ESTRO 2025 - Abstract Book

S493

Clinical - Breast

ESTRO 2025

Conclusion: Distance to the proton treatment facility appeared as the most important barrier to participation in the DBCG Proton Trial, reflecting a common challenge in clinical trial enrolment [5]. Conversely, the prospect of reduced late effects was the primary motivator for those considering participation. The decision was challenging for most patients, with often one individual, dominant factor ultimately guiding their final choice.

Keywords: Trial participation, breast cancer, interviews

References: 1. Unger, J.M. et al. (2019). Barriers to cancer trial participation: A systematic review. *J Natl Cancer Inst*, 111(3), 245-255. DOI: 10.1093/jnci/djy221. 2. Manne, S. et al. (2015). Attitudinal barriers in oncology trials. *Eur J Cancer Care*, 24(1), 28-38. DOI: 10.1111/ecc.12180. 3. Stick, L.B. et al. (2021). DBCG proton trial selection criteria. *Clin Transl Radiat Oncol*, 27, 126-131. DOI: 10.1016/j.ctro.2021.01.012. 4. Kvale, S. & Brinkmann, S. (2015). *Interviews: A qualitative research guide* (3rd ed.). Gyldendal. 5. Gad, K.T. et al. (2019). Socioeconomic disparities in Phase I trial referrals. *J Clin Oncol*, 37(13), 1111-1119. DOI: 10.1200/jco.18.01983.

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Poster Discussion Trends in use of Magnetic Resonance Imaging and Partial Breast Irradiation between 2011-2022 in the Netherlands: a population-based study Yasmin A Civil 1,2 , Anouk H Eijkelboom 3 , Anne Veldink 3 , Marissa C van Maaren 3,4 , John H Maduro 5 , Katya M Duvivier 6 , Sabine Siesling 3,4 , Desirée van den Bongard 1 1 Radiation Oncology, Amsterdam UMC, Amsterdam, Netherlands. 2 Cancer Treatment and Quality of Life, Cancer Center Amsterdam, Amsterdam, Netherlands. 3 Research and Development, Netherlands Comprehensive Cancer Organisation (IKNL), Utrecht, Netherlands. 4 Health Technology and Services Research, Techinal Medical Center, Enschede, Netherlands. 5 Radiation Oncology, University Medical Center Groningen, Groningen, Netherlands. 6 Radiology, Amsterdam UMC, Amsterdam, Netherlands Purpose/Objective: Introduction: Trends in MRI and partial breast irradiation (PBI) were evaluated in the Netherlands from 2011 to 2022, including MRI´s impact on treatment strategies. Material/Methods: Methods: Women aged ≥50 years who underwent primary surgery for cT1-2N0M0 breast cancer or DCIS between 2011-2022 were selected from the Netherlands Cancer Registry. Trends in PBI use were analyzed on data from 2017-2022 reflecting the implementation of PBI for low-risk breast cancer in the Dutch guidelines since 2017. Multivariable logistic regression was used to analyze associations between patient-, tumor- and treatment-related characteristics and the use of MRI and PBI stratified by tumor type (invasive breast cancer (IBC) or DCIS). Sensitivity analyses were performed to assess the association between MRI and PBI in patients meeting ASTRO PBI criteria for both IBC and DCIS. Results: Results: In total, 119,768 women were included, with 35,863 (30%) receiving an MRI. MRI utilization increased from 2011 (24%) to 2022 (37%) (Figure 1). Among patients receiving radiotherapy, the proportion receiving PBI increased from 3% in 2017 to 21% in 2022. In the multivariable analysis of patients with IBC, MRI and PBI use were influenced