电子射野影像系统在测量调强放疗三维剂量上的应用

目的:采用三维γ分析与靶区平均剂量评估电子射野影像系统(electronic portal imaging device,EPID)在测量调强放疗三维剂量上的应用特点.方法:首先在固体水模体中测试规则野和调强野,分析点剂量、平面γ通过率及靶区三维γ通过率的模型重建精度;再采用EPID测量80例鼻咽癌患者调强放射治疗(i...

Electronic Portal Imaging Devices in 3D Dose Measurement for Intensity Modulated Radiotherapy

Objective:To evaluate the application of electronic portal imaging devices(EPID)in 3D dose measurement for intensity modulated radiation therapy(IMRT)by 3D 7 analysis and average target dose.Methods:Regular fields and IMRT fields were first tested in the solid water phantom to analyze the model reconstruction accuracy of point dose,planar γ pass rate and 3D γ pass rate of targets.EPID was then used to measure IMRT in 80 patients with nasopharyngeal carcinoma.3D γ pass rates and average doses were analyzed based on 3D dose before CT reconstruction.12 cases were finally selected to analyze the effect of cavity correction on 3D γ pass rates and target doses.Results:The average isodose deviation of 3D dose reconstruction for IMRT in solid water phantom was-1.09%±1.27%;the 2D y pass rate was 99.38%;and the 3D γ pass rate of planning target volume(PTV)was 98.01%.For the 80 nasopharyngeal carcinoma patients undergoing CT reconstruction,3D γ pass rates of PTV with 3%/3 mm and 5%/3 mm criteria were 89.71%±5.71%and 96.36%±3.02%,respectively.The 7 pass rates(3%/3 mm)of PTV1 and the gross tumor volume of nasopharynx in 12 cases were 91.20%±3.53%and 87.70%±8.07%before cavity correction;and they became 96.80%±2.15%and 97.9%±3.41%after cavity correction;There were statistically significant differences before and after the correction(t=-7.214,P<0.001=-4.263=0.001).The average dose deviation before and after reconstruction were 0.70%±1.30%and 0.60%±2.05%;and the difference was not significant(t=-1.910,P=0.083;t=1.083=0.302).Conclusion:3D y analysis is reliable in quality assurance for 3D dose verification.Cavity correction could improve 3D γ pass rates of the target,but has litde effect on the average dose.The analysis and evaluation of the average dose of the target is clinically applicable and valuable for 3D dose verification.