2664 - Cardiopulmonary Substructure Doses are Not Correlated with Cardiorespiratory Fitness among Breast Cancer Survivors Treated with Contemporary Radiotherapy

M. Thor¹, J. Scott², A. Reiner², L. Hong¹, A. Yu², A. Apte¹, B. McCormick³, A. Perez-Andujar², C. Lee², L. I. Cervino¹, J. Harrison², X. Liang², P. Patel², L. T. Dauer², C. Moskowitz², and J. Bernstein²; ¹Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY, ²Memorial Sloan Kettering Cancer Center, New York, NY, ³Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY

Purpose/Objective(s): Breast cancer radiotherapy (RT) techniques have historically delivered mean heart doses (MHDs) in the range of 5 Gy, which have been found to predispose patients to cardiopulmonary toxicities. The purpose of this study was to evaluate whether cardiopulmonary substructure dose was associated with cardiorespiratory fitness in breast cancer survivors treated with state-of-the-art RT planning and delivery techniques. Materials/

Methods: Cardiopulmonary substructures were Artificial-Intelligence (AI) auto-segmented. Cardiorespiratory fitness was evaluated at a median of 2.3 (range: 1.1-9.8) years following RT in 2007-2021 among 65 breast cancer survivors. The associations between the mean dose to each of the nine AI auto-segmented cardiopulmonary substructures, the contralateral, and the ipsilateral lung with cardiorespiratory fitness were evaluated using linear regression.

Results: The median MHD was 0.64 Gy (range: 0.12-7.1). Among the auto-segmented substructures, the highest mean doses were observed for the left ventricle (median: 0.88 Gy). The mean dose to each of the eleven structures was significantly higher for women treated with volumetric-modulated arc therapy (VMAT; MHD median: 3.8 Gy vs. 0.57 Gy; p<0.0001). Women with left-sided breast cancer had significantly higher MHD (0.97 vs. 0.38 Gy; p<0.0001), due to higher doses in 3 of 4 cardiac chambers, and also significantly higher pulmonary artery dose (median: 0.93 vs. 0.32 Gy; p=0.0003); women with right-sided breast cancer had significantly higher vena cava and right atrium (RA) doses (e.g., RA; median: 0.74 vs. 0.29 Gy; p=0.0002). No cardiopulmonary structure dose was significantly associated with reduced cardiorespiratory fitness when adjusting for age, chemotherapy agent, and VMAT.

Conclusion: State-of-the-art breast cancer RT has reduced cardiopulmonary dose, and there is both a technique and cancer laterality RT dose dependence throughout the cardiopulmonary system.