Brain tumour imaging with PET:: a comparison between [18F]fluorodopa and [11C]methionine

Imaging of amino acid transport in brain tumours is more sensitive than fluorine-18 2-fluoro-deoxyglucose positron emission tomography (PET). The most frequently used tracer in this field is carbon-11 methionine (MET), which is unavailable for PET centres without a cyclotron because of its short half-life. The purpose of this study was to evaluate the performance of 3,4-dihydroxy-6-[F-18]fluoro-phenylalanine (FDOPA) in this setting, in comparison with MET. Twenty patients with known supratentorial brain lesions were referred for PET scans with FDOPA and MET. The diagnoses were 18 primary brain tumours, one metastasis and one non-neoplastic cerebral lesion. All 20 patients underwent PET with FDOPA (100 MBq, 20 min p.i.), and 19 of them also had PET scans with MET (800 MBq, 20 min p.i.). In all but one patient a histological diagnosis was available. In 15 subjects, histology was known from previous surgical interventions; in five of these patients, as well as in four previously untreated patients, histology was obtained after PET. In one untreated patient, confirmation of PET was possible solely by correlation with MRI; a histological diagnosis became available 10 months later. MET and FDOPA images matched in all patients and showed all lesions as hot spots with higher uptake than in the contralateral brain. Standardised uptake value ratios, tumour/contralateral side (mean+/-SD), were 2.05+/-0.91 for MET and 2.04+/-0.53 for FDOPA (NS). The benign lesion, which biopsy revealed to be a focal demyelination, was false positive, showing increased uptake of MET and FDOPA. We conclude that FDOPA is accurate as a surrogate for MET in imaging amino acid transport in malignant cerebral lesions for the purpose of visualisation of vital tumour tissue. It combines the good physical properties of F-18 with the pharmacological properties of MET and might therefore be a valuable PET radiopharmaceutical in brain tumour imaging.