The method of tangential rotation therapy for non-operated breast cancer has been developed in Yonsei Cancer Center. This method is in principle to avoid the disorder of the lung field by radiotherapy as well as possible and to make an adequate radiation dosage according to each treated region, including breast, axilla, supra or infraclavicullar fossa, and sternum. We have various irradiation methods conducted today, but this continuous and repeated tangential rotation therapy is extraordinarily superior to a traditional fixed tangential therapy. The advantages of this method are summarized as follows: 1) Simultaneous treatment with different doses is possible to the breast and the thorax including the sternum. 2) The radiation effect on the intrathoracic organs including lung and heart is almost absent. 3) It is easy to simultoneous irradiation in the large treated region. 4) The dose distribution of various types is possible by changing a rotation angle and an eccentric angl in accordance with irradiated region. 5) The irradiated fields are not overlapped and not so complicated as a fixed polytagential therapy. Therefor the continuous and repeated tangential rotation therapy is an adequate method for the non-operated breast cancer and may be sure of helping for radiation therapy.