鼻咽癌调强放疗摆位误差大小和变化趋势监测

Monitoring of Setup Error Measurement and Variationtrend During IMRT for Nasopharyngeal Carcinoma

[目的]分析采用个体化加长真空垫+热塑网状头颈肩膜体位固定技术实施调强放疗的鼻咽癌患者放疗期间摆位误差的大小及其体重的变化趋势。[方法]鼻咽癌患者23例,整个疗程1～6个周次中每周拍摄正侧位EPID图像一次并测量患者体重。将EPID图像与计划CT所生成的DRR图像进行配准,利用获得的配准差值分析摆位误差的大小及其在不同周次间的差异,同时分析患者体重的变化对摆位误差的影响。[结果]不分周次的情况下,头脚、腹背、左右三个方向的摆位误差分别为0.165±0.121cm、0.064±0.122cm、0.038±0.135cm。按不同周次进行划分,头脚、腹背、左右各个方向在6个不同周次的摆位误差无明显差别(P均>0.05)。Bivariate相关分析结果显示头脚、腹背、左右三个方向上的偏移幅度与体重变化均无关(r=0.147,P=0.152;r=0.102,P=0.321;r=0.114,P=0.267)。[结论 ]采用个体化加长真空垫+热塑网状头颈肩膜体位固定技术实施调强放疗的鼻咽癌患者在整个疗程中的摆位具有较好的准确性与重复性,患者体重的变化对摆位误差无明显影响。

[Purpose] To analyze the setup errors and the body weight trends of the nasopharyn- geal carcinoma （NPC） patients during intensity modulated radiation therapy （IMRT） using the thermoplastic masks and individualized lengthen vacuum pads. [Methods] Twenty-three cases with NPC were treated with IMRT and carried out the electric portal image device （EPID） and body weighted once a week during the 6-week course of treatment. Previously,treatment machine calibration was also performed to ensure the accuracy of EPID system. Registration based on the EPID images and the Digitally Reconstructed Radiograph （DRR） images which were formed from CT scan in the treatment planning system,the values of group set-up errors and weekly differences was analyzed. Meanwhile,the effect of changes in body weight on, setup errors was analyzed. [Results] Regardless of weekly differences,the setup errors in the lateral （RL）,anteroposterior （AP） and superior-inferior （SI） directions was 0.165＋0.121,0.064＋0.122 and 0.038＋0.135cm re- spectively. According to different week,the 6-weekly set-up errors in RL,AP,SI directions had no obviously significant differences （P〉0.05）. Bivariate correlation analysis showed that the migration in three direction had no significant correlation with changes of body weight （r=0.147 ,P=0.152; r= 0.102, P=0.321; r=-0.114, P=0.267）. [ Conclusion ] There is good repeatability and accuracy in IM- RT for NPC patients with individualized lengthens vacuum pads and thermoplastic masks. The chan^e of body weight is no effect on set-up errors.