Statistical analysis
The primary outcome, progression event-free survival (EFS), was defined as the date from initiating therapy to recurrence or metastasis. In some included studies, disease-free survival (DFS) or progression-free survival (PFS) was obtained as the primary outcome, but they were all redefined as EFS in this meta-analysis. The secondary outcome was overall survival (OS), defined as the date from initiating therapy until death. The effect sizes of the prognostic values of SUVmax, SUVmean, MTV, and TLG were measured in terms of HR. An HR greater than 1 implied worse survival for patients with a high SUVmax, SUVmean, MTV, or TLG. The most adjusted estimate of hazard ratio (HR) was extracted directly from each study, if provided by the authors. Otherwise, the HR estimate and its variance were extracted from Kaplan-Meier curves by Engauge Digitizer, version 3.0 (http://digitizer.sourceforge.net). Heterogeneity was assessed with the Q test and I 2 statistic, andP value less than 0.05 or I 2 values higher than 50% indicated significant heterogeneity. The fixed-effects model was used to estimate the cases with homogeneity and the random-effects model was used for the cases with significant heterogeneity. Publication bias of the studies was visually displayed by the asymmetry of an inverted funnel plot, and quantitatively evaluated by Egger’s tests with the P value less than 0.05 suggesting the significant publication bias. Sensitivity analyses were conducted to assess the stability of the meta-analysis results. All statistical analysis was conducted with STATA 14.0 (STATA Corporation, College Station, TX, USA) software.