NEIM-02 CHARACTERIZATION OF LARGE BRAIN METASTASES WITH(18)F-FLUCICLOVINE PET/CT TREATED WITH STAGED STEREOTACTIC RADIOSURGERY (SSRS): INTERIM ANALYSIS OF A PILOT STUDY

We report the interim analysis of a phase 1, proof-of-concept study (NCT04689048), to assess the potential clinical utility of an amino acid radiotracer, (18)F-fluciclovine PET/CT, as a functional integral biomarker for previously untreated patients with large brain metastases [BM] (≥1 lesion; >2cm) treated with staged stereotactic radiosurgery (SSRS). We reviewed the imaging characteristics from static PET images acquired 10-25 minutes after (18)F-fluciclovine injection for the first seven enrolled patients (9 lesions) who completed baseline imaging, and five patients (7 lesions) who completed the treatment course (SSRS). Patients underwent a baseline (pre-treatment) (18)F-fluciclovine PET/CT and contrast-enhanced treatment planning brain MRI before 1(st) SSRS (15 Gy), repeated after 4 weeks (interim; before 2(nd) SSRS [15 Gy]), and 8 weeks after treatment completion (first follow-up after 2(nd) SSRS). The median age was 72 years and 57% were female. All lesions exhibited baseline increased (18)F-fluciclovine uptake compared to normal contralateral brain. The median baseline lesion diameters and volumes were 2.16 cm (1.76-3.22 cm) and 4.71cc (2.24-10.21 cc). The median baseline SUVmax, SUVpeak, and SUVmean values were 5.78 (2.16-8.79), 3.33 (0.5-2.72), and 1.75 (1.22-5.16), respectively. The median relative changes in diameter and volume were both -2% (-23% to +13% and -60% to +30%, respectively) at the interim scans, and -30% (-44% to +0.2%) and -43% (-94% to +13%), respectively, at first follow-up. Corresponding median relative changes values for SUVmax, SUVpeak, and SUVmean at interim scan were -20% (-73% to +174%), -9% (-75% to +99%), and -14% (-69% to +36%), and at first follow-up -59% (-87% to -21%), -41% (-86% to +11%), and -21% (-79% to +44%), respectively. In conclusion, this proof-of-concept interim study reports (18)F-fluciclovine metrics for patients with large BMs, demonstrating interval reduction in PET metrics after SSRS, more than anatomical measurements alone, highlighting the potential of this as an imaging biomarker.