Study of 18 F-fluciclovine PET for serial assessment of glioblastoma tumor volumes during surgery and radiotherapy

Purpose: Recent evidence supports incorporating 18 F-Fluciclovine PET for glioblastoma treatment planning and monitoring, as it better captures tumor infiltration compared to conventional MRI. However, the relationship between PET- and MRI-defined tumor volumes remains unclear, particularly in the post-treatment setting. This study prospectively compares tumor volumes on MRI and PET at multiple timepoints throughout the treatment course and evaluates volumetric changes with therapy. Methods: We prospectively enrolled 8 adults with IDH-wildtype glioblastoma treated with surgery and chemoradiation between September 2019 and 2021. Participants underwent paired 18 F-Fluciclovine PET/CT and conventional MRI at four timepoints: preoperatively, pre-radiation, and at one- and six-months post-radiation. Biological tumor volume (BTV) from PET, FLAIR, and post-contrast T1volumes (T1CV) were segmented. Volumetric changes were compared using the Friedman test. Results: Participants (5 males, median age 63 years [IQR 54,66]) showed significantly larger BTVs compared to T1CV at diagnosis (median BTV = 27.2mL vs. T1CV = 13.3mL, adjusted P =.03), pre-radiation (BTV = 25.2mL vs. T1CV = 6.9mL, adjusted P =.03), and at one-month post-radiation (BTV = 27.3mL vs. T1CV = 12.1mL, P =.04). BTVs closely approximated yet were slightly smaller than their corresponding FLAIR volumes at all timepoints. After surgery, the median decrease in BTV (-4.4%) was significantly smaller than T1CV (-66.5%, P =.046), with a similar nonsignificant trend observed post-radiation (P =.50). Conclusion: Glioblastoma BTVs consistently exceed post-contrast T1 volumes and closely approximate FLAIR abnormalities throughout treatment. BTVs decline more gradually post-treatment, indicating persistent hypermetabolic tumor burden. Thus, 18 F-Fluciclovine PET can serve as an adjunct to conventional MRI in glioblastoma treatment planning and monitoring.