M. J. Case1, E. Gelover1, M. Zhu1, K. M. Langen1, M. W. McDonald2, S. T. Kahn1, and S. W. Dutta1; 1Department of Radiation Oncology, Emory University, Atlanta, GA, 2Emory Proton Therapy Center, Atlanta, GA
Purpose/Objective(s): To evaluate clinical characteristics and symptoms in patients with lung changes following intensity modulated proton therapy (IMPT) for breast cancer. Materials/
Methods: From a cohort of 107 patients treated with IMPT for breast cancer from 7/2019 – 12/2022, 45 patients were retrospectively identified with subsequent CT lung imaging changes during follow-up appointments. Ipsilateral lung constraint was typically V20Gy < 20%. Treatment details including type of surgery and utilization of chemotherapy, patient reported respiratory symptoms, development of rib fractures, and treatment planning details were abstracted. The areas of lung density changes on follow-up imaging were contoured to quantify volume of change. CTCAE V5 pneumonitis scoring was assigned at any point after completion of IMPT. Results: Among the 45 patients, the average volume of post-radiation lung changes was 34 cc (range 0.7 cc – 144 cc). Most patients had been treated to 50 Gy in 25 fractions (42/45, 93%), with comprehensive nodal irradiation (41/45, 91%), and with a boost to cavity and/or nodal regions (25/45, 56%). Several patients (11/45, 24%) had received prior breast radiation. Most patients (33/45, 73%), were treated in the post-mastectomy setting with 11/45 (24%) patients having permanent implants, 6/45 (13%) having tissue expanders, 3/45 (7%) having a remote historical flap, and 13/45 (29%) having no reconstruction. Most patients had also received chemotherapy at some point in treatment (39/45, 87%). Using CTCAE V5 pneumonitis scoring, grade 1 (asymptomatic) was noted in 27/45 (60%) of patients, grade 2 (symptomatic, not limiting self-care or requiring oxygen) in 15/45 (33%), and grade 3 or higher (self-limiting or requiring oxygen) in 3/45 (7%). A proportion of patients (9/45, 20%) also developed rib fractures. The average time to develop rib fractures was 20 months (range 7- 41 months). Conclusion: Post-mastectomy patients with radiologic lung changes are at risk for symptomatic pneumonitis and rib fracture following IMPT. Additional lung and chest wall objectives specific to proton therapy for breast cancer are warranted.
