ESTRO 2025 - Abstract Book

S445

Clinical - Breast

ESTRO 2025

604

Digital Poster Comparative analysis of abdominal and thoracic deep inspiration breath holds on heart radiation dose in breast cancer radiotherapy Renée De Noyette 1 , Michael Stouthandel 1 , Vincent Vakaet 1,2 , Bruno Speleers 2 , Frederik Vanhoutte 2 , Pascal Pellegrin 3 , Vincent Remouchamps 3 , Françoise Kayser 3 , Tom Van Hoof 1 , Werner De Gersem 1,2 , Liv Veldeman 1,2 1 Department of Human Structure and Repair, Ghent University, Ghent, Belgium. 2 Department of Radiation Oncology, University Hospital Ghent, Ghent, Belgium. 3 Radiation Oncology, CHU UCL Namur, site Sainte Elisabeth, Namur, Belgium Purpose/Objective: Deep inspiration breath-hold (DIBH) significantly lowers radiation dose to the heart during left-sided whole-breast irradiation (1). The primary muscles involved in DIBHs are the diaphragm for abdominal (A-)DIBH and the intercostal muscles for thoracic (T-)DIBH. In abdominal breathing, the diaphragm and the connected heart move together to a more caudal position. This movement is expected to bring the heart more inferior to the irradiated breast and could therefore further reduce cardiac dose. This exploratory study analyzed anatomical differences between an A-DIBH and a T-DIBH in prone and supine positions to assess their impact on mean heart dose (MHD) reduction. Material/Methods: Ten healthy female adults received breath-hold training. Twelve magnetic resonance imaging (MRI) datasets were captured per participant during DIBHs in the prone and supine positions (2 T-DIBH + 2 A-DIBH + 2 free-breathing). For each MRI-dataset, left breast and heart were delineated and centroid displacements in x, y, and z-directions were analyzed. Distance volume histograms (DiVHs) were used to compare changes in position of the heart relative to the left breast. Di 50 values (50% of the heart’s volume lies closer to the left breast than the distance represented by the Di 50 value) were calculated and used to compare groups via two-tailed Wilcoxon matched-pairs signed-rank tests. Ethical approval was obtained. Participants gave prior informed consent and completed an MRI safety document. Results: Both DIBHs cause a medial, inferior and posterior movement of the heart in the prone position, while in supine position the heart moves anteriorly. Overall positional changes between an A-DIBH and T-DIBH were significantly different in prone position (p = 0.049). The heart-centroid shifts more between an A-DIBH and FB (18.12 mm) than between a T-DIBH and FB (15.82 mm). In supine position, no significant differences between A- and T-DIBH were found (p = 0.109). According to the DiVHs, there was a minor difference in heart - breast distance favoring T-DIBH over A-DIBH in both positions (Figure 1). Di 50 values significantly differed between A-DIBH and T-DIBH in prone (p value = 0.0098) and supine (p-value = 0.037) positions. The advantage of T-DIBH over A-DIBH was larger in prone position than supine position, as can be seen from the dDiVHs.