The most common type of
primary brain tumor is
malignant glioma. Despite intensive therapeutic efforts, the majority of these
neoplasms remain incurable. Imaging techniques are important for initial
tumor detection and comprise indispensable tools for monitoring treatment. Structural imaging using contrast-enhanced MRI is the method of choice for
brain tumor surveillance, but its capacity to differentiate
tumor from nonspecific tissue changes can be limited, particularly with posttreatment
gliomas. Metabolic imaging using positron-emission-tomography (PET) can provide relevant additional information, which may allow for better assessment of
tumor burden in ambiguous cases. Specific PET tracers have addressed numerous molecular targets in the last decades, but only a few have achieved relevance in routine clinical practice. At present, PET studies using radiolabeled
amino acids appear to improve clinical decision-making as these tracers can offer better delineation of
tumor extent as well as improved targeting of biopsies, surgical interventions, and
radiation therapy.
Amino acid PET imaging also appears useful for distinguishing
glioma recurrence or progression from postradiation treatment effects, particularly radiation
necrosis and pseudoprogression, and provides information on histological grading and patient prognosis. In the last decade, the tracers O-(2-[(18)F]fluoroethyl)-
L-tyrosine (FET) and 3,4-dihydroxy-6-[(18)F]-fluoro-
L-phenylalanine (FDOPA) have been increasingly used for these indications. This review article focuses on these tracers and summarizes their recent applications for patients with
brain tumors. Current uses of tracers other than FET and FDOPA are also discussed, and the most frequent practical questions regarding PET
brain tumor imaging are reviewed.