Comparative analysis of 5-ALA-induced fluorescence intensity and 11C-Methionine PET uptake in glioma surgery

Background: 5-aminolevulinic acid (5-ALA) induces red fluorescence in malignant brain tumors that has been used for intraoperative guidance for tumor removal. Positron emission tomography with 11C-Methionine (Met-PET) is a promising imaging modality to depict clear boundary of infiltrating glioma. We studied the correlation between preoperative Met-PET uptake and intraoperative 5-ALA fluorescence. Method: Patients who underwent preoperative Met-PET study and tumor removal using 5-ALA over a period of two years were analyzed. The regional uptake of Met-PET was expressed as the ratio of the maximum of standardized uptake value (SUV-max) to the contralateral normal brain. 5-ALA fluorescence from tumor sample was immediately measured during surgery using blue laser and spectrometer. Fluorescence intensity was categorized into four groups (None, Weak, Moderate, Strong) with ten-hold differences. Results: 16 cases with pathological diagnosis of astrocytic tumors were analyzed. Met-PET uptake was markedly high in “Strong” fluorescence group (3.81±0.77). Particularly, among 11 newly-diagnosed cases, the difference was statistically significant (p=0.017, Kruskal-Wallis test). "Strong" fluorescence group still showed significant difference when compared with other groups together, in all cases and newly-diagnosed cases (p=0.01 and p=0.004, respectively, Mann- Whitney U test). Discussion/Conclusion: There are limited number of reports regarding 5-ALA and Met-PET, stating that Met-PET and 5- ALA fluorescence should be considered separately. However, the fluorescence was grossly distinguished whether positive or negative. Our study utilized objective spectroscopic measurement of fluorescence intensity. The results suggested that strong fluorescence intensity induced by 5-ALA reflects high Met-PET uptake. This could indicate the importance of bright fluorescence by 5-ALA in glioma surgery.