Efficacy and Safety of Prepectoral Prosthesis Immediate One-Stage Breast Reconstruction Versus Two-Stage Expander/Prosthesis Reconstruction in Postoperative Adjuvant Radiotherapy Breast Cancer Patients: A Prospective, Single-Center, Cohort Study

Inclusion Criteria: 1. women aged 18 to 70； 2. Newly diagnosed breast cancer patients showing no evidence of distant metastasis on clinical examination and diagnostic workup； 3. adjuvant radiotherapy is required; 4. Patients scheduled to undergo nipple-sparing mastectomy (NSM) or skin-sparing mastectomy (SSM) with immediate prepectoral implant-based reconstruction (via open, endoscopic, or robotic approach) require adjuvant radiotherapy AFTER permanent implant placement; OR Patients scheduled for NSM/SSM with two-stage tissue expander/implant reconstruction (with expander placement in either submuscular or prepectoral plane) receive radiotherapy WITH the tissue expander in situ, followed by exchange for permanent implant ≥6 months post-radiotherapy (expander position: submuscular/prepectoral acceptable; surgical approach: open/endoscopic/robotic acceptable); 5. Patients are eligible regardless of whether mesh is used in the reconstruction surgery; 6. Patients with severe breast ptosis are eligible; 7. During the study observation period, lipofilling is permitted on the affected breast and symmetrization procedures on the contralateral breast in both cohorts; 8. ECOG performance status 0-1; 9. Patients receiving neoadjuvant chemotherapy (NACT) are eligible; 10. Bilateral breast reconstruction is permitted; 11. No smoking history OR smoking cessation ≥4 weeks prior to enrollment; 12. Investigator-confirmed protocol compliance capability; 13. Concurrent participation in other interventional/non-interventional trials is allowed if deemed non-interfering by the investigator; 14. Voluntarily participate and sign the informed consent form after comprehensive understanding. Exclusion Criteria: 1. Stage IV (metastatic) breast cancer; 2. No prior radiotherapy post-mastectomy; 3. History of ipsilateral chest wall/axillary radiation therapy; 4. Immunodeficiency, poorly controlled diabetes (HbA1c \>7%), or active tobacco use; 5. Inflammatory breast cancer (cT4d); 6. Autologous-based breast reconstruction or delayed reconstruction; 7. Severe cardiopulmonary/hepatic/renal comorbidities contraindicating surgery/radiotherapy (ASA class ≥III); 8. Psychiatric disorders precluding independent BREAST-Q completion; 9. Pregnancy or lactation; 10. Documented history of protocol non-adherence; 11. Life-limiting comorbidities interfering with treatment OR investigator-determined ineligibility.