摘要：
目的 探讨MRI定位在合并阻塞性肺不张( POLC)肺癌患者中进行靶区勾画的可行性及优势. 方法 对14例合并POLC肺癌患者同时行CT、MRI定位,分别采集CT、T1 WI、 T2 WI、DWI图像并测量癌肿与POLC在T2 WI、DWI图像上的比信噪比( CNRs). 将CT、MRI定位图像在TPS中进行融合,分别在CT、MRI上进行靶区勾画,制定放疗计划. PlanCT、PlanMRI均以CT为基础实现剂量计算,采用相同射野数目及角度. 系统自动计算GTV,比较2个计划的DVH. 配对t检验差异. 结果T2 WI可以显示12/14癌肿与POLC的界限,6/6中肿块与POLC的分界均可被DWI显示. GTVMRI为(149.317±229. 670) cm3,GTVCT为(178.073±236. 604) cm3(P=0. 000). DWI图像CNRs为77.295± 49. 273,T2WI的为12.942±5. 553(P=0. 027). DVH比较显示在靶区适形度及均匀性无差异的前提下,PlanMRI比PlanCT患侧肺平均剂量低( P=0. 002) ,健侧肺平均剂量相近( P=0. 052) ,总肺平均剂量、食管平均剂量、脊髓最大剂量均低(P=0. 009、0. 038、0. 038),患侧肺V5、V10和心脏V25均低(P=0. 010、0. 031、0. 044). 结论 MRI定位用于合并POLC肺癌患者可更精确勾画靶区,减少OARs受量.%Objective To study the potential of MRI simulation in lung cancer patients with post-obstructive lobar collapse ( POLC) . Methods 14 patients with POLC were enrolled. Before radiotherapy, two sets of simulating images were obtained for each patient using CT and MRI with T1/T2-weighted and diffuse-weighted images ( T1 W/T2 WI/DWI) . Simulating MRI were fused with corresponding simulating CT for dose calculation. Contrast-to-noise-ratios ( CNRs) of tumor and POLC on T2 WI and DWI were measured and calculated. The GTV and OARs were delineated separately by radiation oncologists both on simulating CT and MRI. PlanCT and PlanMRI/CT were carried out on CT sets with same beam number and direction. Dose distributions of OARs were compared on the basis of DVH. Results 12 out of 14 cases were distinguishable by T2 WI and all the 6 cases could be figured out by DWI. The mean volume of GTVMRI was significantly smaller than GTVCT(149.317±229. 670 cm3 vs.178.073±236. 604 cm3,P=0. 000).The mean CNR of DWI was much higher than T2WI (77.295±49. 273 vs.12.942±5. 553,P=0. 027).The DVH comparison showed OARs of PlanMRI got less exposure compared to those of PlanCT . with no significant differences in HI and CI ( The mean dose of lung with cancer was lower ( P=0. 002) ,and withno cancer similar ( P=0. 052) . Total lung mean dose was lower ( P=0. 009) ,and with esophagus lower ( P=0. 038) . The maximal dose of spinal cord was lower ( P=0. 038) . The V5 ,V10 of lung and V25 of heart were lower ( P=0. 010,0. 031,0. 044) . Conclusions MRI simulation with coregistered simulating CT is more competent than CT simulation alone, in identifying and defining the borderlines of tumor masses and reducing the exposure of OARs.
