ESTRO 2025 - Abstract Book

S616

Clinical - Breast

ESTRO 2025

Purpose/Objective: Cardiac toxicity resulting from irradiation of left-sided breast cancer(LBC) is widely recognized as dose-dependent. This single-institution prospective analysis aimed to evaluate whether radiation therapy(RT) delivered using the moderate deep inspiration breath hold(mDIBH) technique, assisted by the Active Breathing Coordinator(ABC), could effectively reduce the mean heart dose(MHD) and the maximum dose to the left anterior descending coronary artery(LAD). Previous findings from our institution demonstrated that this technique was well-tolerated across various treatment schedules and led to significant reductions in cardiac dose. In this study, we focus on the feasibility of this approach, specifically in elderly patients(pts), a population at heightened risk due to frailty and comorbidities. For these pts, ensuring safer and more convenient treatment options is of paramount importance. Material/Methods: We prospectively collected data from patients with LBC stages 0-III who underwent RT using the ABC/mDIBH technique to assess its efficacy and reproducibility. Eligible patients were those capable of tolerating mDIBH, willing to undergo device training, and able to perform a 20-second breath-hold. The primary endpoint was to compare ABC-assisted dosimetry with free-breathing(FB) plans, focusing on the reduction of MHD and maximum LAD dose. The secondary endpoint was the procedural success rate. Results: A total of 121elderly patients with stages 0-III LBC were enrolled from February 2021 to June 2024. The mean age was 75(70-89). 70 pts underwent left breast RT, using an ultrahypofractionated scheme of 26Gy in 5fractions over 1week and were able to use the mDIBH. 2 were bilateral, 8 received a simultaneous integrated boost(29Gy) according to tumor grading. Only 10 pts underwent FB RT due to: hypoacusia, and/or non-compliance in maintaining inspiratory apnea. The primary endpoint was achieved, showing a significant reduction in MHD with mDIBH (mean:0.7 Gy, range:0.2– 1.5Gy), compared to the FB technique (mean:1.394 Gy, range: 1.341–1.626Gy) (p < 0.001), as determined by Welch's t-test. Similarly, when considering the maximum LADdose, mDIBH (mean:4.78Gy, range:1.470–10.950 Gy) showed a significantly lower dose than FB (mean:6.05Gy, range:5.432–11.295 Gy), with a statistically significant difference (p=0.023). This technique was feasible in most of pts. The mean breath-hold volume was 1.1 L, and the mean breath hold duration was 25 s. No adverse events were reported. Conclusion: This study confirms previous findings that mDIBH-ABC technique significantly reduces cardiac dose. In our clinical practice, this is the preferred approach for cardiac sparing in LBC patients, demonstrating feasibility and safety also in elderly patients.

Keywords: elderly, ABC, mDIBH

4196

Digital Poster Impact of SBRT on systemic therapeutic line change in oligometastatic breast cancer Julie Leblanc 1 , Alexandre de Nonneville 2 , Camille Nicolas 1 , Anthony Goncalves 2 , Véronique Favrel 1 , Marguerite Tyran 1 , Morgan Guenolé 1 , Laurence Gonzague 1 , Leonel Varela 1 , Agnès Tallet 1 , Claire Petit 1 1 Radiotherapy, Institut Paoli-Calmettes, Marseille, France. 2 Medical Oncology, Institut Paoli-Calmettes, Marseille, France

Purpose/Objective: Breast cancer is the leading cancer among women in France; however, the management of oligometastatic disease