Tumor response assessment by MRI following stereotactic body radiation therapy for hepatocellular carcinoma.

BACKGROUND: To evaluate the MRI features of a tumor response, local control, and predictive factors of local control after stereotactic body radiation therapy (SBRT) for hepatocellular carcinoma (HCC).

METHODS: Thirty-five consecutive patients with 48 HCCs who were treated by SBRT were included in this retrospective study. All patients provided written informed consent to be treated by SBRT, and prior to inclusion they authorized use of the treatment data for further studies. The assessment was made using MRI, with determination of local and hepatic responses according to Response Evaluation Criteria in Solid Tumors (RECIST) and modified RECIST (mRECIST) criteria during a two-year follow-up.

RESULTS: The local response rate according to mRECIST was higher than with RECIST. A tumor diameter less than 20 mm at baseline was an independent predictive factor for RECIST and mRECIST responses, as was diffusion-weighted signal for RECIST. During follow-up, a tumor diameter of <20 mm (p = 0.034) and absence of a high intensity on T2-weighted (p = 0.006) and diffusion-weighted images (p = 0.039) were associated with a better response according to RECIST. Post-treatment changes include peritumoral ring-like enhanced changes with high intensity on T2-weighted images.

CONCLUSIONS: SBRT is a promising technique for the treatment of inoperable HCC. Post-treatment changes on MRI images can resemble tumor progression and as such must be adequately distinguished. The regression of tumorous enhancement is variable over time, although diffusion-weighted and T2-weighted intensities are predictive factors for tumor RECIST responses on subsequent MRIs. They hence provide a way to reliably predict treatment responses.