Comparison of the prognostic values of 68Ga-DOTANOC PET/CT and 18F-FDG PET/CT in patients with well-differentiated neuroendocrine tumor.

PURPOSE: To determine the prognostic value of (68)Ga-DOTANOC PET/CT in patients with well-differentiated neuroendocrine tumor (NET), and to compare the prognostic value with that of (18)F-FDG PET/CT and other conventional clinicopathological prognostic factors. METHODS: Data from 37 consecutive patients (age 46.6 ± 13.5 years, 51% men) with well-differentiated NET who underwent (68)Ga-DOTANOC PET/CT and (18)F-FDG PET/CT were analyzed. All patients underwent a baseline visit with laboratory and radiological examinations. Clinical and imaging follow-up was performed in all patients. Progression-free survival (PFS) was measured from the date of the first PET/CT scan to the first documentation of progression of disease. RESULTS: (68)Ga-DOTANOC PET/CT was positive in 37 of the 37 patients and (18)F-FDG PET/CT was positive in 21. During follow-up 10 patients (27%) showed progression of disease and 27 (73%) showed no progression (24 stable disease, 3 partial response). The median follow-up was 25 months (range 2 - 52 months). Among the variables evaluated none was significantly different between the progressive disease and nonprogressive disease groups, with only SUVmax on (68)Ga-DOTANOC PET/CT being borderline significant (P = 0.073). In the univariate analysis for PFS outcome, SUVmax on (68)Ga-DOTANOC PET/CT (HR 0.122, 95% CI 0.019 - 0.779; P = 0.026) and histopathological tumor grade (HR 4.238, 95% CI 1.058 - 16.976; P = 0.041) were found to be associated with PFS. Other factors including age, sex, primary site, Ki-67 index, TNM stage, (18)F-FDG PET/CT status (positive/negative), SUVmax on (18)F-FDG PET/CT and type of treatment were not significant. In multivariable analysis, only SUVmax on (68)Ga-DOTANOC PET/CT was found to be an independent positive predictor of PFS (HR 0.122, 95% CI 0.019 - 0.779; P = 0.026). CONCLUSION: SUVmax measured on (68)Ga-DOTANOC PET/CT is an independent, positive prognostic factor in patients with well-differentiated NET and is superior to SUVmax on (18)F-FDG PET/CT and conventional clinicopathological factors for predicting PFS.

Perfusion-metabolism coupling in recurrent gliomas: a prospective validation study with 13N-ammonia and 18F-fluorodeoxyglucose PET/CT.

INTRODUCTION: We assessed the validity of "perfusion-metabolism coupling" hypothesis in recurrent glioma with 13N-ammonia (13N-NH3) PET/CT and 18F-fluorodeoxyglucose (18F-FDG) PET/CT. METHODS: Fifty-six consecutive patients (age, 38.8 ± 12.1 years; 62.5% males) with histologically proven and previously treated glioma presenting with clinical suspicion of recurrence were prospectively enrolled and evaluated with 13N-NH3 PET/CT and 18F-FDG PET/CT. PET/CT images were evaluated both qualitatively and semiquantitatively. Tumor to white matter uptake ratio (T/W) and tumor to gray matter uptake ratio (T/G) were calculated and analyzed for both the modalities. A combination of clinico-radiological follow-up, repeated imaging, and biopsy (when available) were considered as the reference standard. RESULTS: Based on the reference standard, 27/56 patients had recurrence. 13N-NH3 PET/CT and 18F-FDG PET/CT were concordant in 55/56 patients. Overall sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of 13N-NH3PET/CT were 77.8, 86.2, 84.0, 80.7, and 82.1%, respectively, and for 18F-FDG PET/CT were 77.8, 89.7, 87.5, 81.2, and 83.9%, respectively. There was excellent agreement between results of 13N-NH3 PET/CT and 18F-FDG PET/CT (ĸ = 0.964; P < 0.001). The performances of 13N-NH3 PET/CT and 18F-FDG PET/CT were not significantly different between high-grade and low-grade glioma (P = 1.000). A strong positive correlation was noted between the uptake ratios derived on the two modalities (ρ = 0.866, P < 0.001 for T/W; ρ = 0.918, P < 0.001 for T/G). CONCLUSION: A combination of 13N-NH3 PET/CT and 18F-FDG PET/CT demonstrates that perfusion and metabolism are coupled in recurrent gliomas. These tracers target two different but interrelated aspects of the same pathologic process and can be used as surrogates for each other.