Evaluation of early treatment response to radiotherapy for HCC using pre- and post-treatment MRI

Background: Stereotactic body radiation therapy is an emerging treatment option for patients with unresectable advanced hepatocellular carcinoma (HCC). Because liver parenchyma neighboring the tumor is unavoidably exposed to irradiation, evaluation of treatment response following radiotherapy for HCC is challenging due to increased peritumoral arterial hyperemia and delayed clearance of contrast agent in the tumor. Purpose: To explore which change of magnetic resonance imaging (MRI) features between pre- and post-radiotherapy could help evaluate viability of HCC. Material and Methods: Thirty-nine patients who underwent MRI before and immediately after radiotherapy for HCC were enrolled. Imaging features were assessed before and within three months after radiotherapy and changes of those imaging features were correlated with (i) tumor response at six months after radiotherapy and (ii) time to progression (TTP). Results: On post-radiotherapy MRI, the short-term responders showed significantly higher incidence of negative typical HCC features including arterial enhancement with washout (P = 0.032), hyper-intense T2 signal intensity (P = 0.021), and hyper-intensity on DWI (P < 0.001). On multivariate Cox hazard analysis to estimate TTP, hazard ratios of modified RECIST and disappearance of arterial enhancement with washout were 2.18 and 2.79 (P = 0.087 and 0.029, respectively). Conclusion: Disappearance of arterial enhancement with washout on post-radiotherapy would be strong features for prediction of treatment response after radiotherapy of HCC.