Evaluation of Acute and Subacute Side Effects among Different Fractionation Schemes of Adjuvant Radiotherapy in Patients with Breast Cancer

Abstract Breast cancer (BC) is the most prevalent malignancy among women in Brazil. Radiotherapy (RT) stands out for its importance as adjuvant treatment and can be classified according to fractionation as conventional (CFRT), moderately hypofractionated (MHFRT), and ultra-hypofractionated (UHFRT). A lower number of fractions is associated with a lower toxicity. This study evaluated the prevalence of acute and subacute side effects among BC patients undergoing different RT fractionations. This is a Brazilian retrospective cohort study conducted at a state reference center for RT from January 2020 to June 2023. Descriptive and bivariate analyses were performed based on data collected from physical records of 718 patients. The prevalence of side effects in different fractionations of RT treatment was 91.9% in CFRT, 85.9% in MHFRT, and 44.4% in UHFRT (95% CI, p < 0.001). Radiodermatitis was the most evident side effect, regardless of the fractionation adopted, with G1 and G2 grades being the most common. In this study conducted at an institution in Brazil, MHFRT and UHFRT showed a lower prevalence of side effects, endorsing the encouragement for the consolidation of RT in fewer fractions as adjuvant treatment for BC.