Dosimetric relevance of mean heart dose in predicting exposure to cardiac substructures in radiotherapy for breast cancer: A prospective observational study

Background: Radiotherapy offers significant clinical benefits in breast cancer management; however, its long-term survival benefits are limited by cardiac-related late effects and mortality. Objectives: The primary objective was to evaluate the relevance of mean heart dose (MHD) as a predictor of exposure to cardiac substructures. Secondary objectives included estimation of radiation exposure to specific cardiac chambers and the coronary vessels. Materials and Methods: This prospective observational study was conducted in the Department of Radiation Oncology, Acharya Harihar Postgraduate Institute of Cancer, from July 2021 to July 2023. Fifty individuals with carcinoma breast post-modified radical mastectomy received adjuvant radiotherapy using 3D conformal radiotherapy. For each patient, target volume, heart, cardiac chambers, and cardiac-vessels were contoured, and mean heart dose, D mean , D2, and V5 of each cardiac substructure were calculated from dose-volume histogram and analyzed using linear regression. Results: We included 50 patients in the study. The linear regression coefficient (R 2 ) values for D mean of the left ventricle (LV) with MHD and left anterior descending artery (LAD) with MHD in left-sided breast cancer were 0.061 and 0.196, respectively. For patients with right-sided breast cancer, these values were 0.102 (LV) and 0.099 (MHD). In patients with left-sided carcinoma, MHD correlated most strongly with the LAD (r = 0.606, P = 0.001), while in patients with right-sided carcinoma, the most notable correlation was found for the left atrium (r = 0.686, P , 0.001). Other structures had weak correlations. Conclusion: To effectively study radiation induced cardiotoxicity, MHD alone would not suffice, and dose to each cardiac substructure may be necessary.