ESTRO 2025 - Abstract Book

S463

Clinical - Breast

ESTRO 2025

Conclusion: In this cohort of breast cancer patients treated with helical tomotherapy, major coronary events were extremely rare and likely influenced by pre-existing risk factors. This supports the hypothesis that the linear relationship between MHD and cardiac events observed in 3D radiotherapy may not apply to IMRT, potentially leading to an overestimation of risk. Further studies with long-term follow-up are needed to refine dose constraints for IMRT.

Keywords: Tomotherapy ; Breast Cancer; Cardiac Toxicity

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Digital Poster Heart and lung sparing with isocentric lateral decubitus positioning compared with dorsal decubitus positioning for breast cancer radiotherapy

Pierre Loap, Jeremi Vu Bezin, Alain Fourquet, Youlia Kirova Department of Radiation Oncology, Institut Curie, Paris, France

Purpose/Objective: The cardiac and pulmonary dosimetric benefit of alternative positioning in isocentric lateral decubitus compared with dorsal decubitus during adjuvant breast irradiation has yet to be proven, in spite of the relative long-standing use of isocentric lateral decubitus. Material/Methods: Eight consecutive patients with an indication for adjuvant breast irradiation without boost or lymph node irradiation were scanned in both isocentric lateral and dorsal decubitus positions. For each patient, a plan delivering 40.05Gy in 15 fractions in isocentric lateral decubitus and in dorsal decubitus using a field-in-field technique were calculated. Doses to the heart, to various cardiac substructures and to the lungs were compared. Results: Mean dose to the heart, to various cardiac structures (left ventricle, left coronary, right coronary), to the homolateral lung and to the contralateral lung were significantly lower in isocentric lateral decubitus than in dorsal decubitus.From the dorsal decubitus to the isocentric lateral decubitus position, the median mean dose decreased respectively from 82.0 cGy to 74.0 cGy for the heart (p = 0.039), from 62.5 cGy to 58.0 cGy for the left ventricle (p = 0.022), from 142.5 cGy to 89.0 cGy for the right coronary artery (p = 0. 016), from 103.5 cGy to 82.0 cGy for the left coronary artery (p = 0.039), from 151.0 cGy to 91.0 cGy for the sino-atrial node (p = 0.058), from 107.5 cGy to 43.0 cGy for the homolateral lung (p = 0.008), and from 26.5 cGy to 19. cGy for the contralateral lung (p = 0.021). Average absolute mean dose reductions were -40 cGy for the heart, -27.5 cGy for the left ventricle, -56.5 cGy for the right coronary artery, -64.5 cGy for the left coronary artery, -45.5 cGy for the sino-atrial node, -74 cGy for the homolateral lung and -4.5 cGy for the contralateral lung. For all organs-at-risk, median dose-volume histograms in isocentric lateral decubitus showed lower relative volumes than in dorsal decubitus.