How useful is FDG PET for the evaluation of primary and metastatic brain tumors?
FDG PET generally has low sensitivity for early detection of primary or metastatic brain tumors, given the normal high level of FDG uptake in the brain. For this reason, MRI is predominantly utilized for diagnostic assessment of the brain in cancer patients. However, FDG PET is useful to better characterize brain tumor biology, because more aggressive higher grade tumors will in general have greater degrees of FDG uptake than more indolent lower grade tumors. Furthermore, FDG PET is most useful to differentiate tumor recurrence from radiation necrosis in the surgical bed. Typically, active tumor is easier to detect in the setting of background hypometabolism related to treatment effects.