2908 - Radiation-Induced Brachial Plexopathy after Proton Reirradiation for Breast Cancer
Presenter(s)
I. J. Choi1,2, A. Abbasi3, O. Cahlon4, L. Z. Braunstein1, D. A. Roth O’Brien1, B. McCormick1, A. J. Khan1, and S. N. Powell1; 1Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY, 2New York Proton Center, New York, NY, 3Lewis Katz School of Medicine at Temple University, Philadelphia, PA, 4New York University Grossman School of Medicine, Department of Radiation Oncology, New York, NY
Purpose/Objective(s): In the setting of prior radiotherapy (RT) to overlapping treatment volumes, regional nodal irradiation for breast cancer can result in cumulative dose to the brachial plexus (BP) far exceeding established dose constraints. Radiation-induced brachial plexopathy (RIBP) is a morbid RT sequela that can profoundly impact quality of life. The cumulative BP dose constraint for breast reirradiation (reRT) has not been established. Proton therapy (PBT) has been previously demonstrated to achieve optimal BP sparing with minimal target coverage loss. We hypothesize that PBT reRT using internally-developed planning guidelines and dose constraints results in low rates of RIBP and excellent locoregional disease control.
Materials/Methods: Patients treated with PBT reRT for breast cancer with BP overlap with the prior RT course were identified. Clinicopathologic features, RT details, and clinical outcomes were collected. Relevant outcomes were correlated with patient, tumor, and treatment characteristics. An institutional cumulative BP (BPsum) max dose constraint of <85Gy (RBE) was applied when clinically appropriate. PBT doses represent an RBE correction factor of 1.1.
Results: In total, 22 consecutive patients were identified. Median age was 60 years (37-82); treatment intent was curative in 77%. Most patients (82%) received prior RT for breast cancer; the remainder were previously treated for Hodgkin’s lymphoma. Median time between RT courses was 99 months (12-276). Median 1st course, reRT, and plan sum cumulative doses were 50.4 Gy (22.5-61; 50Gy2, a/ß=3, 19.8-69.2), 50.4 Gy (RBE) (41.4-66.4; 49 Gy2, a/ß=3, 39.7-62.4), and 103.9 Gy (RBE) (72.9-124.8; 103.7 Gy2 (RBE), a/ß=3, 68.2-122.4), respectively. Median max and mean BP reRT doses were 36.7 Gy (RBE) (17.1-53.9) and 24.8 Gy (RBE) (6-48), respectively; median BPsum max and mean doses were 83.1 Gy (RBE) (54.7-101.6) and 61.9 Gy (RBE) (40.8-80.1), respectively. BPsum max dose <85Gy (RBE) was achieved in 18/22 patients. At a median follow-up of 21 months (0.5-49), RIBP developed in 9% (n=2), with both events occurring with a BPsum max >85Gy (RBE). BPsum max dose >85 Gy (RBE) was significantly associated with increased RIBP risk (50% vs. 0%, p<0.001). Both cases of RIBP were grade 1 (neuropathy in the ulnar nerve distribution not requiring intervention) and developed 8 months post-reRT. RIBP persisted for 41 months with a BPsum max of 101.6 Gy (RBE) but resolved after 16 months with a BPsum max of 94.7 Gy (RBE). No disease recurrences occurred in curative intent patients.
Conclusion: PBT reRT applying a BPsum max dose of <85 Gy (RBE) results in no RIBP events and excellent disease control. Longer follow-up and further experience incorporating other potentially influencing factors such as tissue recovery between courses, dose-volume relationship, and other treatment-related and clinicopathologic features are needed to support these findings and establish a standard BP dose constraint in the reRT setting.