Proton beam radiotherapy as part of comprehensive regional nodal irradiation for locally advanced breast cancer

Purpose This study evaluates acute toxicity outcomes in breast cancer patients treated with adjuvant proton beam therapy (PBT). Methods From 2011 to 2016, 91 patients (93 cancers) were treated with adjuvant PBT targeting the intact breast/chest wall and comprehensive regional nodes including the axilla, supraclavicular fossa, and internal mammary lymph nodes. Toxicity was recorded weekly during treatment, one month following treatment, and then every 6 months according to the Common Terminology Criteria for Adverse Events (CTCAE) v4.0. Charts were retrospectively reviewed to verify toxicities, patient parameters, disease and treatment characteristics, and disease-related outcomes. Results Median follow-up was 15.5 months. Median PBT dose was 50.4 Gray relative biological effectiveness (GyRBE), with subsequent boost as clinically indicated (N = 61, median 10 GyRBE). Chemotherapy, when administered, was given adjuvantly (N = 42) or neoadjuvantly (N = 46). Grades 1, 2, and 3 dermatitis occurred in 23%, 72%, and 5%, respectively. Eight percent required treatment breaks owing to dermatitis. Median time to resolution of dermatitis was 32 days. Grades 1, 2, and 3 esophagitis developed in 31%, 33%, and 0%, respectively. Conclusions PBT displays acceptable toxicity in the setting of comprehensive regional nodal irradiation.