Cosmetic Outcomes and Toxicity in Patients Treated With Proton Therapy After Breast Conserving Surgery

Abstract

There has been reluctance to treat post-lumpectomy patients with proton therapy due to potential skin toxicity and setup uncertainty. Here we report skin toxicity, cosmesis, and treatment efficacy/reproducibility in a cohort of breast cancer patients treated with lumpectomy followed by postoperative proton radiation therapy to the intact breast. 26 patients treated with lumpectomy followed by proton therapy with at least 6 months of follow up were analyzed. Six (23.1%) had stage III disease, 13 (50%) stage II, 5 (19.2%) stage I and 2 (7.7%) DCIS. Fifteen patients (57.7%) were treated to the breast and regional nodes (with internal mammary node coverage in 93.3%) and 42.3% were treated to the breast alone. Seven (26.9%) had an axillary dissection. Proton therapy was delivered with uniform scanning beams using 2-4 en face fields per day with a daily feathered match. The median dose to the initial volume was 48.6 Gy (RBE) (range 45 – 52), and the lumpectomy cavity was boosted to a median of 60.6 Gy (RBE) (48.7 – 65). Patients were seen and photographed weekly while on treatment, 1 month after RT completion and, in general, every 6 months thereafter. Toxicity was assessed using CTCAE v4.0. Cosmesis was retrospectively assessed via photographs and validated among 3 blinded practitioners using the Harvard 4-point breast cosmesis scale. Based on clinical assessment of edema during treatment, and verification CT scans as needed, no patients required adaptive re-planning. With a median follow up of 15 months, the 2-year local failure free survival is 95.8%, regional failure free survival 89.4%, and distant failure free survival 96.2%. Locoregional failures included a Stage II patient that experienced a combined breast and axillary recurrence 9 months after therapy, and a stage III patient with known supraclavicular lymph node involvement who progressed in the SCV 14 months after completion of RT to the breast and nodes. There were no Grade 3 adverse early or late events. The incidence of acute Grade 2 dermatitis was 46.2% (n=12). Six (23.1%) developed moist desquamation. The rate of late Grade 1 hyperpigmentation, telangiectasia, and fibrosis was 46.2% (n=12), 3.8% (n=1), and 11.5% (n=3) respectively. One patient (3.8%) developed Grade 2 fibrosis. There have been no cases of pneumonitis, cardiac toxicity, or rib fractures. 88.4% of patients had an excellent or good cosmetic outcome and 11.5% experienced a fair cosmetic outcome. There were no cases of poor cosmesis. Locoregional control with postoperative proton therapy after lumpectomy was excellent and does not seem compromised due to reproducibility/setup issues. Due to the higher skin dose with uniform scanning protons, the rate of moist desquamation was slightly higher than historical series of photons; however, late skin toxicity and fibrosis was minimal and 88% of patients had excellent/good cosmesis. Further follow up is planned to assess for long-term outcomes and toxicity.