射波刀六维颅骨追踪方式治疗脑转移瘤的体位误差分析

目的采用射波刀六维颅骨(6D-skull)追踪方式治疗脑转移瘤,对治疗过程中体位误差进行分析,为临床放射治疗靶区的勾画提供参考。方法选取2021年9月至12月在本院接受第六代射波刀治疗的50例立体定向放射治疗(SRT)脑转移瘤患者,中位年龄60岁。治疗过程中间隔90 s采集一组正交图像,与数字重建图像(DRR)进行自动配准并记录误差值。分析治疗前期、治疗中期及治疗后期三个时间段的体位误差,根据公式MPTV=2.5Σ+0.7δ计算肿瘤靶区(GTV)到计划靶区(PTV)的外扩边界范围。结果50例患者在治疗过程中采集到6个方向共3,144组数据,三个线性方向体位误差(x±s)分别为:X(0.32±0.29)mm,Y(0.31±0.25)mm,Z(0.23±0.19)mm;三个旋转方向体位误差(x±s)分别为:Roll(0.26±0.23)°,Pitch(0.33±0.26)°,Yaw(0.65±0.55)°。三个线性方向X、Y、Z的外放边界分别为1.00 mm、0.95 mm、0.71 mm。除Yaw方向外,其余5个方向在治疗前和治疗期间的误差值差异均有统计学意义(P<0.05),并且6个方向的体位误差在治疗期间随着治疗时间有所增大。6个方向之间相关性分析显示X-Y、Y-Z及Z-Yaw不具有相关性(P>0.05),其他组别两两相关性均具有统计学意义(P<0.05),其中X-Pitch和Y-Roll具有较强正相关性,其余存在较弱正相关性。结论6D-skull追踪方式治疗脑转移瘤时可以很好监测并修正治疗过程中的体位误差,达到精准放疗的要求。

Objective To analyze the postural errors in the treatment of brain metastases by using Cyberknife 6D-skull tracing method,so as to provide reference for clinical delineation of target sites.Methods Fifty patients with brain metastases were selected,with a median age of 60 years.A set of orthogonal images were collected at 90s interval,which were automatically registered with digital reconstruction image(DRR)and the error value was recorded.The position errors before treatment,during treatment and three time periods during treatment were analyzed.The extended boundary range from Gross Tumor Volume(GTV)to Planning Target Volume(PTV)was calculated by the formula M=2.5Σ+0.7δ.Results A total of 3144 sets of data in 6 directions were collected from 50 patients during treatment.The three linear directions of body position error(x±s)were:X(0.32±0.29)mm,Y(0.31±0.25)mm,Z(0.23±0.19)mm.The three rotation direction body position errors(x±s)were:Roll(0.26±0.23)°,Pitch(0.33±0.26)°,Yaw(0.65±0.55)°.The outward bounds of the three linear directions X,Y,and Z were 1.00 mm,0.95 mm,and 0.71 mm respectively.Except for the Yaw direction,the error values of the other 5 directions were significantly different before and during the treatment(P<0.05)The body position error of the 6 directions increased with the treatment time during the treatment.The correlation analysis between the 6 directions showed that X-Y,Y-Z and Z-Yaw had no correlation(P>0.05),and the other groups had statistically significant correlations(P<0.05).The X-Pitch and Y-Roll had a strong positive correlation,and the rest had a weak positive correlation.Conclusion The 6D-skull tracking method of Cyberknife in the treatment of brain metastases can well monitor and correct the body position error during the treatment,so as to meet the requirements of precise radiotherapy.