DOUBLE-TRACER DOSIMETRY OF ORGANS IN ASSESSMENT OF BONE-MARROW INVOLVEMENT BY 2 MONOCLONAL-ANTIBODIES

Five patients with ductal breast cancer were studied using simultaneou s administration of Tc-99(m)-labelled BW250/183 and I-131-labelled B72 .3 monoclonal antibodies (MAbs), The distribution and dosimetry of the se tracers were evaluated using the information from simultaneous ante rior and posterior whole body scintigrams, together with Tc-99(m) and I-131 standard activity sources, recorded on an average of 1, 4, 24, 9 0 and 224 h after injection, A method to eliminate I-131 scatter on Tc -99(m)-channel was developed, The geometric means of conjugate views a nd region-of-interest analysis were used to determine organ uptakes, m ean residence times and absorbed radiation dose estimates of organs in duced by the tracers, Organ uptakes (% of injected activity/ml) varied from 6.2 x 10(-3)/red marrow to 3.1 x 10(-2)/liver for Tc-99(m)-MAb a nd from 3.1 x 10(-2)/red marrow to 1.8 x 10(-1)/liver for I-131-MAb, o ne hour after injection, Calculated average residence times of organs for Tc-99(m)-labelled BW250/183 were in the range of physical mean-lif e of Tc-99(m) and from 71 to 95 h for I-131-B72.3 respectively. The av erage total absorbed dose from Tc-99(m)-MAb to the bone marrow was 0.0 1 and to the spleen 0.14 mGy/MBq and from I-131-MAb the corresponding values were 0.48 and 10.76 mGy/MBq. This double-tracer technique provi des information from two antibodies having different kinetic behaviour and may facilitate in distinguishing various antigens in targeting an d control MAb applications.