IMG-94. Assessment of rhenium-186 obisbemeda (186RNL) therapy for recurrent glioblastoma (rGBM) using MRI and SPECT imaging biomarkers

Abstract BACKGROUND The treatment of recurrent glioblastoma remains a significant challenge in modern neuro-oncology. Targeted radiotherapy offers the potential to improve local tumor control while reducing toxicity to surrounding healthy brain tissue. In our ongoing Phase 2 clinical trial, administration of rhenium-186 nanoliposome (186RNL) at doses exceeding 100Gy has demonstrated promising improvements in overall survival (OS) among patients with rGBM. This study aims to evaluate the efficacy of 186RNL therapy using imaging biomarkers derived from MRI and SPECT. METHODS Twenty-six patients with rGBM were enrolled. Longitudinal MRI and SPECT imaging were performed to assess 186RNL delivery and response. The tumor volume was determined using the difference (delta T1 weighted images) between pre- and post-contrast T1 weighted MRI images, while 100Gy dose treated tumor volume determined based on SPECT images and Tumor ROIs. Treatment coverage ratio (TCR), standardized relative cerebral blood volume (srCBV), Time to maximum (Tmax), time to peak (TTP), mean transit time (MTT), and other imaging biomarkers were calculated. RESULTS The administered 186RNL dose showed a strong positive correlation with TCR (r = 0.722, p > 0.001), and significant negative correlations with MTT (r = -0.499, p = 0.008) and tumor volume (r = -0.379, p = 0.0226), indicating more efficient treatment delivery in smaller, well perfused tumors. TTP was positively correlated with progression free survival (PFS) (r = 0.504, p = 0.0166), while OS was negatively associated with tumor volume (r = -0.392, p = 0.0293) and MTT (r = -0.429, p = 0.0464). CONCLUSION These findings support the effectiveness of combining MRI and SPECT imaging to access 186RNL delivery and its therapeutic outcomes in rGBM. Imaging biomarkers such as TCR, MTT and TTP may serve as useful predictors of treatment response and clinical outcomes and could guide future patient-specific treatment planning.