A targeted radioimmunoconjugate composed of a murine monoclonal anti-CD20 antibody (ibritumomab) linked by a chelator (tiuxetan) to the imaging radioisotope indium-111. This radioimmunoconjugate binds to CD20-positive cells, permitting radioimmuno-localization of CD20-positive cell biodistribution. orA radiolabeled monoclonal antibody that is used to detect certain types of B-cell non-Hodgkin lymphoma and is being studied in the detection of other types of B-cell tumors. It is made up of the monoclonal antibody ibritumomab plus the radioisotope indium 111. It binds to the protein called CD20, which is found on B cells. A machine is used to detect which cells in the body have bound the antibody. Indium In 111 ibritumomab tiuxetan is a type of radiopharmaceutical. Also called In 111 ibritumomab tiuxetan and In 111 Zevalin.