Diffusion-weighted Imaging And Apoptosis Research In Rabbit Models Of Hepatic Vx2 Carcinoma After Radiotherapy

Objective To discuss the imaging characteristic of diffusion-weighted imaging in rabbit models of hepatic VX2 carcinoma after three-dimensional stereotactic conformal radiation therapy,and the characteristics of apoptosis after radiotherapy , and their relevance after radiotherapy.Methods Sixty New Zealand white rabbits received a implantation of VX2 carcinoma cell in their liver to set up tumor model. And two weeks later, after routine scans were performed on 1.5T MR scanner,b value of 500s/mm2 respectively on DWI scaning. After the tumor grew to more than 1 cm in diameter,40 tumor models were treated with SCRT and then divided into four groups using random number table. The remaining 20 tumor models were used as controls and randomly assigned to each group. MR scanning were performed at different times(1st day,5th day,10th day,15th day) for each group respectively. ROIs of the VX2 tumor tissues and normal liver tissue were taken and ADC values measured with calculation of their ratio. Cell apoptosis were determined by using TUNEL method. Calculate the apoptotic index (Apoptotic cells / Tumor cells). ADC value with their ratio and the Apoptotic index were calculated using one dimendional analysis of variance and two samples t-test at different times,compared within the group and between groups by Analysis of Variance. Results On the 1st day,5th day,10th day,15th day,the ADC ratios of the radiotherapygroups were 0.74±0.15,1.04±0.09,1.43±0.12,1.25±0.23,the corresponding ADC ratios of control groups were 0.78±0.07,0.79±0.07,0.83±0.14,0.97±0.19. The ratio of ADC values for radiotherapy groups and control group were compared,t value was 0.569(P > 0.05),4.417(P < 0.05),7.259(P < 0.01),1.957(P > 0.05) respectively for each group. On the 1st day,5th day,10th day,15th day, the apoptotic index of the radiotherapy groups were 0.26±0.13,0.18±0.03,0.16±0.06,0.18±0.08, the corresponding apoptotic index of control groups were 0.26±0.13,0.18±0.03,0.16±0.06,0.18±0.08. The apoptotic index value for radiotherapy groups and control group were compared,with t value was 1.716(P>0.05),2.348(P<0.05),2.386(P<0.05),3.756(P<0.01) respectively. The ADC ratio and apoptotic index correlation analysis showed that they were positive correlation (r=0.453,P<0.05).Conclusion DWI ADC values can reflect the dynamic changes at cell apoptosis for hepatic VX2 tumors after radiotherapy at different times.