Radioimmunoguided brachytherapy (Rigby): A new technique for implantation of occult tumors

The traditional methods of brachytherapy use inspection, palpation, and radiological imaging studies for defining the tumor volume for implantation. If there is only occult disease after resection, demarcation of the tumor volume by traditional techniques is not possible. The radioimmunoguided brachytherapy (RIGBY) technique was therefore developed to address this need. I-125 radiolabelled CC-49 monoclonal antibody (MAb) was injected intravenously into patients with metastatic colorectal cancer 3 weeks before surgery. Gross metastatic disease in the liver, pelvis, retroperitoneum, brain etc., was resected using the Radioimmunoguided(TM) Surgery (RIGS(R)) technique. Occult residual or microscopic disease detected by the hand-held gamma-detecting probe (GDP) was precisely implanted with 160 Gy of Iodine-125, 120 Gy of Palladium-103, or 60 Gy of Iridium-192 brachytherapy. The RIGBY technique has been used in 28 patients during the last two years. Extended demarcation of margins and delineation of tumor volume was achieved in 25 of the 28 patients allowing more complete treatment of residual tumor. The RIGBY technique could not be used to define the tumor margin in 3 patients because the MAb did not localize in the tumor. This preliminary report addresses primarily the technique and not the efficacy or morbidity.