Tumor response after yttrium-90 radioembolization for hepatocellular carcinoma: Comparison of diffusion-weighted functional MR imaging with anatomic MR imaging

PURPOSE: Anatomic magnetic resonance (MR) imaging assessment of hepatocellular carcinoma (HCC) response to yttrium-90 (Y-90) radioembolization may require 3 months before therapeutic effectiveness can be determined. The relationship between anatomic MR and diffusion-weighted imaging (DWI) changes after Y-90 therapy is unclear. The present study tested the hypothesis that apparent diffusion coefficient (ADC) values on DWI at 1 month precede anatomic tumor size change at 3 months after Y-90 radioembolization. MATERIALS AND METHODS: In this prospective study, 20 patients with HCC (16 men) enrolled between April 2005 and July 2006 underwent lobar Y-90 therapy with mean doses of 141 Gy (right lobe) and 98 Gy (left lobe). Anatomic 1.5-T MR imaging (gadolinium-enhanced T1-weighted gradient-recalled echo) and DWI (single-shot spin-echo echo-planar imaging; b value of 0, 500 sec/mm(2)) were performed at baseline (0-3 weeks before 9 Y therapy) and at 1 and 3 months after 9 Y therapy. Tumor size and ADC values were measured and compared, and the percentage change in ADC was compared to the change in tumor size (minimum > 5% change in size), with use of a paired t test (alpha = .05). RESULTS: Yttrium-90 therapy was successfully delivered in all patients. The mean baseline ADC of 1.64 x 10(-3) mm(2)/sec +/- 0.30 significantly increased to 1.81 x 10(-3) mm(2)/sec +/- 0.37 at 1 month (P = .02), and to 1.82 x 10(-3) mm(2)/sec +/- 0.23 at 3 months (P = .02). The mean baseline tumor size of 83.0 cm(2) +/- 63.7 did not change statistically at 1 month (84.1 cm(2) +/- 62.1; P = .75) or 3 months (74.0 cm(2) +/- 57.0; P = .10). The overall mean ADC percentage change at 1 month of 10.5% +/- 23.1% preceded an overall mean tumor size percentage change at 3 months of -18.5% +/- 31.5% (P = .03). CONCLUSIONS: HCC tumor response assessed with DWI at 1 month preceded anatomic size changes at 3 months after 9 Y therapy. DWI may assist in early determination of the response or failure of 9 Y therapy for HCC.