FET PET for the evaluation of untreated gliomas:: correlation of FET uptake and uptake kinetics with tumour grading

Purpose Treatment and prognosis of gliomas depend on their histological tumour grade. The aim of the study was to evaluate the potential of [F-18]fluoroethyltyrosine (FET) PET for non-invasive tumour grading in untreated patients. Methods Dynamic FET PET studies were performed in 54 patients who, based on MRI, were estimated to have low grade (LG; n = 20), intermediate (WHO II-III; n = 4) or high grade (HG; n = 30) tumours. For standard evaluation, tumour SUVmax and the ratio to background (SUVmax/BG) were calculated (sum image: 20-40 min). For dynamic evaluation, mean SUV values within a 90% isocontour ROI (SUV90) and the SUV90/BG ratios were determined for each time frame to evaluate the course of FET uptake. Results were correlated with histopathological findings from PET-guided stereotactic biopsies. Results Histology revealed gliomas in all patients. Using the standard method a statistically significant difference (p = 0.001) was found between LG (n = 20; SUVmax/BG: 2.16 +/- 0.98) and HG (n = 34; SUVmax/BG: 3.29 +/- 1.06) gliomas (opt. threshold 2.58: SN71%/SP85%/area under ROC curve [AUC]:0.798), however, with a marked overlap between WHO II to IV tumours. Time activity curves showed slight increase in LG, whereas HG tumours presented with an early peak (10-20 min) followed by a decrease. Dynamic evaluation successfully separated LG from HG gliomas with higher diagnostic accuracy (SN94%/SP100%/AUC:0.967). Conclusions Based on the ratio-based method, a statistically significant difference was found between LG and HG gliomas. Due to the interindividual variability, however, no reliable individual grading was possible. In contrast, dynamic evaluation allowed LG and HG gliomas to be differentiated with high diagnostic power and, thus, should supplement the conventional method.