[11C]-methionine positron emission tomography in the evaluation of pediatric low-grade gliomas

Background: [¹¹C]-Methionine positron emission tomography (PET; [¹¹C]-MET-PET) is principally used for the evaluation of brain tumors in adults. Although amino acid PET tracers are more commonly used in the evaluation of pediatric brain tumors, data on [¹¹C]-MET-PET imaging of pediatric low-grade gliomas (pLGG) is scarce. This study aimed to investigate the roles of [¹¹C]-MET-PET in the evaluation of pLGGs.

Methods: Eighteen patients with newly diagnosed pLGG and 26 previously treated pLGG patients underwent [¹¹C]-MET-PET met the inclusion and exclusion criteria. Tumor-to-brain uptake ratio (TBR) and metabolic tumor volumes were assessed for diagnostic performances (newly diagnosed, 15; previously treated 26), change with therapy (newly diagnosed, 9; previously treated 7), and variability among different histology (n = 12) and molecular markers (n = 7) of pLGGs.

Results: The sensitivity of [¹¹C]-MET-PET for diagnosing pLGG, newly diagnosed, and previously treated combined was 93% for both TBR_max and TBR_peak, 76% for TBR_mean, and 95% for qualitative evaluation. TBR_max showed a statistically significant reduction after treatment, while other PET parameters showed a tendency to decrease. Median TBR_max, TBR_peak, and TBR_mean values were slightly higher in the BRAFV600E mutated tumors compared to the BRAF fused tumors. Median TBR_max, and TBR_peak in diffuse astrocytomas were higher compared to pilocytic astrocytomas, but median TBR_mean, was slightly higher in pilocytic astrocytomas. However, formal statistical analysis was not done due to the small sample size.

Conclusions: Our study shows that [¹¹C]-MET-PET reliably characterizes new and previously treated pLGGs. Our study also shows that quantitative parameters tend to decrease with treatment, and differences may exist between various pLGG types.