Abstract
We studied 15 patients clinically suspected to have recurrent brain tumor or radiation injury, using positron emission tomography (PET) with 18F-fluorodeoxyglucose (18FDG) and L-methyl-11C-methionine (11C-Met). PET with 11C-Met (Met-PET) clearly delineated the extent of recurrent brain tumor as focal areas of increased accumulation of 11C-Met, and was useful for early detection of recurrent brain tumor. PET with 18FDG (FDG-PET) showed focal 18FDG-hypermetabolism in one patient with malignant transformation of low grade glioma, and demonstrated its usefulness for evaluation of malignant transformation. 18FDG-hypometabolism was observed in all patients with radiation injury, but was also found in one patient with recurrent malignant brain tumor. 11C-Met uptake in 3 patients with radiation injury was similar to that of the normal cortical tissue. FDG-PET can be used to initially exclude recurrent brain tumor which is seen as 18FDG-hypermetabolism. The combined use of Met-PET in addition to FDG-PET can improve the accuracy of differentiation of recurrent brain tumor with 18FDG-hypometabolism from radiation injury.