ESTRO 2025 - Abstract Book

S438

Clinical - Breast

ESTRO 2025

References: Risk of coronary artery disease after adjuvant radiotherapy in 29,662 early breast cancer patients: A population based Danish Breast Cancer Group study.” Milo, Marie Louise Holm et al. Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology vol. 157 (2021): 106-113. doi:10.1016/j.radonc.2021.01.010 Laterality of Radiation Therapy in Breast Cancer is Not Associated With Increased Risk of Coronary Artery Disease in the Contemporary Era. Seth, Lakshya et al. Advances in Radiation Oncology, Volume 9, Issue 10, 101583

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Proffered Paper DBCG Recommendations for Organs at Risk Dose Limits in Breast Cancer Radiotherapy: Analysis of Danish National Trial Data Ebbe L Lorenzen 1,2 , Henrik D Nissen 3 , Sami AlRawi 4 , Karen Andersen 5 , Kristian Boye 6 , Kirsten L Jakobsen 7 , Ingelise Jensen 8 , Else Maae 3 , Maja V Maraldo 9,10 , Louise W Matthiessen 11 , Mette Møller 8 , Esben S Yates 12 , Birgitte V Offersen 13,14 1 Laboratory of Radiation Physics, Odense University Hospital, Odense, Denmark. 2 Department of Clinical Research, University of Southern Denmark, Odense, Denmark. 3 Department of Oncology, Vejle Hospital, Vejle, Denmark. 4 Department of Oncology, Næstved Hospital, Næstved, Denmark. 5 Department of Radiation Physics, Copenhagen University Hospital Herlev and Gentofte, Herlev, Denmark. 6 Department of Oncology, Rigshospitalet, Copenhagen, Denmark. 7 Radiotherapy Department, Næstved Hospital, Næstved, Denmark. 8 Department of Oncology, Aalborg University Hospital, Aalborg, Denmark. 9 Dept of Oncology, Copenhagen University Hospital – Rigshospitalet, Copenhagen, Denmark. 10 Dept of Clinical Medicine, University of Copenhagen, Copenhagen, Denmark. 11 Department of Oncology, Copenhagen University Hospital Herlev and Gentofte, Herlev, Denmark. 12 Department of Medical Physics, Aarhus University Hospital, Aarhus, Denmark. 13 Department of Experimental Clinical Oncology, Aarhus University Hospital, Aarhus, Denmark. 14 Clinical Institute, Aarhus University, Aarhus, Denmark Purpose/Objective: Postoperative radiotherapy (RT) for breast cancer significantly improves survival, and severe late radiation-induced side effects are generally rare. However, minimizing radiation exposure to organs at risk (OARs) remains crucial to reduce long-term complications. Many late effects follow a linear dose-response relationship, making firm dose thresholds difficult to establish. This study aimed to define "typical maximum limits" for OAR doses based on dosimetric data from two large Danish Breast Cancer Group (DBCG) trials, with the additional goal of preparing the guidelines for new treatment techniques, such as Volumetric Modulated Arc Therapy (VMAT). Material/Methods: Key dose metrics for OARs — heart, both lungs, and contralateral breast — were selected based on a literature review. DICOM data from two large clinical trials, DBCG SKAGEN 1 and DBCG HYPO 1, were analyzed. 320 patients from the HYPO trial (breast only RT) and 300 patients from the SKAGEN trial (breast/chest wall and lymph nodes including the internal mammary nodes) was selected respectively as the 80 or 50 most recently treated patients from the respective four or six Danish centers in each trial. Only patients treated in the hypo-fractionated arms of the two studies (40 Gy in 15 fractions or similar integrated boost fractionations) were included. OARs and target regions were delineated according to ESTRO guidelines. The 80th and 95th percentiles of dose data were used to set two thresholds, reflecting moderate and rare deviations from typical doses. The mean dose was selected as the primary metric for all organs in this study. Results: Figure 1 shows center-specific OAR doses, revealing inter-center variability in OAR exposure. This variation highlights the importance of evenly distributing data from each center in establishing national dose thresholds. The recommended dose thresholds, summarized in Table 1, were rounded to the nearest 0.5 Gy to simplify clinical implementation.