图像引导下鼻咽癌放射治疗中颈部变形旋转误差研究

目的利用不同匹配区域对锥形束CT（CBCT）与定位CT（FBCT）分别配准，测量出鼻咽癌放射治疗中颈部的变形误差。方法分析2007年4月-2008年12月收治鼻咽癌患者23例，调整治疗床前198次CBCT扫描。将鼻咽部扫描CBCT图像匹配区域分为上下两个区域进行对比分析。其中上匹配区域为：上界为蝶窦上缘，下界为颈4下缘，侧界包括下颌骨外轮廓，前界为上颌窦1／2，后界为平棘突后缘；下匹配区域为：上界约颈4下缘，下界约胸2-3下缘，侧界包括椎体外轮廓，前界包括皮肤，后界平棘突后缘。匹配方式选择骨，比较匹配结果差异。结果选择上与下匹配区域结果除Y（头脚）方向旋转误差无统计学差异外，余均有统计学差异（P〈0．05）。差值在X（左右）、Z（前后）、Y（头脚）方向平移分别为（1．14±2．80）、（0．47±1．41）、（0．58±3．88）mm，旋转误差X、Y、Z方向分别为（0．90±1．98）、（0．80±2．03）、（0．68±1．90）°。结论鼻咽癌放射治疗中颈部区域存在一定变形误差，通过CBCT引导发现变形误差并进行正确纠正是必须的，结合临床实际及靶区与危及器官的变化为重新计划提供依据。

Rotation Errors Due to Neck Deformation in Nasopharyngeal Cancer Radiotherapy with Image Guiding

Objective To investigate the rotation errors due to neck deformation in nasopharyngeal cancer （NPC） radiotherapy with different match areas to register conebeam CT（CBCT） from image guiding and fanbeam （FBCT） from simulation. Methods A total of 198 pre-correction CBCT data sets from 23 NPC patients from April 2007 to December 2008 were retrospectively analyzed. The matching areas in CBCT images were divided into up and down region of interest （ROI）. For the up ROI, the superior, inferior, left and right, anterior, and posterior boundary were set parallel with sphenoid sinus up side, C4 down side, mandible outside, and 1/2 of maxillary air sinus and acanthi. For the down ROI, the lines were set parallel with C4 down side, T2-3 down side, neck outside, skin surface and acanthi respectively in all directions. All registrations were performed automatically by bony anatomy and the results were compared. Results The registration results by the up and the down ROI showed significant difference except Y direction for rotation. The translation error was （1.14±2.80）,（0.47±1.41）,and （0.58±3.88） mm, respectively; and the rotation error was （0.90±1.98）,（0.80 ±2.03）,and （0.68±1.90） ° in X, Y, and Z direction, respectively. Conclusions There are some significant deformation errors at neck areas in NPC radiotherapy. It is important to find out the deformation and correct it with CBCT image guiding. This kind of error information may provide clues for re-planning in addition to clinical practice and the changes of clinical targets and involved organs.