P09.12.B INFLUENCE OF PATIENT CHARACTERISTICS AND ADJUVANT TEMOZOLOMIDE CHEMOTHERAPY ON FET UPTAKE IN THE REFERENCE REGION IN PATIENTS WITH GLIOMAS

Abstract BACKGROUND In PET imaging, the uptake of radiolabeled amino acids in the reference region is frequently used to calculate tumor-to-brain ratios in patients with gliomas. Nevertheless, besides patient characteristics, our understanding of the alkylating chemotherapy’s influence on the uptake of radiolabeled amino acid in the reference region in patients with CNS WHO grade 3 or 4 gliomas is incomplete. MATERIAL AND METHODS We evaluated the effects of sex, age, and adjuvant chemotherapy with temozolomide on the uptake of O-(2-[18F]fluoroethyl)-L-tyrosine (FET) in the reference region in newly diagnosed glioma patients who had undergone surgery and radiotherapy with concomitant temozolomide chemotherapy. FET PET was performed at baseline and after the second cycle of adjuvant temozolomide chemotherapy. Besides, we calculated standardized uptake values (SUV) of FET in the reference region located in the contralateral, unaffected hemisphere. Unpaired Student’s t-tests were used to test differences between independent groups (e.g., females and males). The paired Student’s t-test was used to compare background SUV at baseline and follow-up. The Pearson’s correlation coefficient determined correlations between clinical parameters and SUV in the background region. RESULTS Sixty-three patients with gliomas (females, n=32) were retrospectively evaluated (CNS WHO grade 4 glioblastoma, n=55; CNS WHO grade 4 H3K27-mutant diffuse midline glioma, n=2; CNS WHO grade 4 astrocytoma, n=4; CNS WHO grade 3 astrocytoma, n=1; CNS WHO grade 3 oligodendroglioma, n=1). SUV in the reference region did not significantly differ between female and male patients at baseline (P=0.259) and follow-up (P=0.384). Patients’ age at initial diagnosis was positively correlated with background SUV at baseline (r=0.384; P=0.002). After two cycles of adjuvant temozolomide chemotherapy, the SUV in the reference region at follow-up was not significantly different from baseline (P=0.485). CONCLUSION Our data suggest that the reference SUV was unaffected by adjuvant temozolomide chemotherapy. In contrast, age has a modest influence on the physiological FET uptake. Further studies to evaluate the impact of patient characteristics and treatment are warranted.