脑转移瘤大分割立体定向放射治疗中体位固定设备联合摆位引导方式的优选研究

Optimization of immobilization and positioning methods in hypofractionated stereotactic radiotherapy for brain metastases

目的比较开放式面罩联合光学表面监测系统(OSMS)引导摆位与闭合式面罩联合激光灯+面罩标记引导摆位之间的平移和旋转方向误差,评估开放式面罩联合OSMS引导摆位方式在脑转移瘤大分割立体定向放射治疗(HSRT)的应用优势,并计算脑转移瘤患者在不同固定设备与摆位方式下计划靶区体积(PTV)的外放边界。方法回顾性分析55例脑转移瘤患者HSRT的摆位数据,根据固定设备和摆位引导方式的不同,分为OSMS联合开放式面罩组(A组)、头颈肩封闭式面罩+发泡胶组(B1组)和头颈肩封闭式面罩+头枕组(B2组)。A组利用OSMS自动移床功能引导摆位,B1组和B2组利用激光灯+面罩标记引导摆位。3组均通过锥形束CT(CBCT)骨性配准得到六维方向(x轴、y轴、z轴、x轴旋转、y轴旋转、z轴旋转)摆位误差,并根据van Herk公式计算计划靶区的外放边界。结果共采集CBCT配准数据288套,其中A组六维方向摆位误差和3D矢量误差均最小,分别为(0.47±0.33)、(0.49±0.31)、(0.44±0.31)mm,(0.42±0.32)°、(0.48±0.31)°、(0.42±0.22)°和(0.90±0.39)mm;除z轴旋转方向A组与B1组差异无统计学意义外(P>0.05),其余方向与B1组和B2组比较,差异均有统计学意义(P<0.05);且A组无平移方向≥2 mm,旋转方向≥2°的摆位误差。B1组y轴、z轴、z轴旋转方向及3D矢量误差均显著小于B2组,且差异有统计学意义(P<0.05)。A组3个方向PTV外放边界分别为1.32、1.19和1.22 mm,均小于另外两组。结论脑转移瘤HSRT中,与头颈肩封闭式面罩联合激光灯+面罩标记引导摆位相比,应用开放式面罩联合OSMS引导摆位,可明显提高六维方向摆位精度,降低重复摆位率,减小PTV外放边界,具有临床应用价值。

Objective To compare translational and rotational setup errors between immobilization with open masks combined with positioning with the optical surface monitoring system(OSMS)and immobilization with full masks combined with positioning with laser lights and mask markers,find the advantages of open masks combined with OSMS in hypofractionated stereotactic radiotherapy(HSRT)for brain metastases,and calculate planning target volume(PTV)expansions with different immobilization and positioning method for patients with brain metastases.Methods The setup data of 55 patients with brain metastases who received HSRT were analyzed retrospectively.According to immobilization and positioning method,the patients were divided into group A(OSMS+open masks),group B1(full head-neck-shoulders masks+polyurethane foam cushions),and group B2(full head-neck-shoulders masks+standard headrests).Positioning was directed by automatic couch motion in OSMS in group A and by laser lights and mask markers in groups B1 and B2.Cone beam computed tomography(CBCT)scans were registered using the bone registration method to obtain setup errors in six directions(x,y,z,roll,pitch,yaw).PTV expansions were calculated according to the van Herk formula.Results A total of 288 sets of CBCT registration data were acquired.Among three groups,group A showed the smallest mean setup errors and 3D vector error,which were(0.47±0.33)mm,(0.49±0.31)mm,(0.44±0.31)mm,(0.42±0.32)°,(0.48±0.31)°,(0.42±0.22)°,and(0.90±0.39)mm,respectively.Group A differed significantly from group B1 and group B2 in the errors at all directions(P<0.05)except for the yaw direction compared with group B1(P>0.05).Group A had no setup error≥2 mm in translational directions or≥2°in rotational directions.Group B1 showed significantly smaller setup errors in the y,z,and yaw directions and 3D vector error than group B2(P<0.05).In group A,PTV expansions in three directions(x,y,and z)were 1.32,1.19,and 1.22 mm,respectively,which were smaller than those of the other two groups.Conclusions In HSRT for patient with brain metastases,compared with full head-neck-shoulders masks combined with laser lights and mask markers,open masks combined with OSMS can significantly improve setup precision in six directions and reduce repeated setup and PTV expansions,which shows promise for clinical application.