Brain Tumors: Diagnostic Impact of PET Using Radiolabelled Amino Acids

Abstract

Magnetic resonance tomography (MRT) allows an exact morphologic visualisation of the brain and is the investigation of choice for diagnosing cerebral glioma, but its capacity to differentiate tumor tissue from non-specific tissue changes is limited. Positron emission tomography (PET) using radiolabeled amino acids provides additional metabolic information which helps increase diagnostic accuracy. The use of radiolabeled amino acids allows better delineation of tumor margins and improves targeting of biopsy and radiotherapy, and planning surgery. In addition, amino acid imaging appears useful in distinguishing tumor recurrence from non-specific post-therapeutic edema and scar tissue, in predicting prognosis in low grade gliomas, and in monitoring metabolic response during treatment. Most PET studies of cerebral gliomas have been performed with the amino acid ¹¹C-methyl-L-methionine (MET), although the short half-life of ¹¹C (20 min) limits the use of this technique to the few centers that are equipped with an in-house cyclotron facility. In recent years ¹⁸F-labelled amino acids (half-life 109 min) such as O-(2-[¹⁸F]fluoroethyl)-L-tyrosine (FET) have been developed that allow a more widespread use of amino acid imaging. The logistical prerequisites for amino acid imaging of brain tumors have become markedly less difficult with the introduction of ¹⁸F-labelled amino acids like FET. The scientifically documented utility of amino acid imaging of cerebral gliomas justifies its use as a routine diagnostic technique for certain indications.