¹⁸F-fluoro-ethyl-tyrosine positron emission tomography for grading and estimation of prognosis in patients with intracranial gliomas

Introduction Histopathological examination is the standard for grading and determination of diagnosis in intrinsic brain tumors though the possibility of malignization and tumor heterogeneity always bears the possibility of tumor under-grading or misjudgement regarding the estimation of prognosis. The aim of the present study was to evaluate the use of ¹⁸F-FET-PET (FET-PET) for the grading and estimation of prognosis in newly diagnosed patients with intracranial gliomas in a clinical setting. Methods Patients who were treated for a newly diagnosed intracranial glioma between January 2007 and May 2012, and had a preoperative FET-PET and MRI scan between were included. The ratio of counts in a tumor VOI (volume of interest) with maximum uptake to the respective counts in a background VOI was calculated to provide the tumor-to-normal (T/N) ratio. The clinical and histopathological data (tumor grading, pre- and postoperative neurological status, Karnofsky Performance Status Scale scores, and overall survival rates) were recorded. Results One hundred fifty-two patients (39 WHO II, 26 WHO III, 87 WHO IV) were included. The median T/N ratio was 2.81 (1.1-8.1). The median T/N ratio of low-grade glioma patients was 1.65 (1.1-3.7), and 3.14 (1.61-8.1, p < 0.001) in high-grade glioma patients. The median survival for patients with WHO III tumors was 22.8 months (95% CI: 15.87%-NA) and 13.23 months (95% CI: 10.83-15.6.%) for patients with WHO IV tumors (p = 0.0001). For T/N ≤ 1.6, no deaths were recorded; for 1.6 < T/N ≤ 3, median survival was 25.6 months (95% CI: 16.5%-NA), while for T/N > 3, median survival was 14.0 months (95% CI: 11.7-16.2%, p < 0.001). The test of the maximally selected log-rank statistic resulted in a T/N ratio of 1.88 as the cut-off value, with the greatest difference in overall survival between patients with longer and shorter survival. The ROC curve for differentiation of low- vs. high-grade tumors with regard to the T/N ratio showed an area under the curve (AUC) of 0.903. Regarding the prognostic validity for overall survival ROC-curves for 12-month, 24-month and 48-month survival display a higher validity for the WHO-classification than for the imaging modalities though with an AUC of 0.847 for the 48-month survival T/N ratio and MRI contrast-enhancement have a high prognostic value as well. Conclusion Our study suggests that FET-PET can predict prognosis and survival in patients harboring intracranial gliomas and serves as a valuable tool to supplement the established clinical and histopathological parameters.