Abstract P1-10-03: Ultra-hypofractionated Radiotherapy for Breast Cancer: A Brazilian Single-Institutional Series

Abstract

Abstract INTRODUCTION Extreme hypofractionation in patients with early-stage breast cancer has been studied in randomized phase III non-inferiority trials. There is scarce data on this strategy in Latin American patients. OBJECTIVES To describe the profile of patients diagnosed with breast cancer treated with radiotherapy with an ultra-hypofractionated regimen (5 fractions of 5.2 Gy, in one week), as well as the dosimetric aspects and acute toxicity related to the treatment. METHOD Retrospective cohort through a Brazilian uni-institutional series, with analysis of pathological, dosimetric, and toxicity variables. RESULTS Between May 2020 and March 2022, 67 patients were included, with a median age at diagnosis of 71 years (41-93). Regarding staging, 25.8% had in situ tumors, 60.6% of patients were IA, and only 3% were stage IIA. Nineteen percent of patients had histological grade 3; 24.6%, had nuclear grade 3. Hormone receptors were positive in 92.1% of patients. The mean ki67 was 19%, and HER2 was negative at 84.5%. All patients underwent conservative surgery, and 5 underwent reconstruction with autologous flaps. Fifty-one patients underwent hormone therapy and only 2 underwent adjuvant chemotherapy. All but two patients were treated with the conformal technique (VMAT was used due to unfavorable anatomy). The mean volume of the irradiated breast was 926 cm3 (ranging from 920 to 932 cm3). Regarding the constraints of the organs at risk, the average V8Gy of the ipsilateral lung was 11.4%, ranging from 0 to 24%. In the heart, the average volumes receiving 1.5Gy and 7Gy were, respectively, 9.2% and 0.7%. No patient had acute toxicity greater than grade 2. The effects on the skin appeared on average 20 days after the end of treatment, with resolution in a maximum of 3 months. The median follow-up time was 10 months (3 - 26). We did not observe any case of local-recurrence, of breast-cancer-related death. CONCLUSION Although our follow-up time is premature, we have found that ultra-hypofractionated radiotherapy was feasible, tolerable, and safe, for patients with early breast cancer. Also, the constraints on the organs at risk were respected. There were no high-grade acute toxicities. Besides convenience, ultra-hypofractionation can improve access to radiotherapy in resource-scarce settings. Citation Format: Leticia Hernandes de Brito, Felipe Cicci Farinha Restini, Maria Thereza Mansur Starling, Gabriela Silva Moreira de Siqueira, Gustavo Nader Marta, Heloisa de Andrade Carvalho, Samir Abdallah Hanna. Ultra-hypofractionated Radiotherapy for Breast Cancer: A Brazilian Single-Institutional Series [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-10-03.