基于新型空气等效材料的治疗水平电离室研究

Research of the new air-equivalent material ionization chamber dosimeters used in radiotherapy

针对目前使用的治疗水平电离室石墨帽有效原子序数偏低,且易碎等问题,研究以空气电子密度、等效原子序数、反应截面为基础,模拟计算出空气等效材料的有效原子权重及质量配比。采用高纯石墨烯粉末作为基材,添加纯度为99.9%的偏氟材料,高温融化搅拌高压压制成空气等效板材,该材料导电率为0.03 S/cm,质量密度为1.8 g/cm^3。以该空气等效板材为基础,设计加工一种新型的0.6 cm^3治疗水平电离室,并采用不同材质的收集极做能响实验,确定收集极的材质。通过实验证明,该电离室漏电(零点漂移)为0.15%,测量重复性为0.07%,示值非线性为0.27%,X能量响应为1.63%,X/γ能量响应为-0.48%,杆旋转为0.46%,满足JJG 912——2010《治疗水平电离室剂量计》对电离室的要求。

The current the graphite cap of ionization chamber used in radiotherapy has low effective atomic number and is fragile. The effective atomic weight and mass ratio of air equivalent materials were simulated and calculated based on air electron density, equivalent atomic number and reaction cross section. High purity graphene powder was used as base materials and partial fluorine material with purity being 99.9% was added to manufacture air equivalent sheets via high temperature melting and stirring under high pressure conditions. Its conductivity is 0.03 S/cm and mass density is 1.8 g/cm3. A new type of 0.6 cm3 ionization chamber for radiotherapy made on the base material of air equivalent sheets was designed and processed and collectors made of different materials were used to carry out energy response, so as to determine the material of collectors. The test shows that the ionization chamber power leakage （zero drift） is 0.15%, the measurement repeatability is 0.07%, the indication nonlinearity is 0.27%, the X energy response is 1.63%, the X/~ energy response is -0.48% and the rod rotation is 0.d6%, meeting the requirements of Ionization Chamber Dosimeters Used In Radiotherapy（JJG 912 2010） on ionization chamber.