CT—MRI图像融合在脑胶质瘤术后精确放疗中的应用分析

Observation of CT-MRI image fusion in postoperativeprecise radiotherapy for gliomas

目的探讨CT-MRI图像融合在脑胶质瘤术后精确放疗靶区勾画中的应用价值。方法收集首诊为脑胶质瘤的36例患者行术后IMRT，采用标点法（L）＋手动融合法（M）＋互信息法（MI）进行图像融合，并分别根据CT图像及融合图像勾画靶区及OAR，成组t检验体积差异。计算CT及MRI图像上相应标记点的距离误差，并采用体积法及几何中心法计算其体积交叠度及中心位置距离。结果采用L＋M＋MI法进行图像融合有着较高融合精度，融合误差均〈2mm。Ⅲ—Ⅳ级胶质瘤组GTVCT比GTVMRI减少，分别为（74．62±46．91）、（105．99±58．86）cm^3（P=0．042）；CTVCT比CTVMRI也减少，分别为（304．03±130．05）、（387．94±150．12）cm^3（P=0．040）。融合前后视交叉中心位置变化最小（1．32±1．42）mm，CTV中心位置变化最大（7．99＋11．06）mm，其次为GTV、脑干。结论CT-MRI图像融合有助于减少靶区勾画的不确定性，特别是对有水肿区存在及术后病灶残存患者价值更大。

Objective To investigate the value of computed tomography （CT）-magnetic resonance imaging （MRI） image fusion in target volume delineation of postoperative precise radiotherapy for gliomas. Methods Thirty-six patients newly diagnosed with gliomas were enrolled and received postoperative intensity-modulated radiotherapy. Landmark （ L ） combined with manual fusion （ M ） and maximization of mutual information （MI） was used for image fusion. Target volume and organs at risk were delineated based on CT images and fused images, respectively. Comparison of the volume was made by pairwise t test. The distance from a landmark on CT image to the corresponding one on MRI image was calculated. The volume method and geometric center method were used to calculate the degree of volume overlap and changes in central positions after image fusion. Results The L＋M＋MI method achieved a high registration accuracy in image fusion, with a registration error less than 2 mm. In patients with grade Ⅲ-Ⅳ gliomas, the CT images yielded significantly smaller gross tumor volume （ GTV ） and clinical target volume （ CTV ） than the MRI images （74.62±46. 91 vs. 105.99±58.86 cm^3 , P= 0. 042; 304.03±130. 05 vs. 387.94±150. 12 cm^3, P= 0. 040）. After image fusion, the smallest change in central position occurred in the chiasma （1.32±1.42 mm） , and the largest change occurred in CTV （7.99±11.06 ram） , followed by GTV and the brain stem. Conclusions CT-MRI image fusion helps to reduce the uncertainty of target volume delineation in patients with gliomas, especially in those with edema and residual tumor after surgery.