Radiotherapy is one of the important treatments to improve the survival rate of breast cancer patients, but also has the risk of radiation lung injury, which can develop into pulmonary fibrosis. Hyperbaric oxygen can improve the tissue after radiation by promoting the function of vascular endothelial cells and fibroblasts, and reducing the secretion of inflammatory factors, thereby inhibiting the process of fibrosis and fiber atrophy after radiotherapy, and promoting tissue repair. Therefore, it has the potential value of treating chronic radiation injury. We aim to investigate whether hyperbaric oxygen treatment can reduce the incidence of radiation pneumonia and improve patients' quality of life, and to evaluate its safety and the impact on the patients' long-term survival outcomes.

Radiotherapy is one of the important treatments to improve the survival rate of breast cancer patients. Radiotherapy also has the risk of radiation lung injury, which can develop into pulmonary fibrosis, which seriously affects the quality of life of patients. Hyperbaric oxygen has received more attention in the field of delayed tissue damage caused by radiotherapy. In a hyperbaric oxygen environment, sufficient oxygen supply can improve the tissue after radiation by promoting the function of vascular endothelial cells and fibroblasts, and reducing the secretion of inflammatory factors. Low blood vessel density, low cell activity and low oxygen content in the "three low" state, thereby inhibiting the process of fibrosis and fiber atrophy after radiotherapy, and promoting tissue repair. Therefore, it has the potential value of treating chronic radiation injury. Can hyperbaric oxygen therapy be applied for breast cancer patients who were receiving radiotherapy, reduce the risk of radiation pneumonitis, prevent radiation pneumonitis and even radiofibrosis, and improve long-term survival? Therefore, we plan to prospectively enroll 380 breast cancer patients and randomly divide them into two groups. The treatment group will be given 30-40 hyperbaric oxygen therapy immediately after the end of radiotherapy, to study whether hyperbaric oxygen therapy reduces the risk of radiation pneumonia, and to evaluate hyperbaric oxygen The safety of treatment and its impact on the patient's quality of life and long-term survival outcomes provide an effective means to reduce the incidence of radiation pneumonia and improve the long-term quality of life.

Inclusion Criteria:

• (1) Volunteer to participate and sign informed consent in writing. (2) Past pathological diagnosis of breast cancer followed by radical treatment/surgery for breast cancer, followed by adjuvant chemotherapy followed by radiotherapy.

  (3) Excluding patients with simple neck lymph node recurrence and patients with distant metastases.

  (4) There is no secondary malignant tumor in other parts. (5) Age at entry ≥ 18 years old and ≤ 70 years old, both male and female. (6) The Eastern Cooperative Oncology Group (ECOG) has a performance status score of 0 or 1.

  (7) The expected survival period is ≥2 years. (8) There was no acute radiation lung injury in chest CT examination before and after radiotherapy

Exclusion Criteria:

• (1) Contraindications to hyperbaric oxygen therapy: lung disease (severe chronic obstructive airway disease, bullous lung disease, acute or chronic lung infection, uncontrolled asthma, untreated pneumothorax), in the past History of ear surgery, middle ear disease (eustachian tube dysfunction, recurrent dizziness), eye disease (retinal detachment).

  (2) Have received hyperbaric oxygen therapy in the past. (3) Radiation pneumonia had occurred at the time of enrollment or before receiving hyperbaric oxygen therapy.

  (4) Women who are pregnant or breastfeeding. (5) Patients who have not completed comprehensive breast cancer treatment due to disease progression, intolerable side effects, abandonment of treatment and other reasons.

  (8) Patients who need mechanical ventilation support. (9) Patients who cannot follow and understand simple commands. (10) Patients with disorientation and mental disorders.

there is no plan to make individual participant data (IPD) available to other researchers.