S234
Clinical - Breast
ESTRO 2026
adequate skin dose. Historically, bolus application was standard in all Danish Breast Cancer (DBCG) PMRT treatments but, from 2017 it was limited to T3–T4 disease and from 2022 to skin-invading disease (T4b- d). Using data from the randomised phase III DBCG Skagen Trial 1, this study evaluated the impact from bolus on late effects, particularly telangiectasia and local recurrence. Material/Methods: The Skagen Trial 1 randomised 2,963 high-risk breast cancer patients (2015–2021) to 50Gy in 25 fractions or 40Gy in 15 fractions. This analysis included 1,378 PMRT patients from centers enrolling minimum 50 patients. Annual specialist-reported assessments of loco-regional morbidity were conducted yearly from baseline to 5 and at 10 years. Cumulative incidence was used to estimate 3- and 5-year event rates for telangiectasia and local recurrence, accounting for competing risks. Results: Of the 1378 PMRT patients, 108 patients were excluded due to missing bolus or telangiectasia data, thus 1,273 patients were analysed, of whom 696 (55%) had bolus. 633 patients received 50Gy and 640 received 40Gy. Patient and tumor characteristics were well balanced between groups. Median follow up was 5.5 years. Telangiectasia occurred more frequently with bolus use, with a 5-year cumulative incidence of 67.0% (95% CI: 56.0–75.8) versus 18.6% (95% CI: 13.9– 23.9) without bolus, corresponding to an absolute difference of 48.4% (95% CI: 37.2–59.5). Bolus use was not associated with differences in other late morbidities, including induration, pain, and lymphedema (all p > 0.05). Twenty-one patients developed a local recurrence: 11 (1.6%) with bolus and 10 (1.7%) without (5-year cumulative incidence 1.6% [95% CI: 0.8–2.8] vs 1.8% [95% CI: 0.9–3.1]), no significant difference. Findings were consistent across both dose-fractionation regimens, with no significant interaction between dose and bolus use.
Proffered Paper 1219 Late effects and local recurrences after postmastectomy radiotherapy using bolus – results from the DBCG Skagen Trial 1 Bjarke Godske Baisner 1 , Jan Alsner 2 , Hanne Melgaard Nielsen 3 , Mette Holck Nielsen 4 , Maja Vestmø Maraldo 5 , Else Maae 6 , Ingvil Mjaaland 7 , Carine Kirkove 8 , Sami AlRawi 9 , Tamas Lörincz 10 , Egil Støre Blix 11 , Unn-Miriam Kasti 12 , Mechthild Krause 13 , Louise Wichmann Mathiessen 14 , Andreas Schreiber 15 , Maj-Britt Raaby Jensen 16 , Jens Overgaard 17 , Birgitte Vrou Offersen 18 1 Dep. of experimental clinical oncology, Aarhus University Hospital, Aarhus University, Aarhus, Denmark. 2 Dep. of experimental clinical oncology, Aarhus University Hospital, Aarhus, Denmark. 3 Department of oncology, Aarhus University Hospital, Aarhus, Denmark. 4 Department of oncology, Odense University Hospital, Odense, Denmark. 5 Department of oncology, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark. 6 Department of oncology, Vejle Hospital, Vejle, Denmark. 7 Department of oncology, Stavanger University Hospital, Stavanger, Norway. 8 Cliniques Universitaires St-Luc, Radiotherapy Department, Université Catholique de Louvain, Brussels, Belgium. 9 Department of Oncology, Zeeland University Hospital, Næstved, Denmark. 10 9Department of Oncology, Aalborg University Hospital, Aalborg, Denmark. 11 Department of Clinical Medicine, UiT The Arctic University of Norway, and Department of Oncologyof Clinical Medicine, Department of oncology, University Hospital of North Norway, Tromsø, Norway. 12 Department of Oncology, Hospital of Sørlandet, Kristiansand, Norway. 13 Department of Radiation Oncology and OncoRay, University Hospital and Faculty of Medicine Carl Gustav Carus, Technische Universität Dresden, German Cancer Consortium (DKTK) Dresden, Helmholtz-Zentrum Dresden- Rossendorf, National Center for Tumor Diseases (NCT) Dresden, and German Cancer Research Center (DKFZ), Heidelberg, Germany. 14 Department of oncology, Copenhagen University Hospital Herlev and Gentofte, Herlev, Denmark. 15 Department of Oncology and Praxis for Radiotherapy, Academic Teaching Hospital Dresden-Friedrichstadt, Dresden, Germany. 16 Danish Breast Cancer Group, Department of Oncology, Copenhagen University Hosptial, Rigshospitalet, Copenhagen, Denmark. 17 Department of Experimental Clinical Oncology, Aarhus University Hospital, and Aarhus University, Aarhus, Denmark. 18 Dep. of experimental clinical oncology, Aarhus University Hospital, and Aarhus University, Aarhus, Denmark Purpose/Objective: A tissue-equivalent bolus is often applied during postmastectomy radiotherapy (PMRT) to ensure
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