Breast neoplasm is the second most common type in the world. Radiation therapy is a key component in the treatment of breast cancer. Acute skin reaction is one of the most common side effects of radiation therapy. Several studies were performed for prophylaxis of this adverse event, however, until this moment there is no consensus for clinical practice . Second meta-analysis , the ideal candidate for the radiodermatitis prevention would be an agent capable of repairing damage to DNA or agents that promote cell proliferation . The low power laser promotes tissue repair ( reduces inflammatory phase and induces collagen synthesis ) . Its use in the treatment of adverse events of cancer treatment is well established in two situations : in the prophylaxis and treatment of mucositis and in the treatment of lymphedema . The purpose of this study is to use the low power laser in patients with breast cancer undergoing radiotherapy treatment to evaluate the effects of Laser InGaAIP 660Nm in preventing radiodermatitis.