Evaluation of 18F-FDG PET and MRI Associations in Pediatric Diffuse Intrinsic Brain Stem Glioma: A Report from the Pediatric Brain Tumor Consortium

The purpose of this study was to assess 18F-FDG uptake in children with a newly diagnosed diffuse intrinsic brain stem glioma (BSG) and to investigate associations with progression-free survival (PFS), overall survival (OS), and MRI indices. Methods: Two Pediatric Brain Tumor Consortium (PBTC) therapeutic trials in children with newly diagnosed BSG were designed to test radiation therapy combined with molecularly targeted agents (PBTC-007: phase I/II study of gefitinib; PBTC-014: phase I/II study of tipifarnib). Baseline brain 18F-FDG PET scans were obtained in 40 children in these trials. Images were evaluated by consensus between 2 PET experts for intensity and uniformity of tracer uptake. Associations of 18F-FDG uptake intensity and uniformity with both PFS and OS, as well as associations with tumor MRI indices at baseline (tumor volume on fluid-attenuated inversion recovery, baseline intratumoral enhancement, diffusion and perfusion values), were evaluated. Results: In most of the children, BSG 18F-FDG uptake was less than gray-matter uptake. Survival was poor, irrespective of intensity of 18F-FDG uptake, with no association between intensity of 18F-FDG uptake and PFS or OS. However, hyperintense 18F-FDG uptake in the tumor, compared with gray matter, suggested poorer survival rates. Patients with 18F-FDG uptake in 50% or more of the tumor had shorter PFS and OS than did patients with 18F-FDG uptake in less than 50% of the tumor. There was some evidence that tumors with higher 18F-FDG uptake were more likely to show enhancement, and when the diffusion ratio was lower, the uniformity of 18F-FDG uptake appeared higher. Conclusion: Children with BSG for which 18F-FDG uptake involves at least half the tumor appear to have poorer survival than children with uptake in less than 50% of the tumor. A larger independent study is needed to verify this hypothesis. Intense tracer uptake in the tumors, compared with gray matter, suggests decreased survival. Higher 18F-FDG uptake within the tumor was associated with enhancement on MR images. Increased tumor cellularity as reflected by restricted MRI diffusion may be associated with increased 18F-FDG uniformity throughout the tumor.