Methods: Carcinoembryonic antigen (CEA)–positive syngeneic breast and colon tumors in CEA transgenic animals were treated with single-dose IGRT (10 Gy) and 2 different regimens of fractionated IGRT (4 doses of 2.5 Gy or 4 doses of 3.65 Gy), with and without low-dose TAT (37 kBq of 225Ac-DOTA-anti-CEA) to optimize doses and tumor models for the combination of 2 types of IGRT plus TAT with immunocytokine therapy. The gene discussed is CEACAM5; the disease is neoplasm.