Purpose: Radioimmunotherapy with anti-CD20 antibodies (Abs) labeled with β-emitters is now used in the treatment of non-Hodgkin's lymphoma (NHL). Because 90Y is a pure β-emitter, no direct image of its distribution can be obtained in humans. In this paper, we present in this study imaging data of 90Y-Ab distribution in human-mantle-cell lymphoma within a mouse model. Describing the actual distribution of the radionuclide at the level of particles range may have important impact on patient dosimetry and therapy treatment planning. Experimental Design: NOD/SCID mice were grafted with a human NHL cell line that involves the bone marrow. The mice were treated with 90Y-ibritumomab tiuxetan (Zevalin®; Schering AG, Germany) and sacrificed 2 hours after Zevalin administration. Tissue sections were then prepared and viewed under conventional microscopy. The distribution of the radioactivity in mouse femur was determined by using digital autoradiography and subsequently correlated with immunohistochemical results. Results: Various extent of bone marrow infiltration was investigated and found to be reproducible. Zevalin uptake was heterogeneous within the bone marrow. However, unspecific mouse monoclonal uptake by accessory myeloid cells gave nonspecific background radioactivity. Treating mice with an irrelevant mouse IgG1 monoclonal antibody (mAb) before Zevalin injection controlled this unspecific uptake, and images were strongly correlated with bone marrow infiltration on histologic analysis. Conclusions: Our model was reproducible, and allows for the study of various bone marrow involvement with good sensitivity. We demonstrated that imaging of the β-emitter was possible with good image quality and that 90Y-Zevalin is distributed heterogeneously within bone marrow. These data suggest that detailed pharmacokinetics may be developed with this model.
