Uptake of [N-methyl-11C]α-methylaminoisobutyric acid in untreated head and neck cancer studied by PET

Amino acid transport system A is expressed strongly in neoplastic cells. [N-methyl-11C]α-Methylaminoisobutyric acid (11C-MeAIB) is a recently developed tracer for PET studies on system A amino acid transport. 11C-MeAIB is a metabolically stable amino acid analogue which is transported from plasma into the tissue by system A. This study evaluated the kinetics of 11C-MeAIB uptake from plasma into tumour tissue and normal tissues in 13 patients with untreated head and neck cancer. 11C-MeAIB uptake in tumour was compared with histological grade and proliferative activity. Tracer uptake was quantitated by calculating the standardised uptake values (SUVs) and the kinetic influx constants (Ki) using graphical analysis. All tumours accumulated 11C-MeAIB and were visualised clearly. In the graphical analysis, linear plots were achieved; the mean Ki value of tumour was 0.056±0.026 min-1, and the mean SUV was 6.1±2.7. A close correlation between graphically obtained Ki and semi-quantitative SUV in tumours was found (r=0.887, P=0.00005). We could not demonstrate a correlation between the uptake of 11C-MeAIB and the grade of malignancy or the proliferative index, as assessed using Ki-67 immunohistochemical assay. Head and neck cancer can be effectively imaged with 11C-MeAIB PET. 11C-MeAIB showed active and rapid transport into tumour tissue and salivary glands. Further studies on the applicability of 11C-MeAIB PET for radiation treatment planning in the head and neck region and the regulation of system A amino acid transport under different metabolic states are warranted. (orig.)