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.

This study will be a prospective double- blind trial. Patients with breast cancer with stages I-III undergoing to radiotherapy will be included. The participants will be allocated into an intervention group (laser therapy in 26 patients) or a control group ( in 26 patients the laser will be disabled without affecting its apparent function) , five days a week before radiotherapy . The low level laser therapy used in this trial will be Photon Lase III (DMC, approved by ANVISA for medicinal purposes). This InGaAIP laser emits a pulsed 660 nanometer beam with an average output of 80 milliwatts and the average energy density delivered to the breast will be 3 J/cm2. Skin reactions will be graded weekly by a nurse, by a radiotherapist and by an oncologist using the common toxicity criteria (CTC -developed by the National Cancer Institute ) and Acute Radiation Morbidity Scoring Criteria (developed by Radiation Therapy Oncology Group). The patients will answer the modified visual analogue scale for pain (patient self-evaluation).

Inclusion Criteria:

1. Age at least 18 years, female gender only.

2. Patients with histological diagnosis of breast cancer (invasive ductal carcinoma, invasive lobular and other types), stages I-III

3. Patients who underwent breast-conserving surgery or mastectomy without breast reconstruction

4. Patients undergoing to adjuvant radiotherapy with conventional dose according to Barretos Cancer's Hospital protocol

5. Patients in the radiotherapy planning , presenting :

   • In the central court : " Hot Spot " ( ICRU ) ≤ 107 %
   • At full volume : " Hot Spot " ( ICRU ) ≤ 110 %

Exclusion Criteria:

• Patients undergoing mastectomy with immediate breast reconstruction
• Patients without histological diagnosis of breast cancer
• Patients with indication for radiotherapy without conventional dose
• Patient with indication for treatment in supraclavicular fossa
• Patients suffering from collagen
• Patients who do not meet the criteria for planning radiotherapy