基于蒙特卡罗数学模型评价不同螺距冠状动脉CCTA受检者辐射剂量的特点与验证

Estimation and validation of radiation dose to patients subjected to high-pitch and standard-pitch CCTA using Monte Carlo software

收集61例采用双源CT Flash大螺距冠状动脉CCTA(Coronary Computed Tomography Angiography,CCTA)受检者资料,按WHO亚洲人体质量指数(BMI)标准将研究对象分为三组:正常组(12例)、超重组(41例)和肥胖组(8例),应用蒙特卡罗(Monte Carlo)数学模型软件计算三组受检者大螺距与常规螺距行CCTA的器官剂量,比较两种螺距CCTA时受检者的器官剂量分布特点及两种螺距CCTA的有效剂量变化幅度,并与大螺距模式下CT设备直接读取法所得有效剂量值进行比较。结果表明,用蒙特卡罗软件计算的双源CT大螺距CCTA受检者的器官剂量比常规螺距技术的剂量降低约70%,其中心脏、胸腺的器官剂量下降最为明显,降幅最大约80%;三组CCTA受检者大螺距较常规螺距的有效剂量(E)均降低明显(p<0.05),正常组使用大螺距技术后有效剂量E降幅最为明显;大螺距模式下数学模型软件模拟有效剂量E与CT设备所测有效剂量E间的偏差度小于50%。说明Monte Carlo数学模型软件可用于检查前预估或回顾性分析CCTA扫描时受检者的器官剂量与有效剂量的分布情况,并预判CCTA大螺距模式对受检者的胸部器官剂量和有效剂量,从而达到了降低辐射剂量的目的,尤其对BMI较小的受检者(如儿童)控制辐射风险更具意义。对开展低剂量CT技术具有一定实际意义。

The distribution characteristics of radiation dose of Coronary Computed Tomography Angiography（CCTA） with high-pitch and standard-pitch is studied using Monte Carlo simulation. The data from 61 patients subjected to high-pitch CCTA using the dual source CT scanner were collected and divided into 3 groups according to the BMI classification for Asians recommended by WHO： normal group（12 cases）,overweight group（41 cases） and obese group（8 cases）. Organ dose and effective dose（E） of the three groups with highpitch and standard-pitch CCTA were calculated using Monte Carlo software. In high-pitch mode,the effective dose values calculated by Monte Carlo software were compared with the direct data readings from the CT equipment. The results showed that the organ dose of high-pitch CCTA calculated by the Monte Carlo software was about 70% lower than that of standard-pitch CCTA on the dual source spiral CT. The most significant reductions in organ doses were found for heart and thymus,which have decreased by about 80%. For all the 3groups,the effective doses of high-pitch CCTA were significantly lower than those of the standard-pitch CCTA（p 0. 05）,and the most obvious reduction in E was found in patients of the normal group subjected to the high-pitch CCTA. In high-pitch mode,deviation in E between the Monte Carlo simulation and the reading of the CT device was less than 50%. This suggested that,as a new clinical calculation method for radiation dose,Monte Carlo simulation can be used for prediction or retrospective analysis of the distribution of organ dose and E in CCTA. It is also indicated that the chest organ dose and effective dose can be significantly reduced with the high-pitch CCTA,and this will subsequently decrease the radiation risk,especially for the subjects of smaller BMI（such as children）. This study has a potential for practical applications in development of low dose CT technology.