S250
Clinical - Breast
ESTRO 2026
Annick Van Greveling 2 , Giselle Post 2 , Lorraine Donnay 4 , Monique Seret 4 , Dominique De Bal 5 , melissa Thomas 5 , Leen Geuens 5 , Werner De Gersem 1,2 , Vincent Remouchamps 4 , Alex De Caluwé 5,6 1 Human Structure and Repair, Ghent University, Ghent, Belgium. 2 Radiation Oncology, Ghent University Hospital, Ghent, Belgium. 3 Radiotherapy, University Medical Center Groningen, Groningen, Netherlands. 4 Radiation Oncology, CHU UCL Namur, site Sainte Elisabeth, Namur, Belgium. 5 Radiation Oncology, AZ- Sint Maarten, Mechelen, Belgium. 6 Radiation Oncology, Institut Jules Bordet, Hôpital Universitaire de Bruxelles (HUB), Université Libre de Bruxelles (ULB), Bruxelles, Belgium Purpose/Objective: Following our feasibility trial and acute toxicity analysis, the YO-HAI5 trial (Young-Old Highly Accelerated Irradiation in 5 Fractions) evaluates a 5- fraction schedule for whole-breast irradiation (WBI), including a simultaneously integrated boost (SIB)1,2. Radiation-related side-effects (RRSE) and disease outcomes at two-years follow-up are presented. Material/Methods: YO-HAI5 is a multicentre, phase 3, randomised, non- inferiority trial performed at three radiotherapy centres in Belgium. Patients referred for adjuvant WBI after breast-conserving surgery were randomly allocated to 15 fractions of 2.67 Gy in 3 weeks to the breast and lymph nodes if indicated (SIB, 15 x 3.12 Gy) or 5 fractions of 5.7 Gy in 12 days (SIB, of 5 x 6.2 Gy; LNI, 5 x 5.4 Gy). The primary endpoint was breast retraction 2 years after radiotherapy assessed from photographs. Assuming a 27% 2-year incidence for 40.05 Gy, non-inferiority was predefined as ≤ 10% excess for the 5-fraction schedule. Secondary endpoints were RRSE. Trial registration: NCT03677427. Results: 488 women were enrolled between 2017 and 2023 and only two-year photographs were available for 303 patients (62%) due to COVID-19 restrictions. For 405 patients (83%), two-years follow-up data for RRSE were available. Patient and treatment characteristics are shown in Figure 1. Breast retraction was observed in 79 patients (15-fractions, 37 (24.7%); 5-fractions, 40 (27.6%)). The estimated absolute difference for the 5- fraction versus 15-fraction schedule was 2.9% (90% CI, – 5.4% to 11.2%). The RRSE did not differ significantly between groups (Figure 2). Grade 1 fibrosis appeared more frequent in the 5-fraction arm. However, an imbalance was already present at baseline prior to WBI due to surgery (5-fr, 45%; 15-fr, 31%). Grade 3 fibrosis was rare, occurring in only 2 patients (1%) in each group. With median follow-up of 35.5 months [IQR, 25.7 – 59.8 months], 22 breast cancer events (15- fractions, 6; 5-fractions, 16) occurred. Disease-free survival (DFS) was not statistically different between
groups (p = 0.055). Conclusion:
The upper bound of the confidence interval (11.2%) exceeded the predefined non-inferiority margin (10%).Therefore, non-inferiority of 28.5 Gy in five fractions over 12 days compared with 40.05 Gy in 15 fractions over 3 weeks could not be demonstrated. Nevertheless, rates of grade 2/3 fibrosis were not increased in the 5-fraction arm, and the observed excess of grade 1 fibrosis in the 5-fraction arm was already present at baseline. Other RRSE outcomes were comparable and no differences in DFS were observed. This suggests that overall, the 5-fraction regimen with SIB appears safe and well-tolerated. References: Monten C. et al. Highly Accelerated Irradiation in 5 Fractions (HAI-5): Feasibility in Elderly Women With Early or Locally Advanced Breast Cancer. Int. J. Radiat. 2017; 98(4): 922– 930. https://doi.org/10.1016/j.ijrobp.2017.01.229Van Hulle H. et al. Acute toxicity and health-related quality of life after accelerated whole breast irradiation in 5 fractions with simultaneous integrated boost. Breast 2021; 55: 105–111. https://doi.org/10.1016/j.breast.2020.12.009 Keywords: Hypofractionation, boost, breast retraction Toxicity and Cosmetic Outcomes of 28 Gy in 5 Fractions Ultrahypofractionated Whole-Breast Irradiation in Early-Stage Breast Cancer Tanun Jitwatcharakomol 1,2 , Yevgeniya Gokun 3 , Rebekah L. Young 2 , Jacob M. Eckstein 2 , Therese Y. Andraos 2 , Steve A. Walston 2 , Kaidi Wang 2 , Pavnesh Kumar 2 , Eric R. Cochran 2 , Sasha J. Beyer 2 , Sachin R. Jhawar 2 1 Division of Radiation Oncology, Department of Radiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand. 2 Department of Radiation Oncology, The Ohio State University Wexner Medical Center, Columbus, USA. 3 Center for Biostatistics, , The Ohio State University Wexner Medical Center, Columbus, USA Purpose/Objective: The UK FAST and FAST-Forward trials established the non-inferiority of ultrahypofractionated whole-breast irradiation delivered in five fractions with respect to local control, toxicity, and cosmetic outcomes. However, the optimal regimen and technical approach for ultrahypofractionated adjuvant radiotherapy remain uncertain. Material/Methods: This retrospective, single-institution study included women with ductal carcinoma in situ (DCIS) or early- Digital Poster 1651
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