Abstract P1-10-16: Cardiac conduction system exposure with modern radiotherapy techniques for breast cancer irradiation

Introduction: Exposition of cardiac conduction system during breast radiotherapy has never been studied, despite increasing use of intensity modulated radiotherapy which expose larger volume to low dose bath. We evaluated conduction node exposure during breast irradiation with volumetric modulated arctherapy (VMAT) and estimated the potential dosimetric benefit with intensity modulated protontherapy (IMPT). Materials and methods: Atrioventricular (AVN) and sinoatrial (SAN) nodes were retrospectively delineated according to published guidelines on the simulation CT scans of twelve breast cancer patients having undergone conserving surgery and adjuvant locoregional VMAT. IMPT treatment was re-planned on the simulation CT scans for all breast cancer patients. Mean and maximum doses to the SAN and the AVN were retrieved and compared. Correlation coefficients were calculated between doses to the SAN or the AVN and to the whole heart. Results: Average mean doses to the SAN and to the AVN were 2.8 Gy and 2.3 Gy respectively for left-sided irradiation and 9.6 Gy and 3.6 Gy respectively for right-sided irradiation. Average maximum doses to the SAN and to the AVN were 3.5 Gy and 2.8 Gy respectively for left-sided irradiation and 13.1 Gy and 4.6 Gy respectively for right-sided irradiation. IMPT significantly reduces doses to conduction nodes. Correlations between doses to the SAN or the AVN and the whole heart were usually significant. Conclusion: SAN and AVN can be substantially exposed during breast VMAT, especially for right-sided irradiation. Cardiotoxicity studies evaluating conduction node exposure might define dose constraints and criteria for additional cardiac sparing techniques, such as respiratory techniques or proton therapy, which could be beneficial to patients with underlying rhythmic or conduction disorders. Citation Format: Pierre Loap, Farid Goudjil, Ludovic De Marzi, Vincent Servois, Krassen Kirov, Alain Fourquet, Youlia M. Kirova. Cardiac conduction system exposure with modern radiotherapy techniques for breast cancer irradiation [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-10-16.