Stereotactic ablative radiotherapy for patients with hepatocellular carcinoma: analysis of post-treatment radiology and explant histology.

Background: Stereotactic ablative radiotherapy (SABR) has emerged as a new treatment modality for hepatocellular carcinoma (HCC). Evaluation of tumour responses following SABR are currently based on conventional radiological criteria used for locoregional therapies. Whether these criteria accurately reflect tumour responses following SABR remains unknown. In this study, we provide a direct comparison of post-SABR radiological evaluation and explant histology for patients with HCC who underwent bridging SABR prior to liver transplantation.

Methods: Patients with HCC who received SABR as bridging therapy prior to liver transplantation (January 2016-December 2022) in a large UK liver transplant centre were included. Post-SABR imaging was reported by two specialist hepato-pancreato-biliary radiologists, and histological examination of the explanted liver was performed by experienced liver histopathologists.

Results: Six patients with residual active HCC received SABR as bridging therapy prior to undergoing liver transplantation in our cohort. Of five patients with viable HCC detected on explant histology, recent radiological evaluation using LI-RADS treatment response criteria had suggested no evidence of residual active HCC for three patients, difficulty delineating residual disease from post-radiotherapy changes for one patient, and accurately identified viable tumour in one patient.

Conclusion: In our case series conventional radiological criteria underestimated HCC tumour viability following SABR compared to explant histology. As the role for SABR expands in the management of HCC, caution is needed with radiological interpretation of HCC responses to radiotherapy using standard LI-RADS criteria. Prospective study in a larger cohort is required to identify radiological criteria capable of more conclusively evaluating HCC responses to SABR.