NIMG-53. REPEATABILITY OF O-(2-18F-FLUOROETHYL)-L-TYROSINE POSITRON EMISSION TOMOGRAPHY (FET-PET) SCANNING AND THE INFLUENCE OF PROTEIN INTAKE IN GLIOMA

BACKGROUND: FET-PET scanning is used in routine clinical management and evaluation of glioma brain tumours. Clinical guidelines recommend fasting 4–6 hours before a FET-PET scan. Animal studies indicate that protein intake prior to the scan does not reduce FET-uptake in tumours, but there are no human studies published. Critical knowledge of test-retest variation of FET-PET imaging of glioma tumour volume as well as uptake and the impact of protein intake is sparse. AIM: This study investigated the repeatability of FET-PET scanning and the impact of protein-intake prior to FET-PET scanning of gliomas. MATERIALS AND METHODS: 20 histologically confirmed glioma patients were included in this prospective study. Subjects were divided into two groups; no protein (NP, n=11) and protein (P, n=9). All subjects underwent two 40 min. dynamic FET-PET scans on a Siemens PET/CT scanner with an interval of maximum 7 days between each scan. Group P consumed 24g of protein (Nutricia Nutridrink Compact®) orally an hour before the second scan. Blood samples were drawn before and after protein intake for determining the plasma-amino-acid concentration. None of the patients were in treatment at the time of the scans. Volumes of interest were delineated on the 20–40 min 18F-FET PET acquisition co-registered to contrast enhanced T1-weighted MRI. The two scans were compared by calculating the absolute change between healthy appearing cortex (B), the maximal and the mean tumour uptake normalized to B (Tmax/B; Tmean/B) and by measuring the biological tumour volume (BTV) defined as uptake above 1.6 mL of mean in healthy appearing brain. RESULTS: The absolute change in FET tumour metrics, mean (range) Tmax/B: NP=0.12[-0.11;0.52] P=0.16[-0.11;0.82] Tmean/B: NP=0.20[-0.06; 2.00] P=0.06[-0.03;0.22] BTV(mL): NP=0.76[-1.50;3.30] P=2.59[-0.02; 12.0] All results were non-significant, p-value > 0.05 CONCLUSION: Tumour day-to-day variation might be greater than first anticipated. Updated results will be presented.