Non-invasive grading of primary brain tumours: Results of a comparative study between SPET with I-123-alpha-methyl tyrosine and PET with F-18-deoxyglucose

Use of iodine-123-alpha-melhyl tyrosine (I-123-IMT) allows investigation of the amino acid transport rate in gliomas. It was the aim of this study to compare the value of measurement of glucose metabolism with that of measurement of I-123-IMT uptake for the non-invasive grading of brain tumours. The study population comprised 23 patients with histopathologically proven primary brain tumours, 14 had high-grade gliomas, and nine low-grade brain neoplasms, Glucose metabolism was studied using an ECAT EXACT 47 positron emission tomography (PET) camera and fluorine-18 fluorodeoxyglucose (F-18-FDG); I-123-IMT uptake was measured with the triple-headed single-photon emission tomography (SPET) camera, MULTISPECT 3. F-18-FDG and I-123-IMT uptake was quantified as ratios between the uptake by the tumour and contralateral regions of reference. Glucose metabolism and amino acid uptake of the brain tumours correlated significantly (r = 0.71, P < 0.001). Assuming discrimination thresholds between high-grade and low-grade tumours of 0.8 for F-18-FDG uptake and 1.8 for I-123-IMT uptake, the accuracy values of F-18-FDG PET and I-123-IMT SPET for differentiating between high-grade and low-grade rumours were 21/23 (91%) and 19/23 (83%), respectively. The difference in diagnostic performance was not significant on receiver operating characteristic analysis (P > 0.4). It is concluded that there is no major difference between the PET investigation of glucose metabolism and the less expensive SPET measurement of amino acid uptake in terms of their accuracy in evaluating the malignancy grade of primary brain tumours, This encourages the performance of further studies to analyse the potential impact of I-123-IMT SPET on the therapeutic management of patients with brain tumours.