Early Institutional Experience of Ultra-Hypofractionated Breast Radiotherapy in a Large Academic Cancer Center

Abstract

<h3>Purpose/Objective(s)</h3> Ultra-hypofractionated radiotherapy (U-HFRT) is non-inferior to moderate hypofractionation (M-HFRT) for local control following breast-conserving surgery for early-stage breast cancer and is safe in terms of normal tissue toxicity. Our objective was to evaluate early institutional experience of U-HFRT in a real-world setting at a large academic cancer center. <h3>Materials/Methods</h3> Stage 0-II breast cancer patients who received adjuvant whole breast irradiation (WBI) or partial breast irradiation (PBI) between May 2020 and March 2021 were compiled. Patients were divided into 2 cohorts: U-HFRT (26 Gy in 5 daily fractions) and M-HFRT (40.05 Gy in 15 fractions). Clinical and treatment characteristics were extracted from medical records and displayed using descriptive statistics. Physician-assessed skin toxicity was collected for patients treated with U-HFRT during RT and at follow-up visits using the RTOG radiation morbidity scale. Associations between toxicity and clinical/treatment characteristics were determined using mixed effects logistic regression, accounting for time. Comparisons between the U-HFRT and M-HFRT cohorts were performed using the Wilcoxon rank sum test (continuous) and Chi-square/Fisher's exact test (categorical). <h3>Results</h3> Median age at diagnosis for the entire cohort was 60.5 years: U-HFRT 66.2 years and M-HFRT 55.1 years (p<0.001). For the U-HFRT cohort, 70% had hormone-receptor positive invasive breast cancer (70% pT1c, 95% pN0) and 20% had DCIS. WBI/PBI was delivered to 385 patients, of which 188 (49%) received U-HFRT. For these patients, the majority (72%) received WBI, 28% PBI and a boost was used in 26%, compared to 96%, 4% and 47%, respectively, for those treated with M-HFRT (p<0.001). Grade 1 RTOG skin toxicity significantly improved over time for patients who received U-HFRT: 37% during RT, 57% within 90 days post-RT and 6% >1-year post-RT (p<0.001). Grade 2 toxicity was minimal (5% within 90 days post-RT) and there were no grade 3 toxicities. Age, RT volume (WBI vs. PBI) and chemotherapy were not associated with toxicity for U-HFRT; however, increased toxicity was observed for patients who received a boost (p<0.001). Factors associated with increased usage of U-HFRT were older age, use of PBI, no boost and no breast reconstruction (p<0.001). <h3>Conclusion</h3> U-HFRT was rapidly adopted at our institution for early-stage breast cancer and is associated with low rates of reported skin toxicity. The use of U-HFRT was greatest in patients with low-risk breast cancer, consistent with a conservative approach to implementation in a real-world setting.