The Role of Dual-Phase FDG PET/CT in the Diagnosis and Follow-Up of Brain Tumors

Abstract

OBJECTIVE. FDG PET/CT of brain tumors is limited by background activity. Dual-phase FDG PET/CT can eliminate this limitation and allow discernment of viable tumors. Our aim was to assess the diagnostic capability of dual-phase FDG PET/CT qualitatively and quantitatively and to determine cutoff values for dual-phase FDG PET/CT in brain tumor imaging. MATERIALS AND METHODS. Retrospectively, 51 malignant brain tumors were evaluated with dual-phase FDG PET/CT in 32 patients. Acquisitions were performed 30 minutes (time 1) and 3 hours (time 2) after administration of 10 mCi (370 MBq) FDG and 6 hours of fasting. Two observers independently and qualitatively evaluated lesions. A weighted Cohen kappa was used to calculate interrater reliability and accuracy. Quantitatively, maximum standardized uptake value (SUV_max) was measured in the lesions, contralateral white matter (CWM), contralateral caudate nucleus head, and ipsilateral cerebellar cortex (CC). Lesion-to-CWM SUV_max, lesion-to-contralateral caudate nucleus head SUV_max, and lesion-to-ipsilateral CC SUV_max ratios at time 1 and time 2 were calculated. ROC analysis was used to determine optimum cutoff values, and AUC ratios were compared among quantitative parameters. Lesion outcome was determined by pathologic results (available in 15 lesions), lesion stability on serial MRI examinations (representing nonviable tumor), or decreased tumor size on serial MRI examinations after new treatment (representing viable tumor). RESULTS. Thirty-seven viable and 14 nonviable lesions were evaluated. Qualitatively, the diagnostic accuracy (first observer: κ = 0.45 to κ = 0.59; second observer: κ = 0.41 to κ = 0.66) and interrater reliability (at time 1: κ = 0.51; at time 2: κ = 0.83) improved with delayed imaging. AUC and ROC analysis showed comparably high sensitivity, specificity, and accuracy profiles for early and delayed dual-phase FDG PET/CT. Some of the proposed cutoff values were as follows: lesion SUV_max at time 1, 7.20 (sensitivity, 89.2%; specificity, 85.7%); lesion SUV_max at time 2, 7.80 (sensitivity, 97.3%; specificity, 71.4%); lesion-to-CWM SUV_max at time 1, 2.05 (sensitivity, 78.4%; specificity, 92.9%); and lesion-to-CWM SUV_max at time 2, 2.36 (sensitivity, 81.1%; specificity, 85.7%). CONCLUSION. Dual-phase FDG PET/CT improves lesion detection and diagnostic accuracy in malignant brain tumors.

Keywords: FDG PET/CT; brain; delayed imaging; dual phase; tumor.