A comparative study of pediatric CNS tumor activity as assessed by [18F]-FDG PET imaging and proton magnetic resonance spectroscopic imaging.

Abstract

2101 Background: Magnetic resonance spectroscopic imaging (MRSI) allows in vivo analysis of tumor metabolism in discrete areas of the tumor. Changes in the ratio of two metabolites, choline and N-acetyl aspartate, (Cho:NAA) have been associated with tumor grade, treatment response and outcome. Fluorine-18 fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) is the current standard of care to assess tumor metabolism, and FDG uptake has correlated with tumor grade and proliferative status. The relationship between tumor metabolic activity on MRSI and FDG-PET is unclear. The objective of this study was to compare the determination of metabolically active tissue between MRSI and FDG-PET in pediatric brain tumors. Methods: Children with a brain tumor or residual lesion after therapy underwent FDG-PET and a standard MRI with MRSI within a two-week period. FDG uptake and maximum Cho:NAA were each used to classify tumors as inactive, active, and highly active. The agreement between the two measures was determined using the percent agreement and the kappa statistic (K). Results: FDG-PET and MRSI were acquired in 37 patients (15M/22F) with a median age of 12.3 years. Tumor diagnoses included 20 brainstem gliomas, 8 high-grade, 8 low-grade gliomas and 1 patient with Lhermitte-Duclos disease. Four studies were excluded. Increased metabolic activity was identified in the majority of both PET and MRSI studies (Table), but overall agreement between MRSI and PET was weak (K=0.16), with only 14 of 33 studies yielding the same classification. The percent agreement between PET and MRSI was 42% (95% CI = 25 – 61%, p = 0.49). Patients continue to accrue to see if the results are applicable in a larger population. Conclusions: Pediatric brain tumors have a heterogeneous metabolic expression pattern on MRSI and FDG-PET. There was little agreement between maximum Cho:NAA values and maximum FDG-PET activity. MRSI classification PET classification Inactive (n=14) Active (n=9) Highly active (n=10) Inactive (n=8) 6 2 0 Active (n=23) 7 7 9 Highly active (n=2) 1 0 1