Prediction of Recurrence of Hepatocellular Carcinoma Following Radiation Segmentectomy with Resin Microspheres Based on Underdosed Tumor Volume on Yttrium-90 Positron Emission Tomography/CT Dosimetry

Purpose: To evaluate the use of immediate post–yttrium-90 (⁹⁰Y)-radiation segmentectomy (RS) positron emission tomography (PET)/computed tomography (CT) and dosimetry software in predicting incomplete response in early-stage hepatocellular carcinoma (HCC). Materials and Methods: Patients with early-stage HCC undergoing resin ⁹⁰Y-RS (July 2014 to December 2022) prescribed using the single-compartment Medical Internal Radiation Dose (MIRD) model with post–⁹⁰Y transarterial radioembolization (TARE) PET/CT were reviewed. Forty patients (42 HCCs; 69 years [interquartile range {IQR}, 63–77]; male, 75%), with a median tumor size of 3.4 cm (IQR, 2.2–4.6) met criteria. Dose-volume histograms were generated using dosimetry software (MIM SurePlan LiverY90, v7.2.3). Modified Response Evaluation Criteria in Solid Tumours (mRECIST) treatment responses were correlated with quantitative volumetric analyses of tumor absorbed dose (TAD) and underdosed tumor volume, defined as volume of tumor receiving less than 100 Gy (V_0–100). Additional subgroup dosimetry analysis was performed between tumors with complete response (CR) and incomplete response. Results: Tumors treated showed 86% CR and 100% objective response rate at 6-month follow-up. Subgroup analysis between CRs and incomplete responders showed no difference in tumor size, volume, prescribed tissue dose, or prescribed, delivered, or specific activity. Incomplete responders had a lower D₅₀ than CRs (162 vs 273 Gy, P = .040), lower particle density (36,310 vs 66,980 particles/cm³, P = .040), and higher absolute (10 vs 0.7 mL; P = .011) and proportion (33% vs 5%; P = .001) of underdosed tumor volumes (V_0–100). An underdosed tumor volume (V_0–100) of ≥28% had an increased likelihood of incomplete response (odds ratio, 75; P = .001). Conclusions: ⁹⁰Y-TARE PET/CT can identify tumors incompletely treated with an ablative ⁹⁰Y-RS dose and guide decision for closer follow-up or early retreatment.