鼻咽癌调强放疗摆位误差对剂量分布影响的研究

目的探讨鼻咽癌（NPC）调强放射治疗（IMRT）中摆位误差对靶区和危及器官物理剂量的影响。方法对6例鼻咽癌患者,应用瓦里安Trilogy直线加速器的机载影像系统（On-Borad-Imager）,实时采集CBCT图像,治疗前行CT扫描取得实际图像,将CBCT图像与计划系统的模拟定位CT图像靶中心匹配。采用瓦里安专用的分析软件计算x（左右）、y（头脚）、z（腹背）方向偏移误差,并通过Eclipse 8.6 Version治疗计划系统研究误差在鼻咽癌放疗中对剂量分布的影响。结果系统误差（均差mean）±随机误差（标准差stdev）在x、y、z方向分别为（-0.52±1.2）mm、（-0.22±2.54）mm、（-0.53±1.21）mm,颈部转移淋巴结（GTVnd）总剂量分布变化为0.32%～12.34%,鼻咽原发肿瘤（GTVnx）剂量变化为-0.25%～0.32%,左晶体剂量变化为-12.45%～0.13%,右晶体剂量变化为-17.87%～-0.08%,脊髓剂量变化为-0.18%～8.20%,脑干剂量变化为-5.40%～6.55%。结论鼻咽癌IMRT摆位误差是难以避免的,应用OBI-CBCT系统,进行实时摆位误差校正,尽可能减少系统误差和随机误差,提高摆位精度,使靶区及周围正常组织器官剂量分布准确,为临床放疗提供质量保证。

Effects of the Setup Error on the Dose Distribution for Nasopharyngeal Carcinoma with Intensity Modulated Radiation Therapy

Objective To evaluate the effect of the setup error on the physics dose distribution of targets and peripheral organs at risk（OAR） undergoing the intensity modulated radiation therapy for nasopharyngeal carcinoma（NPC）.Methods Six NPC patients were included into our study.The On-Borad-Imager of Varian Trilogy linear accelerator was used to collect the images of Cone Beam Computerized Tomography（CBCT） in real time,which were matched with the positioning CT images before radiation treatment through target center.The Varian software was used to calculate the error in x（left-right）,y（cranial-caudal） and z（ventral-dorsal） direction.Then the treatment planning system of Eclipse8.6Version was used to study the effects of the setup error on the dose distribution undergoing the radiation therapy for NPC.Results The systematic±random error in x,y,and z direction was（-0.52±1.20）mm,（-0.22±2.54）mm and（-0.53±1.21）mm,respectively.The extent of dose variation for GTVnd,GTVnx,left lens,right lens,spinal cord,and brainstem was 0.32%～12.34%,-0.25%～0.32%,-12.45%～0.13%,-17.87%～-0.08%,-0.18%～8.20% and-5.40%～6.55%.Conclusion The setup errors were inevitable in radiation therapy.However,the OBI-CBCT system could revise the setup error in real time,which could reduce the systematic and random error and improve the accuracy of setup and dose of targets and OAR.As a result,it could provide better quality assurance in radiation therapy.