This study aimed to define the potential of 1-(11)C-acetate PET, compared with (18)F-FDG, in detecting meningiomas and monitoring the effect of gamma-knife radiosurgery.
Methods: Twenty-two patients with the neuroradiologic diagnosis of meningioma were examined by 1-(11)C-acetate and (18)F-FDG PET on the same day. There were 12 cases of histopathologically proven meningioma (8 grade I, 2 grade II, and 2 grade III), 1 of tuberculous granuloma, and 1 of degenerative tissue. 1-(11)C-acetate PET scans of fasting patients were obtained 10 min after intravenous administration of 740 MBq of 1-(11)C-acetate. (18)F-FDG PET was performed at 2 h after 1-(11)C-acetate scanning. The PET images were evaluated by a qualitative method and semiquantitative analysis using standardized uptake value and tumor-to-cortex ratio.
Results: The (18)F-FDG PET study revealed a hypometabolic focus in 17 meningiomas (8 grade I, 1 grade II, and 8 unknown grade) and hypermetabolism in 1 grade II and 2 grade III meningiomas. High uptake of 1-(11)C-acetate was observed in all 20 meningiomas, in contrast to the low uptake in surrounding normal brain tissue, allowing a clearer demarcation of the tumor boundary than that provided by (18)F-FDG. Dissociation of regional accumulation of 1-(11)C-acetate and (18)F-FDG within the tumor was also noted on the coregistered images. The standardized uptake value for 1-(11)C-acetate was not different from that for (18)F-FDG (mean +/- SD, 3.16 +/- 1.75 vs. 3.22 +/- 1.50, P = 0.601), but the tumor-to-cortex ratio for 1-(11)C-acetate was higher than that for (18)F-FDG (3.46 +/- 1.38 vs. 0.93 +/- 1.08, P < 0.005). (18)F-FDG was able to differentiate grade I from grade II-III meningiomas, whereas 1-(11)C-acetate was unable to do so. Tuberculous granuloma had a high 1-(11)C-acetate and (18)F-FDG uptake similar to that of grade II/III meningioma. Five patients received 1-(11)C-acetate and (18)F-FDG PET before and after gamma-knife surgery. 1-(11)C-acetate performed better than did (18)F-FDG in monitoring the response of tumor metabolism to radiosurgery.
Conclusion: 1-(11)C-acetate was found to be useful for detecting meningiomas and evaluating the extent of meningiomas and potentially useful for monitoring tumor response to radiosurgery. However, 1-(11)C-acetate was not useful for evaluating the tumor grade. (18)F-FDG was found to be less useful than 1-(11)C-acetate for evaluating the extent of meningiomas and the response to radiosurgical treatment but may be useful for differentiating benign from malignant meningiomas. (18)F-FDG and 1-(11)C-acetate are complementary for assessing diverse cell metabolism of meningioma.