Prognostic Significance of Apparent Diffusion Coefficient in Hepatocellular Carcinoma Patients treated with Stereotactic Ablative Radiotherapy

The role of diffusion-weighted magnetic resonance imaging (DW MRI) in assessing durable tumor control for patients with hepatocellular carcinoma (HCC) treated with stereotactic ablative radiotherapy (SABR) was not defined. This retrospective study included 34 HCC patients with 45 lesions who had DW MRI data at baseline and within 6 months post-SABR. On the first post-SABR MRI, 13 lesions (28.9%) had a complete response (CR), 12 (26.7%) had a partial response (PR), 17 (37.8%) had stable disease, and 3 (6.7%) had progressive disease by modified Response Evaluation Criteria in Solid Tumors (mRECIST). On subsequent imaging, the response rate improved from 55.6% to 75.6%. The apparent diffusion coefficients (ADCs) (mean +/- standard deviation) pre-and post-SABR were 1.43 +/- 0.28 and 1.72 +/- 0.34 (x10(-3) mm(2)/s), respectively (p < 0.001). An ADC change = 25% (DW[+]) was identified as a predictor of favorable in-field control (IFC) (1-year IFC, 93.3% vs. 50.0% for DW[-], p = 0.004), but an mRECIST-based positive response (CR and PR) at the first MRI was not (p = 0.130). In conclusion, ADC change on early MRI is closely related to IFC in HCCs treated with SABR. Standardization of the DW MRI protocol, as well as prospective validation studies, are warranted.