ADC_total ratio and D ratio derived from intravoxel incoherent motion early after TACE are independent predictors for survival in hepatocellular carcinoma

Purpose: To explore the threshold of intravoxel incoherent motion (IVIM) parameters, apparent diffusion coefficient [ADC_total and ADC_(0,500) ] ratios 24-48 hours after transarterial chemoembolization (TACE) to assess early response in patients with unresectable hepatocellular carcinoma (HCC) and to compare the association between diffusion-weighted imaging with the intravoxel incoherent motion (IVIM-DWI) and mRECIST with survival.

Materials and methods: Institutional Review Board approval and informed consent were obtained for this prospective study. There were 30 patients undergoing 1.5T magnetic resonance imaging (MRI) with IVIM-DWI of 12 b values (0, 10, 20, 30, 40, 50, 70, 100, 200, 300, 500, 800 s/mm² ) 1 week before and 24-48 hours after TACE. Response was assessed with the change of true diffusion coefficient (D), pseudo-diffusion coefficient (D*), perfusion fraction (PF), ADC_total , and ADC_(0,500) values relative to baseline and with mRECIST. Receiver operating characteristic (ROC) curve analysis was used to explore the threshold of these parameters ratios. Kaplan-Meier, log-rank tests, and the Cox hazard model were used to correlate the response variables with progression-free survival (PFS) and to assess the incidence and potential clinical risk factors for PFS. Mann-Whitney U-test was used to compare the difference in parameters between different groups with progression within and beyond median PFS prior to TACE.

Results: Median PFS was 99 days, within which 16 patients progressed. The threshold of ADC_total ratio, D ratio, and ADC_(0,500) ratio were 13.1% (P = 0.001), 7.0% (P = 0.011), and 3.6% (P = 0.018) with sensitivity and specificity of 78.6% and 87.5%, 85.7% and 62.5%, 78.6% and 75%, respectively. The predictive utility of ADC_total ratio, D ratio, and ADC_(0,500) ratio for PFS were 0.848, 0.772, and 0.754, respectively. Survival analyses showed ADC_total ratio, D ratio, ADC_(0,500) ratio, liver cirrhosis, and mRECIST had a significant effect on PFS (P < 0.05). ADC_total ratio and D ratio were independent predictors for 99-day PFS (P = 0.025, P = 0.036). There were no significant differences in pretreatment IVIM-DWI parameters between PFS > 99-day group and PFS ≤ 99-day group with P values of 0.547 for D, 0.394 for D*, 0.575 for PF, 0.901 for ADC_(0,500) , and 0.506 for ADC_total , respectively.

Conclusion: The ADC_total ratio and D ratio 24-48 hours after TACE were independent predictors for response to TACE for HCC, and showed stronger association with PFS than mRECIST.

Level of evidence: 1 Technical Efficacy: Stage 2 J. MAGN. RESON. IMAGING 2017;46:820-830.