Verification of Range Accuracy and Correlation With Clinical Toxicity Using Offline PET/CT for Hypofractionated Proton Radiotherapy in Breast Cancer

This is a single-arm, single-center, prospective observational study. It uses offline PET/CT to verify and quantify the range accuracy of hypofractionated proton radiotherapy for postoperative breast cancer. The correlation between range error and clinical toxicities (radiation pneumonitis, rib fracture) will be analyzed. A PET signal-proton range correlation model will be established using Monte Carlo simulation to provide evidence for optimizing proton therapy planning.

Inclusion Criteria: 1. Written informed consent obtained. 2. Female aged ≥18 years. 3. Pathologically confirmed breast cancer after curative surgery (breast-conserving or mastectomy) and indicated for postoperative adjuvant radiotherapy. 4. Scheduled to receive moderate or ultra-hypofractionated proton therapy. 5. KPS ≥80, expected survival \>5 years. 6. Well-healed surgical incision without infection. 7. Fertile females must use contraception for ≥1 month before screening and throughout the study. Exclusion Criteria: 1. Pregnant or lactating female. 2. Severe non-neoplastic medical comorbidities precluding radiotherapy. 3. Inability to cooperate or comply with offline PET/CT examination.