Efficacy and dosimetry of yttrium-90 radiation segmentectomy for unresectable hepatocellular carcinoma: A retrospective study in China.

e14555 Background: Radiation segmentectomy (RS) with yttrium-90 ( 90 Y) microspheres has evolved as a targeted ablative approach for hepatocellular carcinoma (HCC). However, real-world evidence on its efficacy and dosimetric correlates remains limited in Chinese patients. This study assesses clinical outcomes and dosimetry of Radiation segmentectomy in unresectable HCC. Methods: We retrospectively analyzed patients with hepatocellular carcinoma (HCC) who received 90 Y - RS at our center between June 2022 and October 2025. The primary endpoint was objective response rate (ORR). Secondary endpoints included disease control rate (DCR), downstaging rate, and safety. Tumor response was assessed using mRECIST criteria, and adverse events were graded according to CTCAE v5.0. Results: 50 patients were included and were followed more than 3 months. The baseline characteristics of the patients are shown in the Table. The median age was 55 years (IQR, 50-59 years) and 84% of patients were male. Hepatitis B infection was common (84%),. The median diameter of solitary lesions was 82.2 mm（IQR 57.5-103.9 mm), median maximum tumor diameter was 60.86 mm (IQR 43.7-94.5 mm), with 78% having tumors > 5 cm and 56% having ≥3 lesions. BCLC staging distribution was A (12%), B (24%), and C (64%). Portal vein tumor thrombus was observed in 54% of patients, and 36% had extrahepatic lymph node metastases. The median 90 Y dose was 2 GBq (IQR, 1.3–3.2 GBq), delivering a median radiation dose of 243 Gy (IQR, 200–300 Gy) to the target tissue. Most patients (72%) received concomitant systemic therapy. Treatment responses according to mRECIST criteria showed an objective response rate (ORR) of 74% and disease control rate (DCR) of 82%, with complete response (CR) rate of 52.0% and partial response (PR) rate of 22%. Notably, 58% of patients achieved downstaging, with 11 patients (22%) undergoing potentially curative procedures (5 resections, 6 liver transplants). Treatment was well tolerated, with no grade ≥3 adverse events reported. Additionally, a tumor dose threshold of 215.5 Gy was identified as a predictor of objective response (AUC = 0.69). Conclusions: In this retrospective study, Yttrium-90 radiation segmentectomy demonstrated favorable safety and efficacy in Chinese patients，achieving an impressive objective response rate (ORR) of and a substantial downstaging rate. A tumor dose threshold of 215.5 Gy was identified as a predictor of treatment response. Patient Characteristics (N=50) Median IQR 25, 75 or n (%) Age, years 55 49.5 - 58.5 Diameter of solitary lesions 82.2 57.5 - 103.9 Max tumor diameter, mm 60.9 43.7 - 94.5 Number of tumors > 3 28 (56%) PVTT 27 (54%) AFP, ng/mL 286.4 16.3 - 1001.2 Treatment Responses (mRECIST) Objective Response Rate 74% Disease control rate 82%