Dosimetry with (188)Re-labelled monoclonal anti-CD66 antibodies. A simplified approach based on a single measurement 3 h p.i.
AIM: For the therapeutic application of radiopharmaceuticals the activity is determined on an individual basis. Here we investigated the accuracy for a simplified assessment of the residence times for a (188)Re-labelled anti-CD66 monoclonal antibody. PATIENTS, METHODS: For 49 patients with high risk leukaemia (24 men, 25 women, age: 44 +/- 12 years) the residence times were determined for the injected (188)Re-labelled anti-CD66 antibodies (1.3 +/- 0.4 GBq, 5-7 GBq/mg protein, >95% (188)Re bound to the antibody) based on 5 measurements (1.5, 3, 20, 26, and 44 h p.i.) using planar conjugate view gamma camera images (complete method). In a simplified method the residence times were calculated based on a single measurement 3 h p.i. RESULTS: The residence times for kidneys, liver, red bone marrow, spleen and remainder of body for the complete method were 0.4 +/- 0.2 h, 1.9 +/- 0.8 h, 7.8 +/- 2.1 h, 0.6 +/- 0.3 h and 8.6 +/- 2.1 h, respectively. For all organs a linear correlation exists between the residence times of the complete method and the simplified method with the slopes (correlation coefficients R > 0.89) of 0.89, 0.99, 1.23, 1.13 and 1.09 for kidneys, liver, red bone marrow, spleen and remainder of body, respectively. CONCLUSION: The proposed approach allows reliable prediction of biokinetics of (188)Re-labelled anti-CD66 monoclonal antibody biodistribution with a single study. Efficient pretherapeutic estimation of organ absorbed dose may be possible, provided that a more stable anti-CD66 antibody preparation is available.