利用兆伏级CT分析头颈部肿瘤在螺旋断层放疗中的摆位误差

目的：应用螺旋断层放疗机（Tomo therapy）自带的兆伏级CT（MVCT）影像引导，测定并分析采取面网固定方式的头颈部肿瘤患者的摆位误差，并依此计算CTV-PTV外扩Margin值的大小。方法对34例采取面网固定装置的头颈部肿瘤患者，每次治疗前均行MVCT扫描，将扫描所得MVCT图像与定位图像（kVCT）行靶区位置配准，分析患者左右（x）、头脚（y）、腹背（z）和横断面旋转（Roll）方向的误差值，根据公式M＝2．5∑＋0．7σ计算出合理的CTV-PTV外扩Margin值。结果34例患者共行640次MVCT扫描，线性误差在x、y、z方向的系统误差＆#177;随机误差分别为：（-0．15＆#177;0．55） mm、（0．30＆#177;0．56） mm、（0．35＆#177;0．71）mm；在Roll方向的旋转误差为（-0．07＆#177;0．52）＆#176;。 CTV-PTV外放边界在x、y、z三个方向Margin值分别为3．31 mm、5．32 mm和3．35 mm。结论通过对摆位误差的分析为CTV-PTV外扩边界提供了理论依据，为精确放疗提供必要的质量保证。

Analysis of setup errors in the head and neck tumor by Tomo therapy using MVCT scanning

Objective To investigate the setup errors of head and neck tumor patients with head mask-ing by TomoTherapy with megavoltage CT （MVCT）,and to measure the CTV -PTV margins.Methods There were 34 patients with head and neck tumor .All patients had received MVCT scanning before radiation was deliv-ered.The MVCT images were registered with the kilovoltage CT （kVCT）images,the setup errors of the left -right （x）,anterior-posterior（y）,superior-inferior（z）and transverse profile rotation（Roll）were obtained by matc-hing MVCT with kVCT,followed by calculating the reasonable CTV -PTV margins with the formula M=2.5∑＋0.7σ.Results Six hundred and forty MVCT images in total were received for the patients ,the systemic ＆#177;random errors in x,y,z and Roll directions were （ -0.15 ＆#177;0.55） mm,（0.30 ＆#177;0.56） mm,（0.35 ＆#177;0.71） mm and （-0.07 ＆#177;0.52）＆#176;,the CTV-PTV margin in x,y and z directions were 3.31 mm,5.32 mm and 3.35 mm.Con-clusion we demonstrate a theoretic foundation for our CTV -PTV margins in head and neck tumor patients by analyzing the setup errors ,and it also can provide necessary quality assurance for precise radiation .