Splenic irradiation in chronic myelogenous leukemia is reserved for patients who have painful splenomegaly despite chemotherapy and/or inoperable splenomegaly because of huge size. The role of splenic irradiation is diminution of painful splenomegaly and indirect effect of splenic irradiation on unirradiated hematopoietic and lymphoreticular tissue such as reduction of leukocyte count and increase of hemoglobin level. We report on a useful clinical method for splenic irradiation in chronic myelogenous leukemia. We have used sonography as the tool of simulation. The portal size using modified method is smaller than the field size of conventional simulation, and so this method suggests that useful to irradiation of huge splenomegaly, effective shielding of critical organ and the downfall of complication during irradiation of spleen.