Administered activity and outcomes of glass versus resin (90)Y microsphere radioembolization in patients with colorectal liver metastases

Given the differences in size, specific activity, and dosing methods for glass yttrium-90 microspheres ((90)Y-glass) and resin (90)Y microspheres ((90)Y-resin), these therapies may expose the liver to different amounts of radiation, thereby affecting their efficacy and tolerability. We aimed to compare the prescribed activity of (90)Y-glass and (90)Y-resin for real-world patients undergoing selective internal radiation therapy (SIRT) for liver-dominant metastatic colorectal cancer (mCRC) and to assess efficacy and safety outcomes in these patients. We examined the records of 28 consecutive patients with unresectable colorectal liver metastases treated with SIRT between June 2008 and May 2011 at our institution. Using baseline CT and MR images, we calculated a projected activity as if we had used the other product and compared it to the actual prescribed activity of (90)Y-glass and (90)Y-resin for each SIRT treatment per manufacturer guidelines. Progression and adverse events were evaluated at follow up visits. Survival was analyzed by the Kaplan-Meier method. For (90)Y-glass treatments with a mean prescribed (90)Y activity of 1.77 GBq, the mean projected (90)Y-resin activity was 0.84 GBq. For (90)Y-resin treatments with a mean prescribed (90)Y activity of 1.05 GBq, the mean projected (90)Y-glass activity was 2.48 GBq. The median survival was 9.3 months versus 18.2 months for (90)Y-glass and (90)Y-resin, respectively (P=0.292). During the second year after SIRT, the hazard ratio of death for patients treated with (90)Y-glass versus (90)Y-resin was 4.0 (95% CI: 1.3, 12.3; P=0.017). No significant difference in progression, adverse events or liver toxicity was observed. Using manufacturer recommended guidelines, (90)Y-resin delivers significantly less activity than (90)Y-glass to patients with liver-dominant mCRC undergoing SIRT with no significant difference in adverse events and a trend toward improved survival.