Highlights•[18F]FDG-PET can be used to monitor changes in glucose metabolism by most brain regions before and after IMPT in NPC.•Three months after IMPT for NPC, a significant increases in the uptake of [18F]FDG by most brain regions was observed.•A negative correlation was shown between FDG uptake and radiation dose in several brain regions.•Changes in the SUV appear to be dependent on the radiation dose in some brain regions.