Comparative diagnostic performance of ¹⁸F-FLT and ¹⁸F-FDG PET for differentiating primary CNS lymphoma from glioblastoma, IDH-wildtype.

OBJECTIVES: This study aimed to compare the diagnostic performance of 3'-deoxy-3'-¹⁸F-fluorothymidine (FLT) positron emission tomography (PET) with that of ¹⁸F-fluorodeoxyglucose (FDG) PET for differentiating primary central nervous system lymphoma (PCNSL) from glioblastoma, isocitrate dehydrogenase (IDH)-wildtype, in patients who underwent both examinations before treatment. METHODS: We retrospectively evaluated 58 patients with histologically confirmed tumors: 40 with glioblastoma, IDH-wildtype, and 18 with PCNSL. Maximum standardized uptake values of the tumors were normalized to the mean standardized uptake values of the contralateral normal-appearing brain to calculate the tumor-to-normal brain (T/N) ratio. The paired areas under the receiver operating characteristic curves (AUCs) were compared. RESULTS: FLT PET findings were positive for all tumors, whereas FDG PET findings were positive in 17 of 18 PCNSLs (94%) and 25 of 40 glioblastomas (63%). The mean FLT T/N ratio was 30.14 ± 15.02 for PCNSLs and 12.80 ± 7.37 for glioblastomas (P < 0.001), and the mean FDG T/N ratios were 3.01 ± 1.45 and 1.50 ± 1.22, respectively (P < 0.001). The AUC was 0.885 (95% confidence interval [CI], 0.794-0.976) for FLT and 0.826 (95% CI, 0.713-0.940) for FDG. Using cutoff values of 20.43 for FLT and 1.96 for FDG, the sensitivity was 77.8% and 77.8%, whereas specificity was 90.0% and 80.0%, respectively. The paired AUCs did not differ significantly (P = 0.380). CONCLUSIONS: Both FLT and FDG PET differentiated PCNSL from glioblastoma, IDH-wildtype, with no significant difference between the paired AUCs. Minimal physiological FLT uptake in the normal brain enabled conspicuous tumor visualization. FLT PET may therefore serve as a useful complementary imaging approach in selected patients for whom FDG PET is less suitable.