高剂量率^(192)Irγ射线参考辐射场的搭建

Construction of High Dose Rate^(192)Irγ-rays Reference Radiation Field

为完成高剂量率^(192)Ir放射源参考空气比释动能率的绝对测量工作,设计了专用的辐照器及定位装置,利用医用高剂量率近距离治疗机搭建了准直的参考辐射场。参考ISO 4037等相关标准,对参考辐射场的散射、辐射野、半值层、有效能量等相关参数进行了测量和研究。结果显示,在辐射场多个位置,环境散射份额小于主射束的0.003%;在距离放射源1.4 m的位置,辐射野直径为98 mm,尺寸大于基准石墨空腔电离室;半值层测量结果为8.224 mm(Cu),有效能量为402.8 keV,利用HPGe探测器测量的^(192)Ir能谱与模拟谱契合度良好。各项参数均满足了^(192)Ir近距离治疗源参考空气比释动能率的量值复现要求,为其绝对测量与国际比对工作打下基础。

To complete the absolute measurement of the reference air kerma rate of the high dose rate^(192)Ir radioactive source,a special irradiator and positioning device was designed,and a collimated reference radiation field was built using a medical high dose rate brachytherapy machine.Concerning relevant standards such as ISO 4037,the scattering,radiation field,half-value layer,effective energy and other related parameters of the reference radiation field were measured.The results show that the ambient scattering share is less than 0.003%of the main beam at multiple locations in the radiation field;at a distance of 1.4 m from the radiation source,the diameter of the radiation field is 98 mm,which is larger than the benchmark graphite cavity ionization chamber;the layer measurement result is Cu of 8.224 mm,and the effective energy is 402.8 keV.The^(192)Ir energy spectrum measured by HPGe detector is in good agreement with the simulated spectrum.All the parameters met the requirement of the^(192)Ir brachytherapy source reference air kerma rate to reproduce the magnitude,which laid the foundation for its absolute measurement and international comparison.