18F-FDG PET/CT metabolic parameters for predicting malignancy degree of thymus epithelial tumors
Objective To investigate the value of 18F-FDG PET/CT metabolic parameters for predicting malignancy degree of thymus epithelial tumors(TET).Methods Data of 95 TET patients confirmed by pathology were retrospectively analyzed.The histological types(low-risk thymoma,high-risk thymoma,thymic cancer)and clinical stages(stage Ⅰ-Ⅳ)of TET were evaluated according to pathological findings.Based on 18F-FDG PET/CT,the maximum standard uptake value(SUVmax)and the peak standard uptake value(SUVpeak)of origical tomors,the ratio of SUVmax to the mean standard uptake value of mediastinal blood pool,i.e.target-to-background ratio(TBR)were calculated.Taking SUV=2.5 and 40％SUVmax as thresholds,the total lesion glycolysis(TLG2.5,TLG40％)and metabolic tumor volume(MTV2.5,MTV40％)were obtained,respectively.Metabolic parameters of TET were compared among different histological types and clinical stages.Receiver operating characteristic(ROC)curves of the above metabolic parameters being significantly different in pairwise comparisons were drawn,and the area under the curve(AUC)were calculated to evaluate the efficacy for predicting for histological type of TET.Results Among 95 cases,low-risk thymoma,high-risk thymoma and thymic cancer were found in 27,15 and 53 cases,including 28 cases of stage Ⅰ,8 cases of stage Ⅱ,12 cases of stage Ⅲ and 47 cases of stage Ⅳ.Significant differences of SUVmax,SUVpeak and TBR were among different histological types TET(all P＜0.05).TLG2.5 and MTV2.5 of high-risk thymoma and thymic cancer were higher than those of low-risk thymoma(all P＜0.05),and TLG40％of thymic cancer was higher than that of low-risk thymoma(P＜0.05).No significant difference of other metabolic parameters was found(all P＞0.05).SUVmax,SUVpaak,TBR,TLG2.5,TLG40％and MTV2.5 of stage ⅣTET were higher than those of stage Ⅰ TET(all P＜0.05),and TLG2.5 of stage Ⅲ TET was higher than that of stage ⅠTET(P＜0.05).There was no significant difference of other metabolic parameters among TET among different clinical stages(all P＞0.05).AUC of SUVmax,SUVpeak and TBR for predicting low-risk and high-risk thymoma was 0.857,0.840 and 0.857,for predicting high-risk thymoma and thymic cancer was 0.769,0.758 and 0.755,respectively.Conclusion 18F-FDG PET/CT metabolic parameters could effectively predict malignancy degree of TET.
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