SU-FF-T-366: Radiation Dose Response Curve of Human Cerebral Cortex Measured with [F-18]-FDG and [O-15]-H2O PET Imaging

Purpose: To study radiotherapy (RT)‐induced dose‐dependent functional changes in the human cerebral cortex region using serial 18 F‐FDG and 15 O‐ H 2 O PETimaging before and after RT. Method and Materials: Eleven human subjects were enrolled in an IRB‐approved prospective study to quantitatively measure changes in post‐RT brain function. 18 F‐FDG and 15 O‐H 2 O PETimages were taken pre‐RT, and again at 3 weeks and 6 months post‐RT, to quantitatively assess for RT‐induced changes in relative metabolism and relative regional blood flow (RBF). The 3 week and 6 month follow‐up evaluations were available for 7 and 6 patients, respectively. Follow‐up images were registered to their corresponding pre‐RT baseline images, as well as to the treatment planning CT/MRI scans, for quantitative analysis. Relative changes in regional 18 F‐FDG and 15 O‐H 2 O PET activities were related to regional RT dose. Regions of the cerebral cortex receiving 40–50Gy. Initially, relative RBF increases (generally <10%) were observed on 15O‐H2O PETimaging (3 week follow‐up), but were much less significant at the 6‐month follow‐up. Conclusion: The response of cerebral cortex tissue to RT can be detected, in a dose‐dependent manner, using 18 F‐FDG PET. The magnitude of the changes, however, was typically small (<8%). Initially there were increases in relative RBF, but no discernable changes were seen at 6 months followup in 15 O‐H 2 O PET. Further studies are needed for more conclusive results. Results from neuropsychological testing will be used to assess the potential clinical impact of the changes measured by PET.