Loss of diffusion restriction and arterial enhancement accurately predicts 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 reliably predict CPN post SIRT; persistent diffusion restriction despite the findings of mRECIST CR appears to correlate with residual disease.