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

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We combined external beam radiotherapy (EBRT) with yttrium-90 ibritumomab tiuxetan ((90)Y-IT) in an attempt to improve therapeutic response in patients with relapsed or refractory bulky follicular lymphoma (RRBFL). Between February 2006 and September 2007, 11 patients with RRBFL were treated with EBRT followed by (90)Y-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), (90)Y-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 (90)Y-IT. Only 2 patients required prolonged breaks between EBRT and (90)Y-IT. The median time after (90)Y-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 (90)Y-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. In contrast to prior failure analysis data for RRBFL patients treated with (90)Y-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 (90)Y-IT.