Optical Surface Monitoring Technology-Guided Large-Segment Radiotherapy for Breast Cancer

Inclusion Criteria: 1. Patients who have undergone breast-conserving surgery or modified radical mastectomy for left breast cancer; 2. Planned whole-breast ± supraclavicular region, chest wall ± supraclavicular region radiotherapy; 3. Able to perform deep inspiration breath-hold technique with breath-holding time \>35s and can repeat it continuously for more than 6 times; 4. Patients who have not received neoadjuvant chemotherapy or breast reconstruction surgery; 5. No active heart disease, myocardial infarction, congestive heart failure or other cardiac diseases at baseline; 6. Patients are fully voluntary and able to sign the informed consent form 30 days before enrollment. Exclusion Criteria: 1. Bilateral breast cancer; 2. No pathological diagnosis; 3. Remote metastasis; 4. Receiving neoadjuvant chemotherapy or breast reconstruction; 5. Have received mediastinal radiotherapy in the past; 6. Previous history of abdominal or pelvic radiotherapy; 7. Previous or secondary primary malignant tumor; 8. Serious cardiac insufficiency; Myocardial infarction or uncorrected unstable arrhythmia or uncorrected unstable angina pectoris occurred in the last 3 months; Pericardial disease.