锥形束CT引导下盆腔肿瘤患者在六维床上不同固定体位的摆位误差及靶区外放边界

Positioning errors and margin of planning target volume of pelvic tumors patients in different fixed positions on a six-dimensional bed guided by cone beam CT

目的探讨锥形束CT(CBCT)引导下盆腔肿瘤患者在六维床上不同固定体位的摆位误差以及靶区外放边界(M_(PTV))。方法将60例盆腔肿瘤患者按照固定体位的不同分为试验组(n=30)和对照组(n=30),试验组患者采用仰卧位,利用真空负压带与固定板进行固定,对照组患者采用侧卧位,利用腹部固定装置配合摆位支撑器固定。两组患者均进行CBCT扫描,获取CBCT图像后进行配准,获取6个方向的摆位误差,分别为左右(X)、头脚(Y)、前后(Z)、平移与旋转冠状位(Rx)、矢状位(Ry)、横断位(Rz)。根据M_(PTV)外放边界公式M_(PTV)=2.5∑+0.7σ,计算出平移方向(X、Y、Z)的M_(PTV)值。结果试验组患者X、Y方向的摆位误差均明显大于对照组,差异均有统计学意义(P﹤0.01)。试验组患者Z、Rx、Ry、Rz方向的摆位误差均小于对照组,差异均有统计学意义(P﹤0.05)。试验组患者在Y方向上获取的M_(PTV)值最小,对照组患者在Z方向上获取的M_(PTV)最小。结论CBCT引导下盆腔肿瘤患者在六维床上的仰卧位配合固定装置与侧卧位配合固定装置均存在摆位误差。临床选择患者的固定体位时需要结合患者自身情况以及患病程度、心理、患病位置等多种要素综合考虑摆位误差的影响。

Objective To investigate the positioning errors and margin of planning target volume(M_(PTV))of pelvic tu-mors patients in different fixed positions on a six-dimensional bed guided by cone beam CT(CBCT).Method A total of 60 patients with pelvic tumors were divided into experimental group(n=30)and control group(n=30)according to different fixed positions.The experimental group was supine and fixed with vacuum negative pressure belt and fixation plate,while the control group was lateral and fixed with abdominal fixation device and positioning support.CBCT scans were performed in the two groups to obtain CBCT images and then registration was performed to obtain positioning errors in 6 directions,including left and right(X),head and foot(Y),front and back(Z),translation and rotation coronal position(Rx),sagittal position(Ry),and transverse position(Rz).The M_(PTV) values for the translation direction(X,Y,Z)were calculated according to M_(PTV) external boundary formula M_(PTV)=2.5∑+0.7σ.Result The positioning errors in X and Y direc-tions of experimental group were significantly greater than those in control group,and the differences were statistically significant(P<0.01).The positioning errors in Z,Rx,Ry and Rz directions of experimental group were smaller than those in control group,and the differences were statistically significant(P<0.05).The M_(PTV) values obtained by the experimental group were the smallest in the Y direction,and the M_(PTV) values obtained by the control group were the smallest in the Z direction.Conclusion There are positioning errors in supine position with fixation device and lateral position with fixation device for pelvic tumors patients guided by CBCT on the six-dimensional bed.The selection of a patients’fixed position in clinical practice requires comprehensive analysis of patients’own conditions,degree of disease,psychology,location of disease and other factors to consider the impact of positioning errors.