[68Ga] Ga-FAPI positron emission tomography/computed tomography uptake following liver stereotactic body radiation therapy in hepatocellular carcinoma: two case reports

BACKGROUND: [⁶⁸Ga]Ga-FAPI Positron Emission Tomography/Computed Tomography have shown high sensitivity for detecting hepatocellular carcinoma (HCC). [⁶⁸Ga]Ga-FAPI uptake also occurs in benign fibroinflammatory processes, creating a specific challenge for post-treatment surveillance after liver-directed therapies. CASE PRESENTATION: We report two HCC patients who underwent stereotactic body radiation therapy (SBRT) and subsequently developed FAPI-avid hepatic lesions. In Case 1, a 68-year-old man showed focal FAPI uptake in segment VI following SBRT, which Magnetic Resonance Imaging (MRI) characterised as fibrosis (LI-RADS LR-TR non-viable), with stable tumour markers and no clinical progression. In Case 2, a 77-year-old man exhibited FAPI avidity in the treated lesion, with MRI findings suggestive of post-treatment change. In both cases, the increased FAPI uptake was deemed as false-positive and attributed to post-radiation fibroinflammatory changes. CONCLUSION: These cases highlight a critical interpretative limitation of [⁶⁸Ga]Ga-FAPI PET/CT in post-SBRT HCC surveillance. Fibroblast activation in healing tissues can mimic recurrence; MRI correlation should be done to prevent misdiagnosis. Our report provides novel evidence that SBRT-induced hepatic fibrosis may confound FAPI-based imaging and adds to the evolving understanding of FAPI's performance in surveillance of liver malignancies.