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

ABSTRACT

PURPOSE: Anatomic magnetic resonance (MR) imaging assessment of hepatocellular carcinoma (HCC) response to yttrium-90 ((90)Y) radioembolization may require 3 months before therapeutic effectiveness can be determined. The relationship between anatomic MR and diffusion-weighted imaging (DWI) changes after (90)Y 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 (90)Y radioembolization. MATERIALS AND METHODS: In this prospective study, 20 patients with HCC (16 men) enrolled between April 2005 and July 2006 underwent lobar (90)Y 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 (90)Y therapy) and at 1 and 3 months after (90)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 (90)Y therapy. DWI may assist in early determination of the response or failure of (90)Y therapy for HCC.