ESTRO 2025 - Abstract Book

S494

Clinical - Breast

ESTRO 2025

by factors, including age, prior ipsilateral breast cancer, screening detection, morphology, molecular subtype, multifocality, intra-/extra-tumoral DCIS besides IBC, differentiation grade and hospital type. Higher cT stage increased the likelihood of MRI use, while higher pN stage and involved tumor margins lowered the likelihood of PBI. For patients meeting ASTRO PBI criteria (unifocal cT1, grade 1/2, ER-positive, pure DCIS ≤2,5 cm), MRI use was associated with a decreased likelihood of PBI in IBC (adjusted odds ratio (OR):0.66, 95% confidence interval (CI):0.60 0.72 and DCIS (OR:0.80, 95% CI:0.75-0.85). Consequently, the probability of receiving whole breast irradiation increased with MRI in IBC (OR 1.29, 95% CI:1.24-1.34) and DCIS (OR 1.85, 95% CI:1.72-1.98). Additionally, MRI was associated with fewer DCIS-involved margins in IBC (OR 0.81, 95% CI:0.74-0.89), and a higher probability of mastectomy (OR 1.29, 95% CI:1.24-1.34), but did not affect the probability of a re-excision (OR 0.93, 95%CI: 0.87 1.00).

Conclusion: This study shows rising trends in MRI and PBI use, along with a steady combination of MRI and PBI in the Netherlands from 2011 to 2022. MRI facilitates detailed tumor assessment by identifying factors that reduce PBI suitability while enhancing surgical precision by lowering the rate of positive DCIS margins . Consequently, MRI plays a crucial role in guiding treatment decisions for patients eligible for PBI.

Keywords: MRI, partial breast irradiation, early-stage

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Digital Poster Does age matter? Assessing the impact of age on DIBH in radiotherapy Rebecca Moser 1 , Lena Marie Buchecker 1 , Mathias Düsberg 1 , Sophie Therese Behzadi 1 , Nina Mayr 2 , Sophia Kiesl 1 , Jana Nano 1 , Stephanie Elisabeth Combs 1,3,4 , Kai Joachim Borm 1 1 Department of Radiation Oncology, TUM School of Medicine and Health, Klinikum rechts der Isar, Technical University of Munich, Munich, Germany. 2 School of Human Medicine, Michigan State University, East Lansing, MI, USA. 3 Department of Radiation Medicine (IRM), Helmholtz Zentrum München (HMGU), Munich, Germany. 4 German Consortium for Translational Cancer Research (dktk), Partner Site Munich, Munich, Germany Purpose/Objective: Deep inspiration breath hold (DIBH) is regarded as the standard of care in adjuvant radiotherapy (RT) for patients with left-sided breast cancer (1). While previous studies have primarily focused on patients with a mean age under