| Objective:To assess the diagnostic accuracy and find suitable critical value of maximum standardized uptake value(SUVmax)of 18F-FDG PET-CT for distinguishing non-small cell lung cancer (NSCLC) and pulmonary benign lesion. To correct the verification bias of sensitivity and specificity and explore the factors influenced diagnostic accuracy of it. To analyze the cost-effectiveness of PET-CT for the diagnosis ofNSCLC.Method:(1) Sixty-eight cases of NSCLC and thirty-four cases of pulmonary benign lesion examined by PET-CT were proved by surgery, biopsy, pathology or follow-up. All cases were diagnosed by SUVmax analysis, CT visual analysis, PET-CT visual analysis and PET-CT visual analysis plus SUVmax. The sensitivity, specificity, accuracy, positive predictive value, negative predictive value, Youden's index, positive likelihood ratio and negative likelihood ratio, the area under ROC curve were calculated and compared.(2) Three methods,which based on making Youden's index maximum, making false positive rate and false negative rate equal, making accuracy maximum, were used to find suitable critical value of SUVmax of 18F-FDG PET-CT for distinguishing NSCLC and pulmonary benign lesion. (3) The verification bias of the sensitivity and specificity were corrected by using maximum likelihood estimate. The cases not to be proved by "gold standard" included 625 cases of NSCLC and 332 cases of pulmonary benign lesion diagnosed by PET-CT at the same period.(4) To explore the factors of the diagnostic accuracy by using binary logistic regression and ordinal logistic regression.(5) Comparison of cost-effectiveness Of 18F-FDG PET-CT and CT in the diagnosis of NSCLC by incremental analysis and sensitivity analysisResults:(1)The sensitivity of the SUVmax analysis, CT visual analysis, PET-CT visual analysis and PET-CT visual analysis plus SUVmax were 91.2%,83.8%,89.7%,89.7%, respectively. The specificity of it were 55.9%,55.9%,55.9%,64.7%, respectively. The Youden's index of it were 0.471,0.397,0.456,0.544, respectively. The accuracy of it were 79.4%, 74.5%,78.4%,81.4%, respectively. The positive predictive values of it were 80.5%,79.2%,80.3%,83.6%, respectively. The negative predictive values of it were 76.0%,63.3%,73.1%,75.9%, respectively. The positive likelihood ratio of it were 2.068,1.900,2.027,2.541, respectively. The negative likelihood ratio of it were 0.157,0.290,0.184,0.159, respectively. empirical area under the ROC curve of it were 0.7946,0.7814,0.8227,0. 8722, respectively. The area under the fitted smooth ROC curve, based upon binormal model were 0.7973,0.8059,0.9055,0.9172, respectively. The area of empirical and the Fitted smooth ROC curve is in statistical significant(P<0.05),compared with the area under the reference line. The difference of the area under ROC curve of the method of PET-CT visual analysis plus SUVmax was in statistical significant(P<0.05) compared with the methods of SUVmax analysis and CT visual analysis(2) The SUVmax distribution of NSCLC and pulmonary benign lesion was skewness distribution. The means±standard deviation of SUVmax of NSCLC and pulmonary benign lesion were 8.6±5.3,3.8±3.7 respectively.The median(quartilerange) was 2.3(5.2),7.2(6.1),respectively. The difference of SUVmax between NSCLC and pulmonary benign lesion was in statistical significant (P<0.001). The means±standard deviation of SUVmax of lung squamous cell carcinoma and lung adenocarcinoma were 9.5±4.5,7.2±6.2 respectively. The median(quartile range) were 8.8(5.1),5.5(6.3)respectively. The difference of SUVmax between lung squamous cell carcinoma and lung adenocarcinoma was not in statistical significant (P=0.327). The Spearman correlation coefficient between SUVmax and tumor size was 0.632(P<0.001). The optimal critical value of SUVmax was 2.8,5.5,2.8 respectively according to the rule of making Youden's index maximum, making the false positive rate and false negative rate equal,making the accuracy maximum.(3) After correcting verification bias, the corrected sensitivity of the PET-CT visual analysis was 84.9%, the corrected specificity of it was 15.1%.(4)Tumor volumn was a factor affected the specificity of SUVmax analysis and also a factor affected the sensitivity of PET-CT visual analysis and PET-CT visual analysis plus SUVmax, using binary logistic regression analysis. The tumor size was a factor affected ROC curve of CT visual analysis (5-category scale:normal, benign, probably benign, suspicious, malignant) and PET-CT visual analysis (5-category scale: normal, benign, probably benign, suspicious, malignant).(5) PET-CT and CT diagnostic cost-effectiveness ratio were 6242.62RMB per cases and 322.11 RMB percases respectively. Incremental ratio of diagnostic cost-effectiveness was 90610 RMB per cases. Incremental ratio of diagnostic cost-effectiveness was 40271 RMB per cases with change of the sensitivity for the PET-CT.Conclusions:(1) There was a positive correlation between SUVmax and Tumor size. The SUVmax of NSCLC was higher than pulmonary benign lesion. The difference of SUVmax between lung squamous cell carcinoma and lung adenocarcinoma was not in statistical significant (P=0.327). The optimal critical value of SUVmax was 2.8.(2) The comparisons of the diagnostic accuracy among SUVmax analysis, CT visual analysis, PET-CT visual analysis and PET-CT visual analysis plus SUVmax showed that the sensitivity of SUVmax analysis (semi quantity) was the maximum, the specificity of CT visual analysis (visual analysis) was the maximum, the area under the ROC curve of PET-CT visual analysis plus SUVmax (visual analysis plus semi quantity)was the maximum.(3) The effect of verification bias overestimated sensitivity and specificity for diagnostic accuracy of 18F-FDG PET-CT in distinguishing NSCLC and pulmonary benign lesion.(4) The tumor size and volume were the factors influencing the diagnostic accuracy of 18F-FDG PET-CT in distinguishing NSCLC and pulmonary benign lesion.(5) The diagnostic cost-effectiveness ratio and incremental ratio of diagnostic cost-effectiveness were high for the PET-CT.
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