An immunoconjugate of the monoclonal antibody ibritumomab conjugated with the linker-chelator tiuxetan, a high affinity, conformationally restricted chelation site for radioisotopes. When bound to indium In 111 or yttrium Y 90, ibritumomab tiuxetan, targeting the CD20 antigen on B cell surfaces, specifically delivers a potentially cytotoxic dose of radiation to B lymphocytes. Ibritumomab is a murine IgG1 kappa monoclonal antibody directed against the CD20 antigen, which is found on the surface of normal and malignant B lymphocytes. or A monoclonal antibody that is used to treat certain types of B-cell non-Hodgkin lymphoma and is being studied in the treatment and detection of other types of B-cell tumors. Monoclonal antibodies are made in the laboratory and can locate and bind to substances in the body, including cancer cells. Ibritumomab binds to the protein called CD20, which is found on B cells. It is linked to the compound tiuxetan. This allows certain radioisotopes to be attached before it is given to a patient. It is a type of monoclonal antibody-chelator conjugate. Also called Zevalin.