Prospective Study of Particle Radiotherapy for Breast Cancer With Different Arm Position

Inclusion Criteria: 1. Patients with pathologically (cytological or histological) confirmed breast cancer with positive lymph nodes and postoperative adjuvant radiotherapy 2. Exclude distant metastasis 3. No ipsilateral breast and breast radiation therapy 4. Exclude patients requiring axillary irradiation 5. Age 18-80 years old 6. General good health (Eastern Cooperative Oncology Group, ECOG 0-2) 7. No complications such as severe pulmonary hypertension, cardiovascular disease, peripheral vascular disease, or severe chronic heart disease that may affect radiotherapy. 8. Non-pregnant (confirmed by serum or urine β-HCG test) or lactating women 9. Patients must sign informed consent to receive radiotherapy. Exclusion Criteria: 1. Pathology unapproved breast cancer 2. With distant metastasis 3. The ipsilateral breast or breast has received radiation therapy 4. Patients requiring axillary irradiation 5. The dose limit of organs at risk cannot reach the preset safe dose limit 6. Pregnancy (confirmed by serum or urine β-HCG test) or lactation 7. Poor general health, Karnofsky Performance Status (KPS)\<70，or ECOG\>2 8. Severe complications that may affect radiotherapy, including: a) Unstable angina pectoris, congestive heart failure, myocardial infarction requiring hospitalization in the past 6 months, b) acute bacterial or systemic fungal infection, c) hospitalization for exacerbations of chronic obstructive pulmonary disease (COPD) or other respiratory diseases 9. Unable to understand the purpose of treatment or unwilling to sign the treatment consent