A Comparative Study Of IVIM-DWI And Pathology For Evaluation After Radiotherapy On Rabbit VX2 Bone Tumor Models

Objective:To compare the changes in quantitative parameters of intravoxel incohorent movement diffusion weighted imaging（IVIM-DWI）before and after radiotherapy for rabbit VX2 malignant bone tumors,and to evaluate the correlation between tumor cell density,MVD count,and VEGF expression.To explore the value of IVIM-DWI in the noninvasive evaluation of the early changes in the efficacy of early radiotherapy for malignant bone tumors and to reflect the microvascular changes of malignant bone tumors.Methods:Rabbit VX2 malignant bone tumor models were established and randomly divided into an experimental group（n=15）and a control group（n=15）after 2 weeks.The experimental group underwent radiation therapy（10 Gy/time）and performed IVIM-DWI scans 1 day before and 3 days after radiotherapy.The control group received no treatment,and IVIM-DWI scans were performed concurrently with the experimental group.The Siemens post-processing software was used to quantitatively analyze the scanned images to obtain a series of observation index parameters of the tumor solid area and necrotic area:apparent diffusion coefficient（ADC）,true diffusion coefficient（D）,perfusion-related diffusion coefficient（D^*）,perfusion fraction（f）.After the second IVIM-DWI scan,the experimental rabbits and control rabbits were sacrificed,After the second IVIM-DWI scan,the model rabbits were sacrificed,and tumor-bearing bone specimens were taken out for sectioning,HE staining and immunohistochemical examination（including MVD and VEGF）.Statistical analysis of the changes in IVIM-DWI quantitative parameters before and after radiotherapy in the experimental group and in the control group over the same period,analysis of the diagnostic efficacy of each quantitative parameter index,and analysis of the correlation between IVIM-DWI quantitative parameters and tumor cell density,MVD count,and VEGF expression.Results:1.Comparison of IVIM-DWI quantitative parameter indexes before and after radiotherapy in the tumor solid area and necrotic area in experimental group and control group:In the experimental group,the ADC value and D value of tumor solid area and necrosis area after radiotherapy were increased compared with those before radiotherapy,and the differences were statistically significant（P<0.05）.After radiotherapy in the experimental group,the D^*value and f value of tumor solid area decreased compared with before radiotherapy,and the differences were statistically significant（P<0.05）.There was no significant difference in D^*value and f value before and after radiotherapy in tumor necrosis area of experimental group（P=0.788,0.916）.In the control group,the ADC value and D value of the tumor solid area during the same period were lower than those after radiotherapy significantly（P<0.05）.In the control group,the ADC value and D value of the tumor necrosis area during the same period after radiotherapy were significantly increased compared with the same period before radiotherapy（P<0.05）.In the control group,the D^*value and f value of the solid tumor area before radiotherapy were the same as those after radiotherapy（P=0.526,0.886）.In the control group,the D^*value and f value of the tumor necrosis area before radiotherapy were the same as those after radiotherapy（P=0.563,0.238）.After radiotherapy in the experimental group,the ADC value and D value of the solid area increased compared with the control group,and the D^*value and f value decreased compared with the control group,the difference was statistically significant（P<0.05）.After radiotherapy in the experimental group,the D value of the necrotic area increased compared with the control group,and the f value decreased compared with the control group,the differences were statistically significant（P<0.05）.The ADC value and D^*value of the necrotic area in the experimental group after radiotherapy were not significantly different from those in the control group（P=0.054,0.353）.2.Comparison of the areas under the ROC curve of IVIM-DWI quantitative parameter indexes before and after radiotherapy in the tumor solid area and necrotic area of the experimental group and the control group:In the experimental group,the areas under the curve（AUCs）of ADC value,D value,D^*value,and f value were 0.911,0.924,0.729,and0.653,respectively,before and after the radiotherapy in the tumor solid area.The D value has the highest diagnostic efficiency.D=784.90×10^-6 mm²/s can be used as a threshold for the differential diagnosis experimental group before and after radiotherapy in the solid area of the tumor.The sensitivity and specificity were 93.30%and 86.70%,respectively.The difference between D value and ADC value in each index change of tumor necrosis area before and after radiotherapy in the experimental group was statistically significant.The AUCs were 0.960 and 0.956,respectively.The D value had the highest diagnostic efficiency.D=973.00×10^-6 mm²/s can be used as a threshold for the differential diagnosis experimental group before and after radiotherapy in the necrosis area of the tumor.Both sensitivity and specificity were 93.30%.In the control group,the AUCs of ADC value and D value were 0.822 and 0.791,respectively.The ADC value had the highest diagnostic efficiency.ADC=677.50×10^-6 mm²/s can be used as a threshold for the differential diagnosis control group before and after radiotherapy in the solid area of the tumor.Its sensitivity and specificity were 80.00%and 86.70%,respectively.The difference between ADC value and D value in the changes of various