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

Abstract

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-[(18)F]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 (18)F with the pharmacological properties of MET and might therefore be a valuable PET radiopharmaceutical in brain tumour imaging.

PET for Therapy Response Assessment in Glioblastoma

“…Most PET studies of cerebral gliomas have been performed with 11 C-MET, although the short half-life of 11 C (20 min) limits the use of this tracer to the few centers that are equipped with an on-site cyclotron facility. Results with 18 F-FET PET are similar to those with 11 C-MET (63), and due to its longer half-life (109 min) and lack of (or minimal) uptake in macrophages and inflammatory cells, 18 F-FET PET is preferred for clinical use (56,59,61,(64)(65)(66)(67). The diagnostic potential of 18 F-FET PET in brain tumors is well documented, for example, a superior delineation of human gliomas by 18 F-FET PET compared with MRI and a high specificity for the detection of gliomas and biopsy site planning (31,64,68).…”

“…Labeled amino acid tracers developed so far for PET imaging are divided into two categories: tracers actively incorporated into the proteins, such as 11 C-Methionine ( 11 C-MET), potentially allowing investigating protein synthesis, and tracers not integrated into proteins, such as 18 F-fluoroethyltyrosine ( 18 F-FET) and 3,4-dihydroxy-6-18 F-fluoro-l-phenylalanine ( 18 F-FDOPA), which are valuable tools to evaluate amino acid transport (59). The increased uptake of 18 F-FET and 18 F-FDOPA by cerebral glioma tissue appears to be caused mainly by increased transport via sodium-independent amino acid transport system L for large neutral amino acids (LATs) and Na + -dependent general amino acid transporters B 0,+ and B 0 , with a disruption of the BBB not being a prerequisite for intratumoral accumulation (20,(60)(61)(62). Most PET studies of cerebral gliomas have been performed with 11 C-MET, although the short half-life of 11 C (20 min) limits the use of this tracer to the few centers that are equipped with an on-site cyclotron facility.…”

PET/CT imaging in cancer: Current applications and future directions

“…113 FDOPA-PET also was compared with MET-PET in patients with primary brain tumors or brain metastases and, similarly, yielded comparable diagnostic information. 114 FACBC has been studied primarily in prostate cancer, in which it had higher sensitivity for tumor detection compared with 111 In-capromab pendetide (Prostascint) and 11 C-choline. 115,116 In addition, FACBC has demonstrated increased uptake in papillary renal cell carcinoma, but not in clear cell carcinoma.…”

Current Molecular Imaging Positron Emitting Radiotracers in Oncology

“…MET-PET has been used in clinical management of cerebral gliomas in initial diagnosis, differentiation of tumor recurrence, grading, prognostication, tumor extent delineation, biopsy planning, surgical resection, radiotherapy planning, and assessment of response to therapy [12]. MET-PET is also used clinically to distinguish malignant tissue from normal tissue or benign growths in head and neck cancer, melanoma, ovarian cancer, and other tumors [13][14][15][16], but the short physical half-life of C-11 prevents its use in most nuclear medicine departments (i.e., those without an on-site cyclotron).…”

“…It is critical for the growth of primary malignant tumors and for the development of metastases. A number of radiotracers are available to characterize tissue vascularity, e.g., 15 O-labeled water and carbon monoxide, which can quantify tissue perfusion and blood volume, respectively [59]. PET angiogenesis imaging could provide medical information at the functional and molecular levels.…”