Toxicity and Cosmetic Outcomes after Proton-Based Radiotherapy Following Breast-Conserving Surgery

Proton-based radiotherapy is being used more frequently as proton centers are expanding across the country. Various studies are currently comparing cardiovascular and efficacy outcomes between proton-based versus photon-based radiotherapies, but toxicity and cosmetic outcomes remain unknown. A recent retrospective review analyzed dosimetric data, early toxicity, and patient-reported cosmetic outcomes in patients with breast cancer who underwent adjuvant proton-based radiotherapy following breast-conserving surgery. The findings were reported in a poster presentation at the San Antonio Breast Cancer Symposium.

The researchers reviewed their institutional database for information on patients with breast cancer who underwent breast-conserving therapy prior to proton-based radiotherapy between 2015 and 2019. Patient-reported cosmetic outcomes were analyzed and ranked as excellent, good, fair, or poor. The treating physician determined early toxicity outcomes per the National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE), version 3.0. Dosimetry data were collected using dose-volume histograms.

A total of 21 patients (median age, 58 years; range, 26-85 years; median body mass index, 26.1 kg/m2; range, 19.8-58.3 mg/k2) who received adjuvant proton-based radiotherapy were identified. Three patients each had a history of diabetes and smoking. Three patients previously underwent adjuvant radiotherapy for ipsilateral breast cancer, and one patient was treated with definitive radiotherapy for ipsilateral lung cancer. T1 primary tumors were present in 11 patients (52%), 15 (71%) were node-positive, and 12 (57%) had left-sided tumors. Neoadjuvant therapy was administered to 12 patients (57%), while five (24%) received adjuvant chemotherapy. In most patients (n=17, 81%), target volumes included the regional lymph nodes; 17 patients (81%) also underwent a lumpectomy boost (median dose, 10Gy; range, 10-14 Gy). The following median planning target volumes were reported: V95, 94%; V100, 71%; and V110, 2%. The median max point dose was 115%. The median ipsilateral breast V105 and V110 was 367.3 cc and 24.1 cc, respectively.

More than half of patients (62%) experienced CTCAE grade 2 dermatitis, and 14% experienced grade 3 dermatitis. One-third of patients reported grade 2 pain, and 10% reported grade 3 pain. Grade 2 fatigue presented in 33% of patients. There was one case of acute esophagitis. For cosmetic evaluation, patients were followed for a median 27 months; two patients died before evaluation. Most patients (n=15; 79%) reported good or excellent cosmetic outcome, and four (21%) reported fair cosmetic outcome. No patients reported a poor cosmetic outcome.