Abstract: A method of treatment of breast cancer using a brachytherapy radiation source. A tumor is surgically removed from the breast, creating thereby a cavity, and an autologous fat pad, preferably an abdominal fat pad is transplanted under the surface of the skin within the cavity. A brachytherapy balloon catheter is then inserted through the skin of the patient into the cavity and inflated, and a radiation source is deposited into the balloon for treatment, with the fat pad creating a cushion of at least 7 mm, and preferably 10-12 mm, between the inflated balloon and the skin.