Abstract P4-12-20: Early toxicity and patient-reported cosmetic outcomes in patients treated with adjuvant proton-based radiotherapy after breast-conserving surgery

Background: As the number of proton centers continues to increase nationwide, the use of proton-based radiotherapy (RT) in the treatment of malignancies is expanding. Randomized trials to assess the efficacy and cardiovascular benefits of proton-based RT compared to photon-based RT in the treatment of breast cancer are underway. However, the data on early toxicity and cosmetic outcomes remains limited. In this study, we report dosimetric data, early toxicity, and patient-reported cosmetic outcomes in breast cancer patients treated with adjuvant proton-based RT after breast-conserving surgery. Methods: We performed a retrospective review of our institutional database to identify breast cancer patients treated with breast-conserving surgery followed by proton-based RT from 2015 to 2019. Patient-reported cosmetic outcomes were graded as excellent, good, fair, and poor. Early toxicity outcomes were graded by the treating physician during the treatment course using the National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE), version 3.0. Dose-volume histograms (DVHs) were reviewed to obtain dosimetry data. Results: We identified 21 patients treated with adjuvant proton-based RT. Median age at diagnosis was 58 (range, 26-85). Median body mass index was 26.1 (range, 19.8-58.3). Three patients (14%) had a history of diabetes and three patients (14%) smoking. Three patients (14%) had a history of ipsilateral breast cancer treated with adjuvant RT, and one patient had a history of ipsilateral lung cancer treated with definitive RT. Eleven patients had T1 primary tumors (52%), fifteen (71%) were node-positive, and twelve (57%) had left-sided tumors. Twelve patients (57%) received neoadjuvant and five patients (24%) adjuvant chemotherapy. Median whole breast dose delivered was 46.8Gy (range, 40.0-50.4Gy). Target volumes included the regional lymph nodes in seventeen patients (81%). Seventeen patients (81%) received a lumpectomy boost with a median dose of 10Gy (range, 10-14Gy). The median planning target volume V95 was 94% (range, 77-100%), V100 71% (range, 60-97%), V110 2% (range 0-18%), and median max point dose was 115% (range, 105-120%). The median ipsilateral breast V105 was 367.3cc (range, 0-1172cc) and V110 was 24.1cc (range, 0-321.3cc). Median mean heart dose was 0.39Gy (range, 0-2.6Gy). Median ipsilateral lung V20 was 10% (range, 0-28%) and ipsilateral lung V5 was 28.5% (range, 0.8-55.7%). CTCAE grade 2 dermatitis occurred in 62% and grade 3 in 14% of patients. Grade 2 pain was reported by 33% and grade 3 by 10% of patients. Grade 2 fatigue was reported by 33% of patients. One patient developed acute esophagitis. Median follow-up at the time of cosmetic evaluation was 27 months (range, 5-42 months). Two patients died before cosmetic evaluation. Four patients (21%) reported fair cosmetic outcome and 15 patients (79%) reported good or excellent cosmetic outcome. No poor cosmesis was reported. Conclusions: Adjuvant proton-based radiotherapy after breast-conserving surgery results in low normal tissue exposure compared to typical photon-based plans, particularly when the regional lymphatics are targeted. Proton-based RT is well tolerated with acceptable rates of acute toxicities and a high rate of good-to-excellent patient-reported cosmetic outcomes. Citation Format: Mutlay Sayan, Yin Zhang, Bo Liu, Apar Gupta, Bruce Haffty, Nisha Ohri. Early toxicity and patient-reported cosmetic outcomes in patients treated with adjuvant proton-based radiotherapy after breast-conserving surgery [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-12-20.