15MeV医用电子直线加速器治疗室内光核中子辐射场的研究

Research on Photo Neutron Radiation Field Inside Therapy Room for 15 MeV X-Ray Medical Linear Accelerator

医用电子直线加速器产生的X射线已广泛的应用于放射治疗过程。由于X射线能量高于某一阈值与周围物质发生(γ,n),(γ,2n)反应而产生光核中子,导致治疗过程中,存在一定程度的中子污染危害。采用Monte-Carlo模拟方法,以点源模型对一台工作在15MeV能量档的Primμs-M型医用电子直线加速器,对照射野在0cm×0cm、3cm×3cm、5cm×5cm、10cm×10cm和20cm×20cm时,使用CR-39固体核径迹探测器和中子气泡探测器(BND)对照射野及照射野外中子剂量分布进行了测量,并对光中子剂量分布进行了模拟。测量和模拟的结果均表明,单一照射野内,光核中子引起的剂量随照射野周长减少呈指数增强趋势。随着照射野面积增大,光核中子总注量逐步增强。采用调强适形放射治疗时,光核中子引起的中子剂量贡献不容忽视。

X-ray produced by medical accelerator has been widely used in radiotherapy.During the process of therapy,a certain level of neutron contamination was induced due to the interaction （γ,n）,（γ,2n）happening between X-ray and substances surrounded.The neutron dose distributions caused by a medical accelerator working at 15 MeV mode at the exposure field of 0 cm×0 cm,3 cm×3 cm,5 cm×5 cm,10 cm×10 cm and 20 cm×20 cm were simulated in the model of point source by Monte-Carlo respectively,and measurements of neutron dose distribution inside and outside the exposure field were carried out by CR-39 solid state nuclear track detector and bubble neutron detector （BND）.The results of both simulation and measurement show that neutron dose presents an increasing trend following the decrease of circumference of exposure field.Therefore,enough attention should be paid to the contribution of neutron dose during the intensive modulated radiotherapy.