Evaluation of children with craniopharyngioma using carbon-11 methionine PET prior to proton therapy.

BACKGROUND: Fluorine-18 ((18)F) fluorodeoxyglucose (FDG) positron emission tomography (PET) is limited in its evaluation of brain tumors due to the high basal activity of the cerebral cortex and white matter. Carbon-11 methionine ((11)C MET) has little uptake under normal conditions. We prospectively investigated the uptake of (18)F FDG and (11)C MET PET in patients with craniopharyngioma prior to proton therapy.
METHODS: Ten patients newly diagnosed with craniopharyngioma underwent PET imaging using (18)F FDG and (11)C MET. PET and MRI studies were registered to help identify tumor volume. Measurements of maximum standardized uptake value (SUV(max)) were taken of the tumor and compared with noninvolved left frontal background white matter using a paired t-test. Uptake was graded using a 4-point scale.
RESULTS: Median patient age was 9 years (range 5-19). Seven patients were diagnosed by pathology, 1 by cyst fluid aspiration, and 2 by neuroimaging. Median FDG SUV(max) for tumor and background were 2.65 and 3.2, respectively. Median MET SUV(max) for tumor and background were 2.2 and 1, respectively. There was a significant difference between MET tumor SUV(max) and MET background SUV(max) (P = .0001). The difference between FDG tumor SUV(max) and FDG background SUV(max) was not significant (P = .3672).
CONCLUSION: (11)C MET PET uptake is significantly greater within the tumor compared with noninvolved background white matter, making it more useful than FDG PET in identifying active tumor in patients with craniopharyngioma. Future work will focus on using (11)C MET PET to discriminate between active and inactive tumor after irradiation.