ESTRO 2025 - Abstract Book

S168

Brachytherapy -Breast

ESTRO 2025

Hannoun-Levi JM, et al. Second Conservative Treatment for Local Recurrence Breast Cancer: A GEC-ESTRO Oncological Outcome and Prognostic Factor Analysis. Int J Radiat Oncol Biol Phys. 2023 Dec 1;117(5):1200-1210. doi: 10.1016/j.ijrobp.2023.06.075.

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Digital Poster Kilovoltage Intraoperative Radiotherapy or EBRT Boost in early-stage high-risk breast cancer: a matched pair analysis Gustavo R. Sarria 1 , Adela Heredia 2 , Jorge Fernandez Quiroz 2 , Jose Burgos Mendez 2 , Eleni Gkika 1 , Gustavo J. Sarria 2 , Paola Fuentes-Rivera 2 1 Department of Radiation Oncology, University Hospital Bonn, Bonn, Germany. 2 Department of Radiotherapy, Instituto Nacional de Enfermedades Neoplasicas, Lima, Peru Purpose/Objective: To evaluate the clinical effectiveness of an upfront intraoperative radiotherapy (IORT) boost against sequential external-beam (EBRT) in a limited-resource setting, before the adoption of simultaneous integrated boost (SIB). Material/Methods: Patients from a large terciary refereral center, treated between 2014 and 2019 were retrospectively assessed and included. The IORT cohort encompassed patients prospectively recruited within an institutional registry, who were treated with a miniaturized linear accelerator with a low-energy x-ray output. A total 202 patients per arm where included in the analysis and matched per T and N stage, age at diagnosis, year of treatment, and systemic treatment features. The analysis was performed using the t-test or the non-parametric Mann-Whitney test. The association of qualitative variables with the treatment received, either IORT or EBRT, was analyzed using the Chi-square test through contingency tables. The condition of having no more than 20% of the cells with expected values less than 5 was verified. If this condition was not met, categories of the qualitative variable were grouped. For 2x2 contingency tables, the Yates correction was applied. Cummulative local control, cancer-specific survival and overall survival were evaluated and reported according to the Kaplan-Meier method. Results: Median follow-up was 57,5 and 58 months for IORT and EBRT, respectively. No significant imbalances were detected between both groups. The median age was 51 years old in both cohorts (p=0.987). Patients in both arms underwent similar systemic therapies (hormone therapy 77.1% vs. 76.6%, p=0.906; adjuvant chemotherapy 74.8% vs 75.2%, p=0.909). More patients in the IORT group showed G3 histologies (47.2% vs 30.2%, p=0.004) and in-situ component in the final pathology (41.6% vs 23.2%, p<0.001). Hypofraction was employed in 58.2% and 76.7% of patients (p<0.001). The 5-year cumulative local-recurrence rates were 3.4% and 2.4%, respectively (p=0.37). The cumulative 5 year nodal-recurrence rates were 1.6% and 0.6% (p=0.8), while the distant-metastases rates were 5.5% vs 5.1% (p=0.72). The 5-year estimated cancer-specific survival was 95.4% vs. 98.6% (p=0.72) and estimated overal survival 91.5% vs. 98% (p=0.11) with total 17 and 16 events along the follow-up period.