| Objective: Esophageal cancer is a common malignant tumor in China, and radiotherapy is one of the main treatment methods of it. The effect of radiotherapy for esophageal cancer is closely related to radiation sensitivity in each individual. But until now, there is no effective method which can predict and evaluate the radiation sensitivity at the early stage after radiotherapy. This study adopts animal model to examine the prediction and evaluation value of diffusion-weighted magnetic resonance imaging(MR-DWI) on radiation sensitivity, which can provides valuable theoretical basis for the reasonable application of this imaging technique in clinic.Methods:1 BALB/c nude mice were subcutaneously injected with Eca-109 cell lines. After tumor formation, 24 nude mice bearing regular-shaped xenograft for experimental use were picked. 24 nude mice were randomly divided into experimental group(n=14) and control group(n=10), and the experimental group received a single dose of 15Gy(6MV X-rays) delivered by a medical linear accelerator.2 Tumor bearing mice were scanned with a 3.0T MRI system(SIEMENS) before and after radiotherapy at different time points(1, 6, 13 days) under an anesthesia state. The check sequence included T1 WI, T2 WI, and DWI. ADC values were measured before radiotherapy(ADC0) and the checked time points after radiotherapy(ADCX, X=1, 6, 13). The ADC value's change rate was defined as ?ADC and calculated by the following formula: ?ADC=(ADCX-ADC0)/ADC0×100%.3 Long and short diameters of each xenograft were measured by one researcher every other day after radiotherapy. The xenograft volume's change rate at different check points was indicated by(VX-V0)/V0×100%.4 Statistical analysis was performed with SPSS21.0 software packages.Results:1 Comparison of ADC values and the ADC values' change rate between the experimental group and the control groupIn the experimental group, the ADC values were decreased at the first day, increased at the sixth day and the thirteenth day gradually. However, the ADC values of the control group showed a gradual decrease. Repeated measures analysis of variance results suggested that the differences of ADC values between the checked time points after radiotherapy and before radiotherapy were significant. Multivariate analysis of variance results showed that there was no significant difference in ADC0 values between the two different groups before radiotherapy(P=0.991, <0.01), while significant difference was found in the ADC values(ADCX, X=1, 6, 13) after radiotherapy(P=0.021, 0.001, 0.000, <0.05). The change rate of ADC values in different time points were also significantly different between the two groups(P=0.006?0.002?0.000, <0.05).2 Xenograft volume changes analysis between the experimental group and the control groupThe xenograft volume in the experimental group showed a significant growth delay when compared with the control group. The growth doubling time was 24 days in the experimental group and 5 days in the control group. There was no significant difference in xenograft volume between the two groups(P=0.393,>0.05) before radiation. Multivariate analysis of variance results further suggested that significant difference in xenograft volume between the two groups only began to exist at the fifth day after radiotherapy(P<0.05).3 Correlation analysis between ADC value and V24ADC0 has no significant correlation with V24, whereas ADC1 was positively correlated with V24(r=0.617, P=0.001<0.05). Both ADC6 and ADC13 were negatively correlated with V24(r=-0.685,-0.896, P=0.000, 0.000 <0.01).Conclusion: The results of this animal experimental study show that single large fraction dose radiotherapy can inhibit the growth of xenograft. ADC values may change significantly at the early stage after radiotherapy, which indicates that diffusion-weighted magnetic resonance imaging has huge potential in the prediction and evaluation of radiation sensitivity. |
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