MR弥散加权成像评估兔肝VX2肿瘤放疗后再增殖

目的 探讨磁共振弥散加权成像评估兔肝VX2肿瘤放疗后肿瘤细胞再增殖的可行性。方法 以经腹腔瘤块种植法建立32只兔肝VX2肿瘤模型,瘤体直径≥1 cm时行单次三维立体适形放疗,放疗剂量15 Gy。将兔平均分为4组,于术后第1、5、10、15天进行MR检查,取b值300、500、600 s/mm²分别进行DWI,测量VX2肿瘤、肝脏ROI的ADC值,计算两者比值,并与病理结果对照。结果 DWI图上VX2肿瘤信号高于肝实质。放疗后VX2肿瘤T2WI信号不均,DWI图上肿瘤实性部分信号不均匀减低,坏死液化部分呈明显低信号,ADC图则相反;放疗后不同b值下不同时间组ADC均值及比值均有显著差异,不同时间组的ADC均值及比值两两比较差异均有统计学意义,肿瘤ADC值及比值放疗后第5天组高于第1天组,第10天组低于第5天组,第15天组低于第10天组。VX2肿瘤ADC值及比值的变化与病理所示肿瘤细胞变化相符。结论 DWI能反映肿瘤组织内微观改变,可用于监测兔肝VX2肿瘤放疗后不同时间点肿瘤细胞的再增殖变化。

MR diffusion weighted imaging in evaluation on cancer cell repopulation for rabbit models of hepatic VX2 tumor after radiotherapy

Objective To observe the feasibility of DWI in evaluating cancer cell repopulation for rabbit models of hepatic VX2 tumor after radiotherapy. Methods VX2 liver cancer models were established in 32 rabbits using celiac tumor block planting method. Three-dimensional stereotactic conformal radiation therapy was performed in each rabbit when the diameter of tumor is equal or greater than 1 cm (single radiation, dose 15 Gy). After radiotherapy, 32 rabbits were randomly averagely divided into four groups, and MRI was performed on 1st, 5th, 10th, 15th day, respectively with EPI-SE sequence and SENSE technology. DWI was performed with different b values (300, 500 and 600 s/mm²). ROIs of VX2 tumor and normal liver tissue were selected, the ADC values of ROI as well as ADC_tumor/ADC_liver ratios were calculated, statistically analyzed and compared with pathology findings. Results Signal intensity of VX2 tumor on DWI was higher than that of liver tissue. After radiotherapy, signal intensity of VX2 tumor became heterogeneous on T2WI. The signal of solid part decreased unevenly, while the necrotic cystic part showed very low signal on DWI, while ADC images behaved in the opposite way. Significant differences were found in ADC value and ADC_tumor/ADC_liver among different time groups with different b value. There were significant differences in ADC value and ADC_tumor/ADC_liver between every two groups. ADC_tumor value and ADC_tumor/ADC_liver on the 5th day after operation were higher than that on 1st day, on the 10th day after operation were lower than that on the 5th day, on the 15th day after operation were lower than those on the 10th day. Changes of ADC values and ADC_tumor/ADC_liver accorded with cellular changes in pathological samples. Conclusion Micro changes of tumor tissue can be reflected with DWI images through changes of ADC_tumor images, ADC_tumor values and ADC_tumor/ADC_liver. DWI can be used to monitor cancer cell repopulation of rabbit VX2 liver cancer at different time after radiotherapy.