The value of ¹⁸F-FAPI-04 PET/CT in the assessment of unresectable hepatocellular carcinoma after selective internal radiation therapy: a preliminary exploratory study.

Abstract

This study aimed to preliminarily evaluate the value of ¹⁸F-FAPI-04 PET/CT in assessing target lesions viability and treatment response in patients with unresectable hepatocellular carcinoma (uHCC) following Yttrium-90(⁹⁰Y) microsphere selective internal radiation therapy (SIRT). Patients with uHCC who underwent ⁹⁰Y-SIRT and subsequently received post-SIRT ¹⁸F-FDG and/or ¹⁸F-FAPI-04 PET/CT evaluations from February 2024 to June 2025 were retrospectively included. Visual assessments of post-SIRT target lesions were performed based on CECT/MRI, ¹⁸F-FDG PET/CT, and ¹⁸F-FAPI-04 PET/CT, and lesion detection efficacy was compared among the three methods. The SUV_max, peak standardized uptake value corrected for lean body mass (SUL_peak), metabolic/FAPI-avid tumor volumetric parameters of target and whole-body lesions before and after SIRT were measured, and the percentage changes (Δ%) were calculated. Post-SIRT response was assessed using mRECIST 1.1, ¹⁸F-FDG, and ¹⁸F-FAPI-04 PERCIST criteria. A total of 31 patients were included (mean age 51 ± 11, range: 38-75; males: 28). Post-SIRT ¹⁸F-FAPI-04 PET/CT showed comparable sensitivity to CECT/MRI for both target and all intrahepatic lesions (target lesions: 95.2% vs. 81.0%, all intrahepatic lesions: 80.0% vs. 88.2%, both P > 0.05), but lower specificity (target lesions: 64.3% vs. 100.0%, P = 0.063; intrahepatic lesions: 40.0% vs. 100.0%, P = 0.031). Compared with ¹⁸F-FDG PET/CT, ¹⁸F-FAPI-04 PET/CT had significantly higher sensitivity for detecting all intrahepatic lesions (78.9% vs. 55.3%, P = 0.023) but lower specificity (43.7% vs. 100.0%, P = 0.016). The concordance rates between ¹⁸F-FDG PERCIST and mRECIST were 69.2% and 71.4% for target and whole-body lesions, respectively; between ¹⁸F-FAPI-04 PERCIST and mRECIST, they were 73.3% and 75.0%, respectively. The mRECIST assessment results were significantly correlated with overall survival (OS), while ¹⁸F-FAPI-04 PET/CT PERCIST indicated that progressive patients had worse OS. Post-SIRT lesion uptake, FAPI-avid tumor volumetric parameters on ¹⁸F-FAPI-04 PET/CT, as well as ΔSUL_peak-target%, may have prognostic value. In uHCC patients undergoing ⁹⁰Y-SIRT,¹⁸F-FAPI-04 PET/CT shows high sensitivity but limited specificity for detecting post-SIRT intrahepatic lesions. Post-SIRT ¹⁸F-FAPI-04 PET/CT parameters may carry prognostic value. Chinese Clinical Trial Registry (ChiCTR2500107817), registered on 19 August 2025, retrospectively registered.