Physiological Biodistribution of 18F-fluciclovine in The Head

Objective: Anti-1-amino-3-[18F]fluorocyclobutane-1-carboxylic acid (18F-fluciclovine; anti-3-[18F]FACBC) is an amino acid positron emission tomography (PET) tracer used for the evaluation of brain tumors in cases of suspected or diagnosed glioma. However, reports on the physiological biodistribution of 18F-fluciclovine in the head, are limited. This study retrospectively analyzed the physiological biodistribution of 18F-fluciclovine PET in the head. Methods: We analyzed 18F-fluciclovine PET/CT images of 20 patients who were suspected of malignant glioma. The maximum and mean standard uptake values (SUVmax and SUVmean) were measured in the 24 areas of the head tissues. Time-activity curves were generated, with the volume of index placed in the same manner as for the SUV measurements to obtain dynamic uptake over time. Differences in SUV between regions were assessed using one-way analysis of variance. Among 20 patients who received 18F-fluciclovine PET/CT, physiological biodistribution analyses were performed in 8 patients who also underwent 11C- methionine PET/CT. Comparisons of SUV between 18F-fluciclovine and 11C-methionine PET were performed using paired t-tests. Statistical significance was set at P < 0.05 for all analyses. Results: 18F-fluciclovine uptake in the cerebral cortex was uniformly low (mean SUVmean 0.3 ± 0.1), with slightly higher values in the basal ganglia, thalamus, midbrain, pons, medulla oblongata, cerebellum, and cerebellar vermis (0.4 ± 0.1). Among extracerebral regions, the highest uptake was in the parotid gland (3.4 ± 0.8), followed by the pharynx (2.5 ± 0.5), pituitary gland, nasal cavity (2.3 ± 0.4), muscle (2.2 ± 0.6), bone marrow (2.0 ± 0.5), and skin (1.9 ± 0.6). In 15 patients, brain uptake remained low and stable, while the pituitary gland and parotid glands peaked immediately after injection and declined rapidly. In 8 patients with 11C-methionine PET, methionine showed significantly higher uptake in all brain regions, whereas 18F-fluciclovine was higher in the venous sinus, cavernous sinus, muscle, and nasal cavity. Conclusion: Understanding these physiological biodistribution patterns of 18F-fluciclovine PET is essential for distinguishing between pathological uptake patterns and for providing useful baseline data. Furthermore, 18F-fluciclovine uptake in the brain was uniformly low in the cerebral cortex, with minimal nonspecific uptake, suggesting that it may contribute to defining tumor margins.