Presenter(s)
E. Braschi Jordan1, N. P. Mendenhall1, T. Burchianti2, C. G. Morris1, and J. A. Bradley1; 1Department of Radiation Oncology, University of Florida College of Medicine, Jacksonville, FL, 2University of Florida Health Proton Therapy Institute, Jacksonville, FL
Purpose/Objective(s): To evaluate outcomes in patients with breast cancer treated with proton therapy including regional nodal irradiation (RNI) with the hypothesis that proton therapy for RNI is associated with favorable disease-control outcomes and acceptable toxicity profiles.
Materials/Methods: Patients with breast cancer treated with adjuvant proton therapy including RNI between 2017 and 2023 were identified from a prospective registry. RNI targeted axillary, supraclavicular, and internal mammary nodes (IMN). Patients treated solely to the low axilla or IMN, with recurrent or metastatic disease, synchronous malignancies, or requiring reirradiation were excluded. Disease-control outcomes were estimated using Kaplan-Meier analysis.
Results: A total of 239 patients (243 breasts including four patients treated biliaterally) were included. Median age was 56 years (range, 25-84) and median follow-up was 3.7 years (range, 0.3 – 8.3); among living patients (n=197), median follow-up was 4.1 years. Most tumors (65%) were clinical stage II-III. Laterality was left-sided in 64%, right-sided in 31%, and bilateral in 5%. Systemic therapy included neoadjuvant (60%), concurrent (44%), and adjuvant (82%) treatment; 23% achieved pathologic complete response after neoadjuvant chemotherapy. Breast-conserving surgery was performed in 40% and mastectomy in 60%. Axillary surgery included sentinel lymph node biopsy alone (55%), axillary lymph node dissection (24%), or both (21%). Median initial dose was 50 GyRBE (range, 40.05-53), and 73% received a boost (92% tumor bed/incision; 39% nodal) with a median boost dose of 10 GyRBE (range, 6-20). Five-year overall survival was 83% [95% Confidence Interval (CI): 77-87%], locoregional control was 99% (95% CI: 96-100%), cause-specific survival was 87% (95% CI: 82-92%), and freedom from distant metastases was 78% (95% CI: 71-83%). Late grade 3 toxicities included cellulitis (2.9%) and deep fibrosis (2.5%). Late grade <2 toxicities included rib fracture(s) (7.4%) and radiation pneumonitis (2%).
Conclusion: While randomized trials comparing photon and proton therapy for patients with breast cancer requiring RNI are ongoing, our institutional cohort demonstrates durable disease control with low toxicity using proton therapy. These findings support the continued use of proton therapy for RNI.