An Experimental Study Of DCE-MRI Assessment Of Cortical Bone Changes After Radiotherapy For VX2 Malignant Bone Tumors

OBJECTIVE:To assess the value of quantitative DCE-MRI parameters in differentiating the bone cortical infiltration zone of malignant bone tumors from the normal bone cortical zone.Methods:Forty New Zealand Large White rabbits were implanted with VX2 tumor strain in the right tibia to establish a malignant bone tumor model.Conventional MRI and DCE-MRI were performed 2 weeks after the model was constructed.The right tibia was cut into sagittal tomographic sections using a hard tissue slicer,and then the bone cortical area was selected for histological sectioning,HE staining and immunohistochemical examination,and the results obtained from immunohistochemical examination were recorded.The extent of infiltration in the bone cortical area was determined under the microscope,and the DCE images of the corresponding area were outlined and quantitatively analyzed,and the K^trans,K_ep,V_e,and i AUC values of the infiltrated and normal areas were automatically calculated by the post-processing workstation.Point-to-point comparison of pathology and MR images was performed.Independent samples t-test was used to compare the differences between the indicators of the two regions.The subject operating characteristic curve(ROC)was plotted and the diagnostic efficacy of different parameters was determined according to the area under the curve(AUC),and finally the quantitative parameter with the highest efficacy was derived as the monitoring index.RESULTS:The K^trans,V_e,K_ep,and i AUC values were all higher in the bone cortical infiltrated area than in the normal bone cortical area,and the difference between the two groups was statistically significant for K^trans,V_e,and i AUC values(p<0.05),while the difference between the two groups was not statistically significant for K_ep values(p=0.069).K^transvalues were the most accurate in distinguishing the different areas(AUC=0.824).0.824).statistically significant correlations were found between MVD counts and K^trans and i AUC values(r values 0.803 and 0.359,respectively,p<0.05),while the degree of VEGF expression was positively correlated with K^trans,V_e,and i AUC values(r values 0.324,0.292,and 0.341,respectively,p<0.05).CONCLUSION:The quantitative parameters of DCE-MRI can be used to assess the cortical infiltration zone of malignant bone tumors.K^trans has the highest efficacy in distinguishing different regions.OBJECTIVE: To compare the changes of quantitative parameters of DCE-MRI and their correlation with immunohistochemical indexes after radiotherapy to the bone cortical infiltration area of VX2 malignant bone tumors,and to assess the value of DCE-MRI in monitoring the efficacy of early radiotherapy for malignant bone tumors.METHODS: After 2 weeks of constructing the animal model of VX2 malignant bone tumor,a total of 2 groups were divided into pre-treatment group(n=10),treatment group(n=15),and control group(n=15)by random sampling.The pre-treatment group was executed for pathological examination after MRI scan on day 1 2 weeks after tumor implantation,and the results were used as the baseline parameters for post-treatment changes;the treatment group was scanned 1 day before and 3 days after receiving radiotherapy,while the control group did not receive any treatment and underwent MRI examination at the same time as the treatment group.The quantitative DCE-MRI parameters of the bone cortical infiltration area and the immunohistochemical indexes(MVD count,Ki67 index and VEGF expression level)of the corresponding area were obtained by pathology-imaging point-to-point method.The changes between the quantitative parameters before and after radiotherapy and the values before treatment and their correlation with the immunohistochemical indexes were statistically analyzed in the treated and control groups of the bone cortical infiltrated area,while the subject operating characteristic curve(ROC)was drawn,and the diagnostic efficacy of different parameters was determined according to the area under the curve(AUC).RESULTS:(1)Comparison of quantitative parameters of DCE-MRI in the bone cortical infiltrate area after radiotherapy in the treatment,control and pre-treatment groups: in the comparison between the treatment and pre-treatment groups,the values of K^trans,V_e and i AUC decreased compared with those before,and the differences between the groups were statistically significant(p<0.05),while the values of K_ep increased compared with those of the pre-treatment group,and the differences between the groups were not statistically significant(p=0.480).In the comparison between the control group and the pre-treatment group,K^trans,K_ep and i AUC values were all increased compared with the pre-treatment group,and only the difference between the i AUC values was statistically significant(p<0.05),while V_e values were decreased compared with the pre-treatment group,and the difference between the groups was not statistically significant(p = 0.500).(2)Comparison of immunohistochemical indexes in the bone cortical infiltration area after radiotherapy between the treatment group,control group and pre-treatment group: MVD count: in the comparison between the treatment group and pre-treatment group,MVD count,VEGF expression degree and Ki67 index were all reduced compared with those before,and the differences between the groups were statistically significant(p<0.05);in the comparison between the control group and pre-treatment group,MVD count,VEGF expression degree,Ki67 index were all reduced compared with those before,and the differences between the groups were statistically significant(p<0.05).In the comparison between the control group and the pre-treatment group,MVD count,VEGF expression and Ki67 index were all reduced,but the differences between the groups were not statistically significant(p=0.329,0.697,0.823).(3)Correlation between quantitative parameters of DCE-MRI and immunohistochemical indexes in the bone cortical infiltration area after radiotherapy in the treatment and control groups: statistically significant correlations were found between MVD counts and K^trans,V_e,and i AUC values(r values were 0.786,0.344,and 0.587,respectively,p < 0.05),while no statistical correlation was found between MVD counts and K_ep values(r values were 0.169,p=0.309);there was a positive correlation between the degree of VEGF expression and K^trans,V_e,and i AUC values(r values of 0.496,0.522,and 0.376,respectively,p<0.05),and no statistical correlation between the degree of VEGF expression and K_ep values(r values of-0.079,respectively,p=0.638);the correlation between Ki67 index and K^trans,V_e and i AUC values were positively correlated(r-values were 0.385,0.395 and 0.385,respectively,p<0.05),and there was no statistical correlation between Ki67 index and K_ep values(r-values were 0.143,respectively,p=0.391).CONCLUSION: The quantitative parameters K^trans,V_e and i AUC values of DCE-MRI decreased after radiotherapy and differed statistically from the pre-treatment group,while both correlated with MVD counts,Ki67,and VEGF expression levels.K^trans was the most effective in monitoring post-radiation changes.It can help to accurately reflect the tumor hemodynamic changes after radiotherapy,and provide a more early and accurate judgment basis for the formulation and adjustment of radiotherapy regimen.