Cultured tumor cells show a marked increase in deoxyglucose uptake as early as 3 h after single high-dose irradiation, reflecting hyperacute response of the cells to noxious intervention. To evaluate the hyperacute effect of high-dose irradiation on tumor glucose metabolism in vivo, we measured 2-[18F]fluoro-2-deoxy-D-glucose (FDG) tumor uptake before and immediately after stereotactic radiosurgery.
Methods: A total of 19 brain tumors (17 metastatic and 2 primary, a meningioma and a central neurocytoma) in eight patients were treated with stereotactic radiosurgery. The received dose was between 24 and 32 Gy delivered to the central target point in the tumor. FDG PET was performed within 1 wk before radiosurgery and again 4 h after treatment. The net influx constant (Ki) was calculated on a pixel-by-pixel basis using graphical analysis, and the Ki ratio of tumor to ipsilateral cerebellum was used as an index of FDG uptake of the tumor.
Results: Eighteen of 19 irradiated tumors, all metastatic tumors and the meningioma, showed a 29.7% +/- 14.0% increase in the Ki ratio, which was significantly higher than that of nonirradiated tumors (4.1% +/- 3.6%, n = 8, P < 0.0001, analysis of variance). In metastatic tumors, an increase in the Ki ratio was significantly correlated with a decrease in the size of the irradiated tumors, as revealed by follow-up with CT or MRI (r = 0.61, P = 0.012, simple regression). The meningioma did not show a significant decrease in size, probably due to the short follow-up period. The central neurocytoma did not show any change in the Ki ratio or in tumor size.
Conclusion: Serial FDG PET could be a potential tool for predicting the outcome of radiosurgery for brain tumors by detecting hyperacute changes in tumor glucose metabolism.