2924 - Safety and Efficacy of Pencil Beam Scanning Proton Therapy for Curative-Intent Reirradiation of Recurrent Breast Cancer
Presenter(s)
M. A. Chakraborty1, A. J. Khan2, O. Cahlon3, A. Lozano4, S. Desai4, L. Z. Braunstein2, D. A. Roth O’Brien2, Q. LaPlant2, B. McCormick2, S. N. Powell2, and I. J. Choi2,5; 1Rutgers New Jersey Medical School, Newark, NJ, 2Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY, 3New York University Grossman School of Medicine, Department of Radiation Oncology, New York, NY, 4Center for Biostatistics and Health Data Science, Department of Statistics, Virginia Tech, Roanoke, VA, 5New York Proton Center, New York, NY
Purpose/Objective(s): Despite a need for improved local-regional control (LRC) after salvage surgery alone, reirradiation (reRT) has been delivered infrequently for breast cancer recurrences due to concerns for excess severe toxicities from high cumulative dose to organs-at-risk. Proton therapy (PBT) may be the preferred radiation therapy (RT) modality for reRT given superior avoidance of non-target tissues previously exposed to RT. We hypothesize that pencil beam scanning proton therapy (PBS-PBT) reRT for breast cancer recurrence provides excellent LRC with acceptable rates of high-grade toxicities.
Materials/Methods: Patients treated with curative-intent pencil beam scanning proton therapy (PBS-PBT) reRT for recurrent breast cancer and with dose overlap from prior RT were identified. Patient and tumor characteristics, treatment parameters, and clinical outcomes were collected. Time to recurrence was defined from reRT completion to event. Fisher’s exact and non-parametric comparison tests were used to assess correlations between clinical outcomes and salient clinicopathologic and treatment characteristics. RT doses represent a proton RBE correction factor of 1.1.
Results: In total, 63 consecutive patients met study criteria. Median age was 63 years (range, 35-87). At reRT, 51% had pN+ disease, 29% lymphovascular invasion, 27% dermal invasion, 24% extracapsular extension, 14% nipple/stroma invasion, and 13% skeletal muscle invasion. Median time between RT courses was 93.8 months (11.7-393.2). Median initial (C1), reRT (C2), and total RT doses were 52.6 Gy, 50.4 Gy and 109.9 Gy, respectively. For C1, 64% received whole breast (WB)/chest wall (CW) RT, 22% WB/CW + regional nodal irradiation (RNI), 3% partial breast irradiation (PBI), and 2% intraoperative RT (IORT). For C2, 81% received WB/CW + RNI, 10% PBI, 6% partial LN/RNI only, and 3% other partial fields. At a median follow-up of 22.2 months (0.9-59.1), there were 3 (5%) local recurrences, 1 (2%) regional recurrence, 6 (10%) distant recurrences, and 1 (2%) death. Dermal invasion (p=0.02) and positive surgical margin (p=0.01) were associated with recurrence risk. Max acute AE grade (G) was G2 in 51% of patients and G3 in 3% (RT dermatitis, n=1; skin pain, n=1). Max late AE was G2 in 35% and G3 in 6% (shoulder stiffness, n=3; wound complication, n=1; fibrosis, n=1; arm lymphedema, n=1; breast/CW lymphedema, n=1). There were no G4/5 AEs. Rib fracture occurred in 11%. Higher reRT dose was associated with acute G2+ AE (p=0.024).
Conclusion: To our knowledge, this is the largest single institution study of patients receiving PBT reRT for breast cancer recurrence to date. Despite the predominantly high-risk nature of our cohort, PBT reRT resulted in excellent rates of LRC and limited high-grade AEs, demonstrating the promise of this approach. Continued investigation will be needed to optimize salvage treatment approaches and provide increased clarity on the clinical impact of reRT for breast cancer recurrence.