INDEPENDENT TL-201 ACCUMULATION AND FLUORINE-18-FLUORODEOXYGLUCOSE METABOLISM IN GLIOMA

SPECT with (TI)-T-201 is an effective procedure for evaluating the mal ignancy of glioma. Our goal was to investigate the diagnostic relevanc e of both (TI)-T-201 SPECT and [F-18] fluorodeoxyglucose (FDG) PET and the relation between (TI)-T-201 uptake and glucose metabolism in glio ma using comparative SPECT and PET studies, Methods: Thallium-201 SPEC T and FDG dynamic PET studies were performed in 20 patients with untre ated glioma (5 with glioblastoma, 5 with anaplastic glioma, 10 with lo w-grade glioma). Thallium-201 uptake in the tumor was estimated using the (TI)-T-201 index, defined as the ratio of (TI)-T-201 uptake in the tumor to that in the contralateral normal brain on SPECT images obtai ned 15 min after intravenous injection. We measured regional glucose m etabolic parameters, including rate constants and regional cerebral me tabolic rate of glucose utilization (rCMRgI), in the tumor. We then co mpared the regional (TI)-T-201 index and glucose metabolic parameters with the histologic characteristics, malignancy and computed tomograph ic/magnetic resonance imaging findings. In addition, we investigated t he correlation between the (TI)-T-201 index and glucose metabolic para meters. Results: Thallium-201 SPECT showed abnormal (TI)-T-201 uptake in all patients with glioblastoma and anaplastic glioma. Thallium-201 indices of glioblastoma (202.6 +/- 22.1 %) and anaplastic glioma (176. 6% +/- 26.6%) were significantly higher than that for low-grade glioma (106.7% +/- 13.8%). The rCMRgI value of glioblas toma (17.6 +/- 3.5 m u mole/100 g/min) was also significantly higher than that for low-grad e glioma (10.8 +/- 4.5 mu mole/100 g/min), although rCMRgI showed a la rge variability in both high- and low-grade glioma. Rate constants of FDG kinetics had no correlation with histological grade of glioma, Som e patients with high-grade glioma, however, showed false-negative resu lts with FDG-PET because of high normal brain uptake of FDG. Conversel y, most low-grade glioma could not be localized by (TI)-T-201 SPECT. T here was no correlation between the (TI)-T-201 index and glucose metab olic parameters. Conclusion: Thallium-201 indices and rCMRgI values fo r glioblastoma were higher than those for low-grade glioma. Thallium-2 01 uptake in the tumor may be independent of increased glucose transpo rt or metabolism. Thallium-201 SPECT and FDG-PET are complementary in the diagnosis of glioma, although (TI)-T-201 SPECT is more significant ly correlated with the malignancy of glioma.