Prognostic Value of Metabolic Tumor Volume on 11C-Methionine PET in Predicting Progression-Free Survival in High-Grade Glioma

Purpose C-11 methionine (MET) PET is commonly used for diagnosing high-grade glioma (HGG). Recently, volumetric analysis has been widely applied to oncologic PET imaging. In this study, we investigated the prognostic value of metabolic tumor volume (MTV) on MET PET in HGG. Methods A total of 30 patients with anaplastic astrocytoma (n= 12) and glioblastoma multiforme (n= 18) who underwent MET PET before treatment (surgery followed by chemoradiotherapy) were retrospectively enrolled. Maximal tumor-to-normal brain ratio (TNRmax, maximum tumor activity divided by mean of normal tissue) and MTV (volume of tumor tissue that shows uptake>1.3-fold of mean uptake in normal tissue) were measured on MET PET. Adult patients were classified into two subgroups according to Radiation Therapy Oncology Group Recursive Partitioning Analysis (RTOG RPA) classification. Prognostic values of TNRmax, MTV and clinicopathologic factors were evaluated with regard to progression-free survival (PFS). Results Median PFS of all patients was 7.9 months (range 1.0-53.8 months). In univariate analysis, MTV (cutoff 35 cm(3)) was a significant prognostic factor for PFS (P=0.01), whereas TNRmax (cutoff 3.3) and RTOG RPA class were not (P=0.80 and 0.61, respectively). Treatment of surgical resection exhibited a borderline significance (P=0.06). In multivariate analysis, MTV was the only independent prognostic factor for PFS (P=0.03). Conclusion MTV on MET PET is a significant and independent prognostic factor for PFS in HGG patients, whereas TNRmax is not. Thus, performing volumetric analysis of MET PET is recommended in HGG for better prognostication.