Objective To investigate the application value of vacuum pad with thermoplastic film in the immobilization of kyphosis patients using Elekta cone beam CT (CBCT).Methods Admitted from May 2013 to February 2017,70 kyphosis patients were selected and divided into head-neck group,thorax group and abdomen group.The CBCT scan was performed weeny to obtain X-ray images which were compared with planning CT images generated from treatment planning system to analyze the set-up errors.Patients in the same group were randomly treated by combined fixed mode (vacuum pad combined with thermoplastic phantom) and single fixed mode (thermoplastic phantom only).The set-up errors of different fixed modes were tested by paired t-test.Results In head-neck group,the linear set-up errors at x (left-right),y (anterior-posterior) and z (head-foot) directions were (0.82±0.74),(1.58±1.03) mm;(0.76±0.57),(1.37±0.88) mm;(0.85±0.55),(1.82±0.79) mm for combined fixed mode and single fixed mode,respectively (P=0.005,0.006,0.006),and the rotational set-up errors were 0.75°±0.63°,1.08°±0.92°;0.68°±0.57°,1.26°±0.78°;0.75°±0.82°,0.98°±0.89°,respectively (P=0.016,0.023,0.036).In thorax group,the linear set-up errors at x,y and z directions were (1.63±0.87),(2.67±0.68) mm;(1.62±0.62),(2.86±0.81) mm;(1.79±0.89),(3.27±0.68) mm for combined fixed mode and single fixed mode,respectively (P=0.008,0.007,0.004),and the rotational set-up errors were 0.88°±0.72°,1.26°±0.83°,0.92°±0.55°,1.33°±0.92°,0.71°±0.62° 、0.97°±0.69°,respectively (P=0.025,0.036,0.042).In abdomen group,the linear set-up errors at x,y and z directions were (1.34±0.69),(2.01±0.96) mm;(1.27±0.87),(1.89±0.71) mm;(1.38±0.77),(2.25±0.82) mm for combined fixed mode and single fixed mode,respectively (P=0.033,0.027,0.016),and the rotational set-up errors were 0.75°± 0.87°,1.12°±0.62°;0.88°±0.75°,1.08°±0.71°;0.74°±0.62°,0.92°±0.59°,respectively (P=0.026,0.038,0.154).The linear errors at 3 directions of combined fixed mode were smaller than those of single fixed mode (P＜0.05).For the patients in head-neck and thorax groups,the rotational set-up errors of combined fixed mode were smaller at all 3 directions,but the rotational set-up errors of combined fixed mode in abdomen group were smaller than those of the single fixed mode only in x and y directions (P＜0.05).Conclusion The fixed mode of vacuum pad combined with thermoplastic phantom provides a guarantee for the positioning repeatability of kyphosis patients,providing more benefits to patients with head-neck and thorax tumors compared with patients with abdomen tumor.%目的:利用医科达机载锥形束CT(CBCT)研究真空垫配合热塑膜固定在脊柱后凸患者放疗中的应用价值.方法:选择2013年5月～2017年2月入院的70例脊柱后凸患者,分为头颈部组、胸部组、腹部组,每周行CBCT扫描,将采集的X线容积图像与计划CT图像比较分析摆位误差.组内随机分为组合固定模式和热塑膜单一固定模式,摆位误差在不同组内进行配对t检验.结果:头颈部组合固定模式组和单一固定模式纽患者左右x、前后y、上下z方向的线性摆位误差分别为:(0.82±0.74)、(1.58±1.03)mm;(0.76±0.57)、(1.37±±0.88)m m;(0.85±0.55)、(1.82±0.79)mm(P=0.005、0.006、0.006);旋转摆位误差分别为:0.75°±0.63°、1.08°±0.92°;0.68°±0.57°、1.26°±0.78°;0.75°±0.82°、0.98°±0.89°(P=0.016、0.023、0.036).胸部组合固定模式组和单一固定模式组患者左右x、前后y、上下z方向的线性摆位误差分别为:(1.63±0.87)、(2.67±0.68)mm;(1.62±0.62)、(2.86±0.81)mm;(1.79±0.89)、(3.27土0.68)mm(P=0.008、0.007、0.004);旋转摆位误差分别为:0.88°±0.72°、1.26°±0.83°;0.92°±0.55°、1.33°±0.92°;0.71°±0.62°、0.97°±0.69°(P=0.025、0.036、0.042).腹部组合固定模式组和单一固定模式组患者左右x、前后y、上下z方向的线性摆位误差分别为:(1.34±0.69)、(2.01±0.96) mm;(1.27±0.87)、(1.89土0.71)mm;(1.38±0.77)、(2.25±0.82) mm(P=0.033、0.027、0.016);旋转摆位误差分别为:0.75°±0.87°、1.12°±0.62°;0.88°±0.75°、1.08°±0.71°;0.74°±0.62°、0.92°±0.59°(P=0.026、0.038、0.154).组合固定模式线性误差在3个方向均小于单一固定模式组(P＜0.05);头颈部及胸部患者旋转方向摆位误差,组合固定模式在3个方向均好于单一固定模式组;但腹部患者组合固定模式仅在前后及上下方向优于单一固定模式组(P＜0.05).结论:真空垫配合热塑膜的固定技术为脊柱后凸患者的体位重复性提供保障,头颈部和胸部患者受益大于腹部患者.
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