External Beam Radiotherapy Followed by 90Y Ibritumomab Tiuxetan in Relapsed or Refractory Bulky Follicular Lymphoma

Purpose: We combined external beam radiotherapy (EBRT) with yttrium-90 ibritumomab tiuxetan (90Y-IT) in an attempt to improve therapeutic response in patients with relapsed or refractory bulky follicular lymphoma (RRBFL). Methods and Materials: Between February 2006 and September 2007, 11 patients with RRBFL were treated with EBRT followed by 90Y-IT. Bulky disease (BD) was defined as >5 cm. EBRT was delivered to BD as 2,400 cGy in eight fractions using computed tomography (CT)-based planning. BD was contoured as the gross tumor volume. A planning margin of 1 to 2 cm was added depending on anatomical location. After recovery of complete blood counts (CBC), 90Y-IT was administered at a dose of 0.3 or 0.4 mCi/kg depending on platelet counts. Hematologic toxicity was monitored through weekly CBC. Response was measured by positron emission tomography/CT or CT 3-4 months after 90Y-IT. Results: Only 2 patients required prolonged breaks between EBRT and 90Y-IT. The median time after 90Y-IT for platelets to recover to >100,000/ml was 55 days (range, 41-128 days). Platelet counts for 1 patient, who had received 4 previous chemotherapy regimens, never reached 100,000/ml. The complete and overall responses to combined therapy as measured 3-4 months after 90Y-IT were 64%. No patients relapsed within the EBRT field. With a median follow-up of 36.1 months, 6 patients have relapsed, 2 of whom have died. Median progression-free survival was 17.5 months. Conclusions: In contrast to prior failure analysis data for RRBFL patients treated with 90Y-IT alone, a brief course of EBRT prevented relapse in sites of BD. EBRT used to pretreat bulky sites may improve clinical outcomes and potentially extend survival when combined with 90Y-IT.