CyberKnife系统中肝癌计划实施剂量计算及验证的评价研究

Evaluation of Dose Calculation and Verfication Plan of Liver Cancer in CyberKnife

目的采用Monte Carlo与Ray-Tracing算法实施剂量计算及验证,分析和评估肝癌典型病例CyberKnife计划的准确性、可靠性,为不同算法在临床应用中的选择提供参考。方法选择在我科行CK治疗的肝癌肿瘤患者33例,分别使用射线追踪(Ray-Tracing,RT)算法和蒙特卡罗(Monte Carlo,MC)算法进行计划剂量计算并评估;另从中选取10例用固体水模对计划进行剂量验证。结果左叶肝癌靶区RT算法的平均剂量值为58.21 Gy,MC算法的平均值为57.76,两者相差0.45 Gy(0.78%);右叶肝癌RT算法的平均值为55.82 Gy,MC算法的平均值为54.60 Gy,两者相差1.22 Gy(2.23%);采用MC算法重新精算后,食管、胃、脊髓、肠道、十二指肠及肝脏的平均剂量均有所降低,差异有统计学意义(P<0.05);以MC算法剂量计算作为基准,肝癌患者中RT算法高估1.09%,差异有统计学意义(P<0.05);采用均匀固体水进行验证,RT和MC两种算法点剂量计算值与测量值差异均在±3%以内,采用3%/2 mm标准分析γ通过率均大于93%。结论本研究通过对RT和MC两种算法在肝癌肿瘤实施计划剂量计算及其验证开展了系统研究与测试,对其准确性及偏差进行了考证,可为CK系统中肝癌计划算法的选择和治疗实施提供依据,对临床具有一定的指导意义。

Objective In this study,different algorithms were used for dose calculation and verification of SRT plans in typical cases of liver cancer.The accuracy and reliability of SRT plans under different conditions were analyzed and evaluated,so as to provide certain reference for the selection of different algorithms in clinical application.Methods In this study,33 liver cancer patients treated with CK in our department were chosen.The dose calculation and verification were done to evaluate using Ray-Tracing(RT)and Monte Carlo(MC)algorithms respectively.In addition,10 typical cases were selected to do the dose verificaiton with solid water.The differences between the two algorithms and its selection of application were analyzed and discussed.Results The average dose value of RT algorithm in the target area of left lobe liver cancer was 58.21 Gy,and the average value of MC algorithm was 57.76.The difference between two algorithms was 0.45 Gy(0.78%).The mean value of RT algorithm in right lobe liver cancer was 55.82 Gy,and the average value of MC algorithm was 54.60 Gy,with a difference of 1.22 Gy(2.23%).After re-calculation using MC algorithm,the average dose of esophagus,stomach,spinal cord,intestinal tract,duodenum and liver were all decreased,with statistical significance(P<0.05).Taking the dose calculation of MC algorithm as the baseline,RT algorithm was overestimated by 1.09% in patients with liver cancer,and the difference was statistically significant(P<0.05).Uniform solid water was used for verification,the difference between the calculated value of point dose and the measured value of RT and MC was within ±3%,and the passing rate of γ analysis using 3%/2 mm standard was greater than 93%.Conclusion In this study,the systematic research and measurement were carried out on dose calculation and verification of the RT and MC algorithms in liver tumor sites,and their accuracy and deviation were verified,thus providing the basis for the selection and treatment implementation of SRT plans in liver sites of CK system,which has a certain guiding significance for clinical practice.