Relation between nodule size and 18F-FDG-PET SUV for malignant and benign pulmonary nodules.

: The most common semiquantitative method of evaluation of pulmonary lesions using F-18-FDG PET is FDG standardized uptake value (SUV). An SUV cutoff of 2.5 or greater has been used to differentiate between benign and malignant nodules. The goal of our study was to investigate the correlation between the size of pulmonary nodules and the SUV for benign as well as for malignant nodules. Methods: Retrospectively, 173 patients were selected from 420 referrals for evaluation of pulmonary lesions. All patients selected had a positive CT and PET scans and histopathology biopsy. A linear regression equation was fitted to a scatter plot of size and SUVmax for malignant and benign nodules together. A dot diagram was created to calculate the sensitivity, specificity, and accuracy using an SUVmax cutoff of 2.5. Results: The linear regression equations and (R-2)s as well as the trendlines for malignant and benign nodules demonstrated that the slope of the regression line is greater for malignant than for benign nodules. Twenty-eight nodules of group one (<= 1.0 cm) are plotted in a dot diagram using an SUVmax cutoff of 2.5. The sensitivity, specificity, and accuracy were calculated to be 85%, 36% and 54% respectively. Similarly, sensitivity, specificity, and accuracy were calculated for an SUVmax cutoff of 2.5 and found to be 91%, 47%, and 79% respectively for group 2 (1.1-2.0 cm); 94%, 23%, and 76%, respectively for group 3 (2.1-3.0 cm); and 100%, 17%, and 82%,, respectively for group 4 (> 3.0 cm). The previous results of the dot diagram indicating that the sensitivity and the accuracy of the test using an SUVmax cutoff of 2.5 are increased with an increase in the diameter of pulmonary nodules. Conclusion: The slope of the regression line is greater for malignant than for benign nodules. Although, the SUVmax cutoff of 2.5 is a useful tool in the evaluation of large pulmonary nodules (>1.0 cm), it has no or minimal value in the evaluation of small pulmonary nodules (<= 1.0 cm).