A monoclonal antibody (tositumomab) that has been chemically changed by adding radioactive iodine, and that is used in the treatment of certain types of non-Hodgkin lymphoma. It belongs to the family of drugs called radioconjugated monoclonal antibodies. When iodine I 131 tositumomab and tositumomab are given together, the combination is called the Bexxar regimen. Also called Bexxar regimen, tositumomab, and tositumomab and iodine I 131 tositumomab.