FEASIBILITY OF RADIOIMMUNOGUIDED SURGERY OF COLORECTAL-CARCINOMA USING INDIUM-111 CEA SPECIFIC ANTIBODY AND SIMULATION WITH A PHANTOM USING2 STEPS TARGETING WITH BISPECIFIC ANTIBODY

The study was undertaken to define the potential use of radiolabelled (Indium 111 or Technetium 99 m) carcinoembryonic antigen specific anti body (CEA f(ab')2) for the radioimmunodetection of colorectal cancer u sing an intraoperative hand-held gamma probe. A clinical study perform ed with ten patients showed that tumor with good uptake of CEA specifi c antibody could be detected with sufficient contrast only in two pati ents, Results of a biodistribution study performed with tumor fragment and normal tissue countings in a gamma counter showed high tumor upta ke in five patients, There was no correlation between tumor uptake and the count rates measured intraoperatively, To increase the signal/bac kground of the gamma probe, a simulation study with a peritoneal cavit y phantom was performed. We determined the efficiency of a two steps t argetting method compared to the direct method. We simulated different tumor sizes with plexiglas balls (0.5, 1, 2, 5 mi) and tested two sci ntillators (NaI, BgO). Experiments were performed with 111 In and 99 m Tc, The two steps targetting method was better than direct method. Th e results of simulation with direct method radiolabelled with 111 In c onfirmed our clinical study: no efficiency of a gamma probe for the su rgeon to detect a tumor. However the two steps targetting method (indi rect labelling method) was very encouraging to detect tumors (size 1 a nd 2 mi) and definitively convincing with 99 m Tc.