<b>Study of Acute and Late Side Effects in Breast Cancer Patients Treated with Ultra-Hypo-Fractionated Radiation Therapy</b>

Background: Breast cancer imposes a substantial clinical burden in Pakistan, and shorter radiotherapy schedules may improve patient convenience and optimize limited oncology resources. Ultra-hypofractionated breast radiotherapy has gained increasing acceptance internationally, but local real-world toxicity data remain limited. Objective: To evaluate the acute and late side effects of ultra-hypofractionated adjuvant breast radiotherapy in patients with breast cancer treated at a tertiary cancer center in Pakistan. Methods: This retrospective observational study included 86 adult female patients with node-negative breast cancer treated between January 2021 and December 2022 with 26 Gy in 5 fractions, with or without a boost of 10 Gy in 5 fractions. Toxicities were assessed using Common Terminology Criteria for Adverse Events version 5 at the end of treatment, 4, 8, and 12 weeks, and at 6 and 12 months. Results: The mean age was 43.8 years. Most patients received field-in-field radiotherapy (82.6%). Radiation dermatitis was the most frequent acute toxicity, with 59.3% Grade 0, 38.4% Grade 1, and 2.3% Grade 2 events; no Grade 3-4 dermatitis occurred. Radiation pneumonitis was observed in 4.7%, acute lymphedema in 2.3%, and skin hyperpigmentation in 2.3%, all of low grade. Among 57 patients with long-term follow-up, breast fibrosis occurred in 14.0% and late lymphedema in 3.5%. Conclusion: Ultra-hypofractionated breast radiotherapy showed an overall favorable and clinically manageable toxicity profile in this cohort, supporting its practical use in routine care, although larger prospective comparative studies are needed.