Yttrium-90 resin microsphere transarterial radioembolization in unresectable hepatocellular carcinoma: Early results with scout dose–based lung shunt estimation and dosimetry.

155 Background: Yttrium-90 TARE is an effective locoregional therapy for HCC. TARE traditionally requires 99mTc-MAA for lung shunt fraction (LSF) estimation. Our hospital lacked a functional gamma camera, which made 99mTc-MAA imaging impossible. We aimed to report our initial results using scout Y-90 for LSF estimation, dosimetry planning and interim treatment response. Methods: Between May 2025 and January 2026, forty four consecutive patients were evaluated for Y-90 TARE. After injection of the Y-90 scout dose, PET/CT images were acquired, and LSF and lung dose (LD) calculations were performed using MIM-SurePlan Y90 dosimetry software. Patients with excessive LSF were excluded. Post-therapy PET/CT scans were performed to assess the distribution and dosimetry of the Y-90 microspheres. Treatment response was evaluated using LIRADS and RECIST 1.1 criteria on follow-up triple-phase computed tomography. Results: Of the 44 patients, four were excluded owing to increased LSF (>20%), and two were diagnosed with intrahepatic cholangiocarcinoma. Of the remaining 38 HCC patients, six underwent streamlined TARE without LSF estimation, and the remaining 32 patients received standard scout dose–based dosimetry-guided treatment. The mean activity of the scout dose administered was 0.5 GBq (SD - 0.1). The mean pre-therapy LSF was 4.9 %, with a corresponding mean pre-therapy LD of 6.7 Gy. The mean treatment activity of Y-90 delivered was 3.27 GBq (SD-1.4) with a mean delivered tumor dose of 350.2 Gy (SD-165). The mean post-therapy LSF was 4.0 % with a corresponding LD of 5.4 Gy. A good correlation was observed between pre- and post-therapy LSF (r = 0.79, p < 0.01) and LD (r = 0.84, p < 0.01). At the time of analysis, follow-up imaging was available for 24 patients, demonstrating that 17 of them showed a complete response (LR-TR nonviable), 6 showed partial response (LR-TR viable), and one showed stable disease, resulting in an objective response rate (ORR) of 95.8%. Early adverse effects included fatigue, abdominal pain, nausea, vomiting, chest pain and fever, which were self-limiting. Four patients developed radiation-induced lung injury, and two developed acute liver failure. Conclusions: Y-90 TARE with pretreatment scout dose-based LSF estimation and individualized dosimetry is safe and feasible in real-world tertiary care practice. The encouraging ORR and correlation between pre- and post-therapy LSF and LD support the robustness of the dosimetry approach.