Aim: To evaluate the prognostic value of O-(2-[(18)F]fluoroethyl)-L-tyrosine positron emission tomography (FET-PET) uptake intensity in World Health Organisation (WHO) tumor grade II-IV gliomas.
Methods: We studied 28 patients with WHO tumor grade II-IV gliomas who were referred to our department for radiation therapy. We acquired a FET-PET in all patients, as well as magnetic resonance imaging (MRI) of the brain consisting of at least T2-weighted imaging, flair and pre- and post-contrast T1-weighted imaging. SUVmax was measured and the tumor-to-brain uptake ratio (TBR) of all lesions was calculated based on the SUVmax (TBRmax) or SUVmean (TBRmean) of the contralateral healthy tissue. For this study, volumes were calculated using MRI alone, MRI + the volume with a SUVmax on FET-PET ≥ 2.2 as well as MRI + the volume with an uptake of at least 40 % of the SUVmax.
Results: Tumor volumes were a median (range) of 88.6 (2.6-467.4) ml (MRI alone), 84.2 (2.8-474.4) ml (MRI + SUVmax on FET-PET ≥ 2.2) and 101.5 (4.0-512.1) ml (MRI + FET-PET uptake ≥ 40 % SUVmax), respectively. TBR-SUVmean was 2.36 (1.46-4.08); TBR-SUVmax was 1.71 (0.97-2.85). During a follow-up of 18.7 (2.5-36.1) months after FET-PET, 12 patients died of malignant glioma. Patients with a SUVmax ≥ 2.6 had a significantly worse tumor-related mortality (p = 0.005) and progression-free survival (p = 0.038) than those with a lower SUVmax. Multivariate analysis showed that WHO tumor grade (p = 0.001) and SUVmax ≥ 2.6 (p < 0.001) were independent predictors for tumor-related mortality, but not tumor volume or TBRmax or TBRmean. SUVmax ≥ 2.6 (p = 0.007) and being treated for a recurrence rather than for a primary tumor manifestation (p = 0.014) were predictors for progression-free survival, but not TBRmax or TBRmean.
Conclusion: In this heterogeneous patient population, higher tracer uptake in FET-PET appears to be associated with a worse tumor-related mortality and a shorter duration of the disease-free interval.