Quantitative evaluation of neutral amino acid transport in cerebral gliomas using positron emission tomography and fluorine-18 fluorophenylalanine

To elucidate the mechanism of large neutral amino acid (LNAA) transport in cerebral gliomas and to evaluate the clinical usefulness of positron emission tomography (PET) with fluorine-18 fluorophenylalanine (¹⁸F-Phe), we examined 18 patients with cerebral glioma using dynamic PET and¹⁸F-Phe. By employing two-compartment model analysis, the influx rateK₁, the efflux ratek₂ and the distribution volume (V_d) of¹⁸F-Phe were estimated in tumour tissue and contralateral normal grey matter.¹⁸F-Phe showed increased accumulation in tumour tissue regardless of the grade of malignancy in all patients. The rate of uptake of¹⁸F-Phe in high-grade glioma was significantly higher than in low-grade glioma (P <0.05). However, it was difficult to evaluate the tumour grade only from the¹⁸F-Phe accumulation in individual cases. Values ofK₁ andV_d were significantly increased in the tumour tissue. TheK₁ value of the tumour tissue tended to decrease with increasing LNAA concentration in plasma. Therefore, influx of¹⁸F-Phe into tumour tissue is mainly related to the carrier-mediated active transport. It is concluded that PET with¹⁸F-Phe is of clinical value for tumour detection rather than assessment of tumour malignancy.