Evaluation of different beta-counting systems involved in 90Y-Zevalin quality control

90Y-ibritumomab tiuxetan (90Y-Zevalin) is currently approved for radioimmunotherapy of patients with relapsed or refractory low-grade, follicular, or transformed B-cell non-Hodgkin's lymphoma. The radioimmunoconjugate may be administered to the patient only if the radiolabelling yield is higher than 95%.

To evaluate different methods of quality control testing for an accurate and rapid determination of radiolabelling yield in the clinical routine.

Five beta-counting systems, involved in determining the yield of radiolabelled 90Y-Zevalin, were compared: an autoradiography system (AS), a thin-layer chromatography (TLC) scanner system, a dose calibrator (DC), a liquid scintillation analyser (LSA) and high-performance liquid chromatography (HPLC). These instruments were also analysed in terms of efficiency, spatial resolution, analysis time, operating procedure level, cost and availability.

Radiolabelling yields were comparable among all instruments except for DC whose values were dubious. Efficiency was 1.5+/-0.11 MDLU.s for the AS (where DLU means digital light unit), 3.5+/-0.2 kcps for the TLC analyser, 0.74+/-0.02 MBq for the DC, 15+/-0.12 kcps for LSA and 180+/-0.07 kcps for HPLC. Spatial resolution was 1 mm for AS and 5 mm for the TLC analyser. The quality control test needed 8 min with AS and DC, 15 min with TLC and LSA, and 50 min with HPLC.

The short analysis time, high sensitivity, simultaneous detection of multiple radioactive strips and low cost offered by AS make it a suitable tool for radioactivity analysis and quantification in a radiopharmacy laboratory.