Assessment of viable tumours by [Ga]Ga-FAPI-04 PET/CT after local regional treatment in patients with hepatocellular carcinoma.

Purpose: To investigate the efficacy of [Ga]Ga-FAPI-04 PET/CT for assessing viable tumours (VTs) after local regional treatment (LRT) in hepatocellular carcinoma (HCC) patients. The related imaging features of HCC after LRT are preliminarily discussed.

Methods: A cohort of 37 LRT patients with HCC (encompassing 51 lesions) was retrospectively included from a prospective parent study (ChiCTR2000039099), and sequential PET/CT using [F]FDG and [Ga]Ga-FAPI-04 was performed. The diagnostic accuracies of [Ga]Ga-FAPI-04 and [F]FDG PET/CT and multiphasic CT/MRI for detecting VTs after LRT were calculated and analysed. Pathological examination was considered the gold standard for VT diagnosis, and clinical follow-up was used as the reference standard. The SUVmax and tumour-to-background ratio (TBR) derived from [F]FDG and [Ga]Ga-FAPI-04 PET/CT were calculated and compared. Moreover, the SUVmax, target-to-normal liver ratio (TNR) of VT, tumour necrosis (TN), benign rim (BR), and normal liver (NL) from different imaging modalities after LRT for HCC were compared.

Results: Both the sensitivity (96.0% [24/25] vs. 36.0% [9/25], p < 0.001) and accuracy (94.1%, [48/51] vs. 68.6% [35/51], p = 0.004) of [Ga]Ga-FAPI-04 PET/CT for detecting VTs after LRT were greater than those of [F]FDG PET/CT, whereas their specificities were comparable (92.3% [24/26] vs. 100% [26/26]). Notably, [Ga]Ga-FAPI-04 PET/CT had a greater SUVmax (9.80 vs. 3.60) and TBR (9.93 vs. 1.57) than [F]FDG PET/CT in VT patients (all p < 0.001). Furthermore, VT had a greater SUVmax and TNR than did TN, BR, and NL on [Ga]Ga-FAPI-04 PET/CT (all p < 0.001) and exhibited morphologic nodular, mass-like, or irregular tracer uptake. Although no significant differences were observed for VT detection (all p > 0.05), [Ga]Ga-FAPI-04 PET/CT and multiphasic CT/MRI complemented each other in some cases.

Conclusion: [Ga]Ga-FAPI-04 PET/CT not only presented higher sensitivity and accuracy than [F]FDG PET/CT for diagnosing VTs after LRT for HCC but also showed comparable diagnostic accuracy and complementary roles with multiphasic CT/MRI. Overall, [Ga]Ga-FAPI-04 PET/CT may play an essential role in surveillance after LRT for HCC.

Trial Registration: Chinese Clinical Trial Registry ChiCTR2000039099. Registered 17 October 2020.