| Summary: | 90Y-ibritumomab tiuxetan (Zevalin) and 131I-tositumomab (Bexxar) are current choices for radioimmunotherapy (RIT) of patients with follicular rituximab-relapsed or refractory CD20+ follicular B-cell NHL. Bexxar is available in the United States and Canada, while Zevalin was approved for use only in Europe. The Zevalin regimen consists of rituximab ('cold', chimeric antibody) and 90Y-ibritumomab tiuxetan ('hot' antibody). In Bexxar regimen, a tositumomab (murine antibody) is used as both, the unlabelled and labelled antibody. In both cases, the therapeutic infusion of 'hot' or radiolabelled component is preceded one week earlier by an infusion of a 'cold' or unlabelled antibody. In the US, the whole-body scanning using 111In-ibritumomab following the initial rituximab infusion is required for determination of biodistribution before the therapeutic dose of Zevalin. Bexxar regimen includes three whole body scans during the week after an imaging dose of 131I-tositumomab, which are necessary for calculation of the therapeutic dose of 131I-tositumomab. For each regimen, patients with a platelet count ≥150x109/L receive a full therapeutic dose, whereas patients with platelet counts >100x109/L<150x109/L receive a modified dose of radiolabelled antibody. Therapeutic dose of Zevalin is 11-15 MBq/kg (up to maximum of 1200 MBq), while the dose of Bexxar is 1.85-5.55 GBq (maximal tolerated absorbed dose for the whole body is 75cGy). If compared to alternative treatments, the radioimmunotherapy with Bexxar and Zevalin achieves longer time to progression and longer duration of response with overall response rate between 80% to almost 100%. Repeated treatment with Zevalin or Bexxar is possible. The additional subsequent conventional therapy is compatible. Radioimmunotherapy is radiation safe and well tolerated treatment with primarily transient haematological adverse events. Pregnancy and lactation are contraindications for radioimmunotherapy. Beta radiation of 90Y allows treatment on outpatient basis.
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