大孔径MRI模拟定位机引导鼻咽癌靶区勾画的初步研究

Role of large-diameter MRI simulation in target volume delineation in radiotherapy for nasopharyngeal carcinoma

目的探讨大孔径MRI模拟定位机在鼻咽癌靶区勾画方面的应用。方法18例可进行CT及MRI扫描的鼻咽癌患者，分别利用SOMATOM Sensation Open40排82CITI大孔径CT模拟定位机；西门子3T磁共振系统MAGNETOM Skyra 70cm大孔径模拟定位机在同一体位下进行CT及MRI扫描定位。按照ICRU50、62号文件分别进行GTV及腮腺勾画，利用MRI观察GTV及腮腺在放疗过程中体积变化。采用配对t检验分析GTVCT与GTVMRI GTVnx-CT与GTVnx-MRI差异，GTVnd-CT与GTVnd-MRI差异分析采用Wilcoxon检验。结果GTVMRI较GTVCT体积明显缩小，平均体积由（213．64±84．59）cm。缩小至（199．68±84．69）cm3（P=0．006）。鼻咽原发灶GTVnx-MRI较GTVnx-CT缩小，体积由（95．75±24．76）cm。缩小至（88．12±26．25）cm3（P=0．001）。颈部淋巴结GTVnd-MRI较GTVnd-CT缩小，体积由（117．89±72．69）cm3缩小至（111．56±70．69）cm3（P=0．018）。且CT及MRI靶区勾画不完全重合，差异主要体现在颅底骨质及颈部软组织方面。MRI引导勾画左右腮腺体积较CT引导勾画左右腮腺体积增大，差异主要体现在腮腺深叶勾画。MRI显示GTV在整个放疗过程中体积缩小约（82．64±16．87）％。左、右腮腺体积分别缩小约（32．7±23．95）％、（34．7±21．72）％。结论MRI模拟引导勾画靶区较CT模拟勾画靶区更精确，体积范围缩小，有助于进一步精确指导鼻咽癌靶区勾画。

Objective To investigate the role of large-diameter magnetic resonance imaging （MRI） simulation in target volume delineation in radiotherapy for nasopharyngeal carcinoma （ NPC ） . Methods Eighteen patients with NPC underwent computed tomography （CT） simulation and MRI simulation scans and localization in the same body position, with SOMATOM Sensation Open 40-row 82-cm large-diameter CT simulator and Siemens 3T MRI MAGNETOM Skyra 70-cm large-diameter simulator, respectively. The gross tumor volume （GTV） and parotid glands were delineated on all images according to the ICRU Report 50/62, and MRI was applied to observe the changes in GTV and parotid volume during radiotherapy. Paired t-test was applied to analyze the differences between GTVcT and GTVMRI and between GTVnx-CT and GTVnx-MRI. Results GTVMal decreased significantly compared with GTVCT, and the average volume decreased from （213.64±84. 59）cm3 to （ 199.68± 84. 69）cm3（ P=0. 006）. As for the volume of primary lesions in the nasopharynx, GTVnx_Mm was significantly smaller than GTVnx-CT, and the volume decreased from （95.75±24. 76） cm3 to （ 88.12±26. 25） cm3（ P = 0. 001 ） ;as for the volume of cervical lymph nodes, GTVnd-Mm was significantly smaller than GTVnd-CT, and the volume decreased from （117.89± 72. 69） cm3 to （111.56±70. 69 ） cm3 （ P= 0. 018 ） . The targets delineated by CT and MRI did not overlap completely , with major differences in skull base bone and cervical soft tissue. The volume of both parotid glands delineated on MRI image was higher than that dehneated on CT image, with a major difference in the deep lobe. MRI showed that GTV was reduced by 82.64±16. 87% during radiotherapy, and the volumes of the left and right parotid glands were reduced by （ 32.7±23.95 ） % and （ 34.7±21.72 ） %, respectively. Conclusions The delineation of target volume based on MRI simulation is more accurate than that based on CT simulation and can achieve a smaller volume range, which helps to guide target volume delineation in radiotherapy for NPC accurately.