维电离室剂量探测器的单元空腔几何参数确定的情况下，利用蒙特卡罗仿真方法建立了探测器室壁仿真计算的简化模型，并利用EGSnrc程序对模型进行了仿真计算，给出了室壁厚度的参考数值。结果表明，当空腔为直径4.5 mm、高5 mm的圆柱形时，在能量为1.25 MeV射线下，为达到1%的测量精度，电离室前壁厚度需达到4.4 mm，侧壁厚度需达到1.5 mm；在1.25~4 MeV射线能量范围内使用时，为达到1%的测量精度，侧壁厚度需达到5 mm。本文研究结果可作为该种探测器的设计依据。

Method on Determination of Wall-thickness of Two-dimensional Ionization Chamber Dose Detector Based on EGSnrc

The wall-thickness is an important design parameter for two-dimensional ionization chamber dose detector. Under the given geometric parameters of the cavity unit of two-dimensional ionization chamber dose detector, the simulation model was built by using Monte Carlo method. The wall-thickness was calculated with the simulation model using EGSnrc, and the reference numerical value was given. The result shows that when the cavity is a cylinder with diameter of 4.5 mm and height of 5 mm, under radiation of 1.25 MeV, the front wall-thickness of ionization chamber should be more than 4.4 mm and the side wall-thickness should be 1.5 mm in order to meet the demand of accuracy of 1%. Under the radiation with energy of 1.25-4 MeV, the side wall thickness should be more than 5 mm in order to meet the demand of accuracy of 1%. The research result can be used as the design basis for the detector.