Introduction: National Comprehensive Cancer Network HCC guidelines recommend Y90 to treat BCLC-C patients only in select cases given the development of systemic regimens. We sought to identify ideal candidates for Y90 by assessing survival and toxicities in this patient group.Materials and Methods: The Radiation-Emitting Selective Internal radiation spheres in Non-resectable tumor registry is a prospective observational study (NCT: 02,685,631). Patients with advanced HCC were stratified into 3 groups based on tumor location, Eastern Cooperative Oncology Group (ECOG) performance status, and liver function. Group 1: liver isolated HCC, ECOG 0 and Child Pugh (CP) A (n = 12, 16%), Group 2: liver isolated HCC, ECOG ≥ 1 or CP B/C (n = 37, 49%), and Group 3: extrahepatic HCC with any ECOG or CP score (n = 26, 35%). Patients in any group could have macrovascular invasion. Overall survival (OS) and progression-free survival (PFS) with 95% confidence intervals (95% CI) were calculated. Grade 3 + toxicities were tracked using Common Terminology Criteria for Adverse Events v5. Cox proportional hazard model was performed to determine factors affecting OS.Results: Seventy-five BCLC-C patients treated between 2015 and 2019 were reviewed. The groups were similar in age, sex, race, and ethnicity (all p > 0.05). Bilobar disease was least common in Group 1 (p < 0.001). Median OS of the entire cohort was 13.6 (95% CI 7.5-16.1) months. Median OS of Groups 1-3 were 21.8, 13.1 and 11.5 months respectively (p = 0.6). Median PFS for the cohort was 6.3 (4.8-14.7) months. Median PFS for group 1 was not reached. Mean PFS for Group 1 was 17.3 ± 4.8 months. Median PFS for Groups 2 and 3 was 6.8 and 5.9 months (X2 = 1.5, p = 0.5). Twenty-four Grade 3 or greater toxicities developed, most commonly hyperbilirubinemia (8/75, 11%) and thrombocytopenia (2/75, 3%). The incidence of toxicities between groups was similar (all p > 0.05). Cox Proportional Hazard analysis predicted shorter OS with CP class B/C (X2 = 6.7, p = 0.01), while macrovascular invasion (X2 = 0.5, p = 0.5) and ECOG score of ≥ 1 (X2 = 2.1, p = 0.3) was not associated with OS.Conclusions: OS of CPA patients with advanced HCC and performance status of 0 was 21.8 months following Y90. CP A cirrhosis is the best predictor of prolonged OS in advanced (BCLC-C) HCC. [ABSTRACT FROM AUTHOR]