应用锥形束CT对宫颈癌及子宫内膜癌术后放疗立置误差的研究

The setup errors in postoperative radiotherapy for endometrial and cervical cancer by cone beam CT

目的 通过对宫颈癌及子宫内膜癌术后放射治疗患者位置误差的分析,确定临床靶区（CTV）外扩计划靶区（PTV）边界值的大小.方法 选取26例宫颈癌及子宫内膜癌术后放疗患者通过千伏级锥形束CT（kV-CBCT）采集初次治疗前和以后每周的CT影像,与治疗计划采用的CT影像进行比对,记录各方向位置误差值并计算PTV外扩边界值M PTV.结果 宫颈癌及子宫内膜癌术后患者放疗时各方向均存在位置误差,患者在左右、头脚和前后方向误差分别为（0.21 ±3.23）、（0.55±3.51）和（0.08±2.76）mm,头脚方向的系统误差最大,左右方向次之、前后方向最小.各方向位置误差无明显差异.靶区在左右、头脚和前后方向依次需外扩5.44、7.26和5.68 mm.结论建议在进行宫颈癌及子宫内膜癌术后放疗时外扩PTV间距依次为左右方向5.5 mm、头脚方向7.5 mm、前后方向6 mm.

Objective To analyze the setup errors in postoperative radiotherapy for endometrial and cervical cancer and to determine the margin required for clinical target volume （CTV） extending to planning target volume （PTV） （MPTV）.Methods The setup errors of 26 endometrial and cervical cancer patients receiving postoperative radiotherapy from April to June 2013 were measured and analyzed in this study.Linear errors（x,y,z axis） were obtained by cone beam CT （CBCT）.MPTV were determined.Results Setup errors were unavoidable in postoperative endometrial and cervical cancer irradiation.The setup errors（systemic ± random） on x （left-right）,y （superior-inferior）,z （anterior-posterior） directions were （0.21 ± 3.23）,（0.55 ± 3.51） and （0.08 ± 2.76） mm,respectively.The spatial distributions of setup error was maximum in y direction,the second in x direction and the minimum in z direction.The difference of setup errors in x,y,z directions was not statistically significant.MPTV was 5.44 mm in x axis,7.26 mm in y axis,5.68 mm in z axis,repectively.Conclusions The influence of setup errors of a PTV margin would be suggested by 5.5,7.5 and 6 mm on x （left-right）,y （superior-inferior）,z （anterior-posterior）directions for postoperative radiotherapy for endometrial and cervical cancer.