ESTRO 2025 - Abstract Book

S427

Clinical - Breast

ESTRO 2025

SEQB and SIB respectively. Compared to SEQB, the SIB significantly reduced the V 107% in both WB (5.9% versus 2.1% for SIB, p<0.0001) and TB (2.7% versus 0.03% for SIB, p<0.0001). The SIB technique improved the WB conformity index (0.2 [0.02-0.51] versus 0.31 [0.07-0.6] for SIB, p<0.0001) and decreased the WB heterogeneity index (1.41 [1.03-1.56] versus 1.2 [1.03-1.4] for SIB, p<0.0001). SIB significantly reduced V8 lung (9.8% [2.63-19.6] versus 10.6% [3.43-19.8] for SEQB, p < 0.001) and V1.5 Gy heart (8.9% [0-22.3] versus 10.53% [0.05-24.5] for SEQB, p = 0.0007). There was no significant difference between the 2 techniques for V 7 Gy heart (1.9% [0-5.3] versus 1.94% [0-5.44] for SEQB, p = 0.09). Conclusion: The SIB technique significantly improves the CI, reduces the risk of high doses in the target volume and OAR. In 3D UHF-RT, the SIB technique is both cost-effective and straightforward to implement, optimising the use of machines and reducing the treatment time for patients.

Keywords: Breast cancer, Ultrahypofractionated RT, SIB

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Digital Poster Minimizing Cardiac Risk: The Role of Coronary Artery and Heart Delineation in Breast Cancer Radiotherapy Virginia García Reglero 1 , Sara Vazquez Gonzalez 1 , Luis Ramos García 2 , Priscila Bernard Contreras 1 , Jose David Gonzalez Gomez 1 , Lucia Tueros Farfan 1 , Manuela Bermudez Zubiria 1 , Marta Bonet Beltran 1 , J Enrique Baquedano Baquedano 1 , Elena Garcia Alonso 1 , Moises Mira Flores 1 1 Radiation Oncology, Hospital Arnau de Vilanova, Lleida, Spain. 2 Medical Physics, Hospital Arnau de Vilanova, LLeida, Spain Purpose/Objective: Radiotherapy is a mainstay treatment for breast cancer. However, cardiac toxicity remains a significant concern. Precise delineation of cardiac structures, including coronary arteries, during radiotherapy planning is essential for minimizing radiation exposure to the heart and reducing the risk of adverse cardiac events. Material/Methods: This study aims to conduct a comparative dosimetry analysis between two cohorts of left-sided breast cancer patients undergoing radiotherapy. The historical cohort, where cardiac delineation was employed but coronary artery (CA) delineation was not, will be compared to a contemporary cohort where both cardiac and coronary artery structures are delineated. The primary objective is to assess the impact of delineating the coronary arteries on the radiation dose delivered to these critical structures. Secondary objectives may include evaluating potential differences in treatment planning parameters, dose-volume histogram metrics, and clinical outcomes between the two cohorts. Ultimately, this study seeks to quantify the potential benefits of incorporating coronary artery delineation into radiotherapy planning for left-sided breast cancer patients. Results: The results showed that the mean dose received by the CA was significantly higher in the group that did not delineate the CA. (p Mann-Whitney U = 0.012)