Iodine-131 tositumomab (Bexxar) in a radiation oncology environment

Abstract

Iodine-131 (I-131) tositumomab (Bexxar; GlaxoSmithKline, Research Triangle Park, NC) is one of two recently approved radiolabeled antibodies directed against the CD20 surface antigen found on normal B cells and in more than 95% of B cell non-Hodgkin's lymphoma. The compound itself is formulated as an IgG2a immunoglobulin radiolabeled with the mixed beta/gamma emitter I-131. Multicenter clinical trials have repeatedly shown impressive clinical responses (20-40% complete response rates and 60-80% overall response rates) in the patient groups for whom this treatment is indicated. Treatment-related toxicity is generally extremely mild and typically involves only reversible hematopoietic suppression and (in some cases) a risk of treatment-induced hypothyroidism. Owing to the radiation safety concerns necessitated by the clinical use of this targeted radiopharmaceutical, it is important for radiation oncology departments wishing to participate in the care of these patients to establish methodologies and standard operating procedures for safe and efficient departmental use. This summary reviews the pertinent background information related to the current clinical experience with I-131 tositumomab and highlights some of the major opportunities for the participation of radiation oncology in the patient evaluation and treatment process. I-131 tositumomab provides an excellent example of the way in which the increasingly important new field of "targeted therapy" intersects with the practice of clinical radiotherapy. The author contends that it will be worth the time and effort involved in establishing a firm basis for the development of a comprehensive program for systemic targeted radiopharmaceutical therapies (STaRT) within the radiation medicine domain.