Diffusion-weighted MR and apoptosis research in rabbit models of hepatic VX2 tumors after radiotherapy

Abstract

Objective To investigate the imaging characteristic of DWI in rabbit models of hepatic VX2 tumors after three-dimensional stereotactic conformal radiation therapy, and the characteristics of apoptosis after radiotherapy. Methods Sixty hepatic VX2 tumor models were successfully created. 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 time points ( 1 st day, 5 th day, 10 th day, 15 th day) for each group respectively. ROIs of the VX2 tumor tissues and normal liver tissue were taken and ADC values were measured to calculate their ratios. Cell apoptesis were determined by using TUNEL method. ADC values with their ratios and the apoptotic index were analyzed using one-way analysis of variance and SNK test was used for comparison among different time points of groups, while two sample t test was used for comparison between the groups. Results On the 1 st day, 5 th day, 10 th day, and the 15 th day, the ADC ratios of the radiotherapy groups were 0.74 ±0. 15(n =8), 1.04 ±0.09(n =7), 1.43 ±0. 12 (n = 7 ), 1.25 ± 0. 23 (n = 8 ) (F = 24. 221, P ＜ 0. 01 ), the corresponding ADC ratios of control groups were 0. 78 ±0.07(n =5), 0.79 ±0.07(n=4), 0.83 ±0. 14(n =4), 0.97 ±0. 19(n =4). The ratios of ADC values for radiotherapy groups and control group were compared, and the 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 time point. On the 1 st day, 5 th day, 10 th day, 15 th day, the apoptotic index of the radiotherapy groups were 0. 39 ±0. 13(n=8), 0.29 ±0.08(n=7), 0.28 ±0.07(n=7), 0.58 ±0. 19(n=8,F=8. 128,P＜0.05), while the corresponding apoptotic index of control groups were 0. 26 ±0. 13(n =5), 0. 18 ±0. 03(n =4), 0. 16 ±0. 06(n =4), 0. 18 ±0. 08(n =4,F= 1. 006,P ＞0. 05). The apoptotic index value for radiotherapy groups and control group were compared, with t value of 1. 716 ( P ＞ 0.05 ), 2. 348 ( P ＜ 0. 05 ), 2. 386 ( P ＜0. 05 ), 3. 756( P ＜0.01 ) respectively. Conclusion DWI ADC values can reflect the dynamic changes of cell apoptosis in hepatic VX2 tumors after radiotherapy at different time points. Key words: Liver neoplasms,experimental; Diffusion magnetic resonance imaging; Apoptotic