Clinical Outcomes and Institutional Experience of Ultrahypofractionated Radiation Therapy in Patients With Breast Cancer.

Purpose: Prompted by COVID-19 and publication of the FAST-Forward study, our institution rapidly implemented ultrahypofractionated radiation therapy (U-HFRT) for patients with early-stage breast cancer. Our objective was to evaluate our early experience and toxicity outcomes for U-HFRT. Methods and Materials: Patients with consecutive stage 0-II breast cancer treated with adjuvant whole breast radiation therapy (RT) were evaluated. Patient demographics and treatment characteristics were extracted and categorized into 2 cohorts: U-HFRT, 26 Gy/5 fractions (F) and M (moderate)-HFRT, 40.05 Gy/15F. Physician-assessed skin toxicity was evaluated using the Radiation Therapy Oncology Group radiation morbidity scale at baseline/during RT, 1 to 90 days post-RT and >90 days post-RT. Descriptive statistics summarized patient demographics and treatment characteristics and were stratified based on dose fractionation. A multivariable logistic model evaluated associations between toxicity and fractionation. Results: Between May 2020 and March 2021, 320 patients were evaluated: 133 (41.6%) received U-HFRT and 187 (58.4%) received M-HFRT. For the U-HFRT cohort, median age at diagnosis was 65.4 years (range, 57-73), 71% had hormone receptor-positive invasive disease, and 18% had ductal carcinoma in-situ. All patients received whole breast RT, and 33% received a boost. U-HFRT was used more in patients who were older, hormone receptor-positive, and did not receive a boost ( Conclusions: This study reports real-world clinical outcomes of patients with stage 0-II breast cancer treated with U-HFRT. We observed low rates of acute skin toxicity compared to M-HFRT, confirming its acceptability as a standard regimen for select patients. Longer term follow-up would be necessary to confirm clinical outcomes in terms of both local control and late normal tissue toxicity.