Yttrium-90 Ibritumomab Tiuxetan Doses Calculated to Deliver up to 15 Gy to Critical Organs May Be Safely Combined With High-Dose BEAM and Autologous Transplantation in Relapsed or Refractory B-Cell Non-Hodgkin's Lymphoma

To determine the maximum-tolerated radiation-absorbed dose (RAD) to critical organs delivered by yttrium-90 ((90)Y) ibritumomab tiuxetan in combination with high-dose carmustine, etoposide, cytarabine, and melphalan (BEAM) chemotherapy with autologous transplantation. Eligible patients had relapsed or refractory CD20+ non-Hodgkin's lymphoma (NHL). Individualized (90)Y activities were based on dosimetry and were calculated to deliver cohort-defined RAD (1 to 17 Gy) to critical organs with three to six patients per cohort. The therapeutic dose of (90)Y ibritumomab tiuxetan was followed by high-dose BEAM and autologous transplantation. Forty-four patients were treated. Thirty percent of patients had achieved less than a partial remission to their most recent therapy and would not have been eligible for autologous transplantation at most centers. The toxicity profile was similar to that associated with high-dose BEAM chemotherapy. Two dose-limiting toxicities occurred at the 17 Gy dose level, which made 15 Gy the recommended maximum-tolerated RAD. Although eight patients received at least twice the conventional dose of 0.4 mCi/kg, a weight-based strategy at 0.8 mCi/kg would have resulted in a wide range of RAD; nearly 25% of patient cases would have received 17 Gy or more, and many would have received less than 10 Gy. With a median follow-up of 33 months for all patients, the estimated 3-year progression-free and overall survivals were 43% and 60%, respectively. Dose-escalated (90)Y ibritumomab tiuxetan may be safely combined with high-dose BEAM with autologous transplantation and has the potential to be more effective than standard-dose radioimmunotherapy. Careful dosimetry is required to avoid toxicity and undertreatment.