indexes before and after radiotherapy in the tumor necrosis area of the control group was statistically significant.The AUCs were 0.942 and 0.933,respectively,and the ADC value had the highest diagnostic efficacy.ADC=970.90×10^-6 mm²/s can be used as a threshold for the differential diagnosis control group before and after radiotherapy in the necrosis area of the tumor.The sensitivity and specificity were 93.30%and 86.70%,respectively.In the comparison of the indexes in the solid area of the tumor between the experimental group and the control group after radiotherapy,the AUCs of ADC value,D value,D^*value,and f value were 0.947,0.964,0.707,and 0.720,respectively.D value had the highest diagnostic efficacy.D=743.50×10^-6 mm²/s can be used as the threshold for the change of the solid area of the tumor in the differential diagnosis experimental group after radiotherapy and the control group during the same period.Both sensitivity and specificity were 93.30%.In the comparison between the indexes in the tumor necrosis area of the experimental group and the control group after radiotherapy,the difference between the D value and the f value was statistically significant,and the AUCs were0.698 and 0.727,respectively.f=34.50%can be used as the threshold for the change of the necrotic area of the tumor in the differential diagnosis experimental group after radiotherapy and the control group during the same period.The sensitivity and specificity were 53.30% and 80.00%,respectively.3.Comparison of the tumor cell density,MVD count,and VEGF expression in the solid and necrotic areas of the two groups after radiotherapy:the average value of the cell density in the solid and necrotic areas of the experimental group after radiotherapy were（11.04±2.26）%and（4.34±1.63）%,respectively.The average cell density of the tumor solid area and necrotic area during the same period after the radiotherapy in the control group were（20.25±2.28）%and（5.38±1.25）%,respectively.The cell density was significantly reduced compared with the control group over the same period（P<0.05）.The MVD counts of the solid and necrotic areas of the experimental group after radiotherapy were 25.33±8.94 and 13.40±8.98,respectively,and the MVD counts of the control group during the same period after the radiotherapy were 36.00±15.09 and16.20±8.80,respectively.Compared with the control group,the difference was statistically significant（P<0.05）,and there was no statistically significant difference between the two groups of tumor necrosis areas（P﹥0.05）.The expression of VEGF in the solid area of the tumor in the experimental group and the control group after radiotherapy was 4.27±1.49 and 7.00±3.32,respectively.The expression of VEGF in the solid area of the experimental group after radiotherapy decreased compared with the control group at the same period,and the difference was statistically significant（P<0.05）.The expression of VEGF in the tumor necrosis area of the experimental group and the control group was 2.67±1.40 and 3.80±1.74 respectively,and there was no significant difference between the two groups in the tumor necrosis area（P﹥0.05）.4.Correlation between quantitative parameters of IVIM-DWI and tumor cell density,MVD count,and VEGF expression in experimental and control groups after radiotherapy:（1）After radiotherapy in the experimental group,the D value in the solid area was negatively correlated with cell density（r=-0.757,P<0.05）,and the D value in the necrotic area was negatively correlated with cell density（r=-0.782,P<0.05）;In the experimental group,the ADC value in the solid area was negatively correlated with cell density after radiotherapy（r=-0.630,P<0.05）,and the ADC value in the necrotic area was negatively correlated with cell density（r=-0.750,P<0.05）;In the control group,the D value of the solid area was negatively correlated with cell density（r=-0.833,P<0.05）,and the D value of the necrotic area was negatively correlated with cell density（r=-0.666,P<0.05）;In the control group,the ADC value in the solid area was negatively correlated with cell density（r=-0.818,P<0.05）,and the ADC value in the necrotic area was negatively correlated with cell density（r=-0.653,P<0.05）.（2）After the radiotherapy in the experimental group,the f value of the solid area was positively correlated with the MVD count（r=0.878,P<0.05）,and the f value of the necrotic area was positively correlated with the MVD count（r=0.766,P<0.05）;In the control group,the f value of the solid area was positively correlated with the MVD count（r=0.738,P<0.05）,and the necrotic area f value was positively correlated with the MVD count（r=0.832,P<0.05）.（3）In the experimental group,the f value of the solid area was positively correlated with the expression of VEGF（r=0.855,P<0.05）,and the f value of the necrotic area was positively correlated with the expression of VEGF（r=0.896,P<0.05）;In the control group,the f value of the solid area was positively correlated with VEGF expression（r=0.861,P<0.05）,and the necrotic area f value was positively correlated with VEGF expression（r=0.688,P<0.05）.Conclusion:The D value of IVIM-DWI quantitative index has a significant negative correlation with the cell density of VX2 malignant bone tumors,which can best reflect the tumor cell density;There is a positive correlation between f value and MVD count and VEGF expression,which can reflect the tumor angiogenesis status.Therefore,IVIM-DWI can quantitatively evaluate the early curative effect of bone tumors after radiotherapy from the aspects of tumor cell density and microvessels,and provide a basis for clinical formulation and adjustment of treatment plans.