Dosimetry in patients with B-cell lymphoma treated with [90Y]ibritumomab tiuxetan or [131I]tositumomab.

Radioimmunotherapy involves the use of radiolabeled monoclonal antibodies (MAbs) to treat malignancy. The therapeutic effect is determined by the radiopharmaceutical, the radiation absorbed dose and previous treatments. There are currently two approved radiopharmaceuticals for the treatment of B-cell lymphoma - the 90Y-labeled ibritumomab and the 131I-labeled tositumomab. Both are directed against CD20, albeit not against the same epitope. This paper summarizes current results of dose-responses for normal tissues and tumours of [131I]tositumomab and [90Y]ibritumomab tiuxetan, discusses them in the context of dosimetry methods used and highlights the assumptions being made in the different dosimetry methodologies. Moreover, we wish to point at the possibility of performing low-cost therapy bremsstrahlung imaging for [90Y]ibritumomab tiuxetan to confirm biodistribution, and possibly also for dosimetric calculations.