机载影像系统在盆腔肿瘤精确放疗摆位中的临床研究

 目的　应用Varian ix加速器机载影像（OBI）系统研究盆腔肿瘤精确放疗摆位误差，为临床提供参考数据。方法 对适形调强放疗的15例盆腔肿瘤患者进行研究，测量患者左右（X）、头脚（Y）、前后（Z）3个方向的线性误差以及分别以X、Y、Z轴旋转形成的相应U、V、W旋转误差，在线校正摆位误差并记录误差值。统计校正前后的误差，采用二参数法计算临床靶体积（CTV）到计划靶体积（PTV）的外放边界（MPTV）。结果 15例患者共行146次首次摆位后和治疗后锥形束CT扫描，在X、Y、Z方向上系统误差（均数）±随机误差（标准差）分别为（1.23±0.134）、（-2.02±7.96）、（-1.87±3.13）mm，治疗后分别为（0.49±1.14）、（-0.98±2.28）、（-1.87±3.13）mm。X方向的锥形束CT扫描摆位床值在首次摆位后及校正前、后的差异无统计学意义，在Y和Z方向的差异均有统计学意义，校正后的摆位误差在Y和Z方向低于首次摆位后（P＜0.05）；U、V、W 3个方向上摆位误差分别为（0.72±1.23）°、（0.06±1.12） °、（0.12±0.97）°，旋转误差一般不超过3°。由于在线校正只对平移误差进行了校正，U、V、W校正前后无差异。纠正前X、Y、Z方向的MPTV分别为2.55、9.61、5.93 mm，纠正后分别为1.78、3.55、2.74 mm。结论 使用OBI系统在线或离线指导摆位误差的修正可以提高摆位的精度，减少摆位的不确定性，在维持或提高局控率的同时，减少周围正常组织的照射，从而达到提高治疗精度的目的。

OBI clinical studies of setup errors in precise radiotherapy of pelvic carcinoma

Objective To study setup errors in precise radiotherapy by Varian ix accelerator OBI system and provide reference data for clinic. Methods 15 patients with pelvic cancer patients were studied in intensity modulated radiation therapy, measurement in patients with left and fight （X）, head and feet （Y）, before and after the （Z） 3 directions respectivelY, the linear error and X, Y, Z axis to form the corresponding U, V, W rotation errors, online error correction anyway, and record the error values. The error data was analyzed before and after corrections using the two-parameter method to calculate the clinical target volume （CTV） to planning target volume （PTV） of putting boundaries （MPTV）. Results 15 patients were preformed total 146 times of the first place after a and after treatment of conical CT scan, in the X, Y, Z direction system error （x） ± random error （s） were （1.23±0.134） ram, （2.02±7.96） mm and （1.87±3.13） ram, after treatment for respectively （0.49±1.14） mm, （0.98±2.28） mm and （1.87±3.13） mm. There was no significant difference on X direction of the tapered bed CT scan in the firgt place, before and after calibration, in Y and Z direction there were significant differences, corrected position error in Y and Z direction is lower compared with that of primary （P 〈 0.05）; the setup error were （0.72±1.23）°, （0.06±1.12）°, （0.12±0.97）° on U, V and W direction respectively, rotate error in general was not more than 3°. Since online correction only worked to the translation error correetion, There was no differenee in U,V and W before and after eorrection.The MPTV was 2.55, 9.61 and 5.93 mm on X, Y, Z direction before correcting. Conclusions Online or offline using the OBI system to guide positioning error correction can improve the positioning accuracy and reduce the positioning uncertainty, while maintaining or inereasing local control rate at the same time, reducing exposure to surrounding normal tissue, so as to improve treatment aeeuraey purposes.