食管癌图形引导的放射治疗(IGRT)6个自由度摆位误差研究

目的 肿瘤患者在接受放射治疗的过程中,会因各种原因引起摆位误差,影响放射治疗的准确性.因此有必要利用锥形束CT在线研究食管癌六个自由度的摆位误差,为临床提供数据.方法 采用图像引导的放射治疗(imageg uidedr adiotherapy,IGRT) 的锥形束CT(cone-beam computed tomography,CBCT)影像技术获得患者左右(X)、头脚(Y)、前后(Z)3个方向的线性摆位误差以及分别以X、Y、Z轴旋转形成相应的U、V、W旋转摆位误差.对食管癌患者146次治疗前摆位后、摆位误差调整后及治疗后获取348个CBCT信息,通过系统配有的匹配功能,获取的CBCT 图像与计划CT 图像相匹配,获取线性误差和旋转误差,分析其摆位误差.结果 将计划CT作为参考标准,治疗前摆位后的摆位误差呈近似正态分布,系统误差(均数)±随机误差(标准差)在X、Y、Z、U、V、W6个自由度分别为(0.85±3.56)mm、(1.82±4.00)mm、(-2.31±2.10)mm、(0.59±0.85)°、(0.29±1.30)°、(0.40±0.86)°.误差调整后再次CBCT,结果 显示摆位误差明显缩小 (P＜0.05).结论 食管癌放射治疗摆位误差在Y、Z方向上较为明显,个别患者还有较大的旋转误差,通过CBCT测量食管癌患者治疗前的摆位误差,并行6个自由度的在线调整误差,可明显减小平面误差和旋转误差,提高放疗准确性.

Study of 6-D setup error in IGRT on esophageal carcinoma

Objective When patients are in radiotherapy,setup errors are unavoidable which may affect the precision for radiotherapy.This study was to analyze the setup errors in radiotherapy on esophageal cancer.Methods Translational errors (X,Y,and Z) and rotational errors (U,V and W) were obtained by using cone-beam computed tomography (CBCT) in radiotherapy.Patients received a total of 348 CBCT scans after initial setup,re-positioning and radiation delivery.The CBCT images were registered to the planning CT images,and then the setup errors on X,Y,Z,U,V and W degrees were analyzed.Results Setup errors were normal distribution.The systemic±random errors on X,Y,Z,U,V and W axes were (0.85±3.56)mm,(1.82±4.00)mm,(-2.31±2.10)mm,(0.59±0.85)°,(0.29±1.30)° and (0.40±0.86)°,respectively.Comparing the initial setup errors,the re-positioning setup errors decreased significantly on all the six axes (P＜0.05).Conclusion s The setup errors in Y and Z degree are more obviously,while some biggish setup errors exist in rotational errors.Measurement and correction of setup errors before each fraction by using CBCT could help to improve the precision for radiotherapy.