Table 1.
Characteristics of anti-CD20 radiolabelled monoclonal antibodies for radioimmunotherapy of CD20-positive B-cell ly mphomas
| Product | Y-90 ibritumomab tiuxetan | I-131 tositumomab |
|---|---|---|
| Radiolabelled MoAb | Mouse anti-CD20 | Mouse anti-CD20 |
| Isotope conjugation | Indirect: Y-90 chelated to tiuxetan which is covalently linked to antibody via arginine & lysine amino acids | Direct: I-131 iodination of tyrosine amino acids in the antibody |
| Therapeutic isotope | Yttrium-90 | Iodine-131 |
| Half-life | 2.6 days | 8 days |
| Emission path length and energy | 5 mm β, 2.29 mEv | 1 mm β, 0.616 mEv and γ, 0.36 mEv |
| Unlabelled MoAb given prior to radiolabelled MoAb | Chimeric rituximab 250 mg/m2 | Mouse tositumomab 450 mg |
| Tracer imaging dose | 5 mCi In-111 ibritumomab tiuxetan day 1 | 5 mCi I-131 tositumomab day 1 |
| Purpose of tracer/imaging dose | Imaging of biodistribution as additional safety measure | Determine retention and urinary clearance to calculate therapeutic dose |