Loss of both diffusion restriction and arterial enhancement can predict complete pathological response following Y-90 selective internal radiation therapy for hepatocellular carcinoma

PURPOSE: To assess the association of diffusion restriction on diffusion weighted MRI (DWI) with complete pathological necrosis (CPN) in hepatocellular carcinoma (HCC) following selective internal radiation therapy with Yttrium-90 resin microspheres (SIRT). METHODS: A retrospective cohort study of patients undergoing resection or transplantation for HCC following SIRT was performed. Imaging pre- and post-SIRT was assessed for response to treatment via mRECIST and for the presence of diffusion restriction on DWI. Histological specimens were assessed for complete pathological necrosis (CPN). RESULTS: Twenty-nine tumours were included from 25 patients; mRECIST complete response (CR) demonstrated moderate reliability (sensitivity 0.92, specificity 0.68) for predicting CPN. Twelve tumours did not have diffusion restriction on pretreatment DWI; following their exclusion, loss of diffusion restriction demonstrated a weak agreement (sensitivity 0.85, specificity 0.80, Cohen's Kappa 0.197) for prediction of CPN. The combination of mRECIST CR and loss of diffusion restriction was associated with CPN in 100% (6/6) cases; whilst persistent abnormal diffusion restriction despite mRECIST CR was associated with residual disease in 75% (3/4) cases. CONCLUSION: The combination of mRECIST CR when combined with loss of diffusion restriction appears to predict CPN post SIRT; persistent diffusion restriction despite the findings of mRECIST CR appears to correlate with residual disease.