S327
Clinical - Breast
ESTRO 2026
of radiation-induced toxicities. Therefore, understanding the radiation dose distribution to specific cardiac regions across various radiotherapy techniques is crucial(2). Traditionally, the mean heart dose (MHD) has been the principal cardiac constraint; however, recent evidence underscores the need to evaluate substructure-specific doses. This study assesses radiation exposure to individual cardiac chambers and the left anterior descending artery (LADA), comparing dose distributions between three- dimensional conformal radiotherapy (3DCRT) and volumetric modulated arc therapy (VMAT) in post- mastectomy breast cancer patients. Material/Methods: This prospective, randomized study included 104 patients with histologically confirmed breast carcinoma who underwent modified radical mastectomy between 2023 and 2025. All patients received adjuvant radiotherapy to the chest wall and regional lymphatics with curative intent and were randomized to either 3DCRT (30 left-sided, 23 right- sided) or VMAT (30 left-sided, 21 right-sided). Immobilization, CT simulation, and treatment planning were performed for all participants. Radiotherapy was delivered as 40 Gy in 15 daily fractions over three weeks. Cardiac substructures—including the right atrium (RA), left atrium (LA), right ventricle (RV), left ventricle (LV), and LADA—were delineated on CT images. Plans were optimized for target coverage while minimizing dose to OARs, with predefined hard and soft whole heart constraints. Statistical analysis was performed using Microsoft Excel, with p ≤ 0.05 considered significant. Results: Table 1:Radiation dose to cardiac substructures
For left-sided cases, VMAT demonstrated significantly lower MHD (603.06 ± 185.5cGy) compared to 3DCRT (812.36 ± 295.01cGy), and a reduced mean dose to LV (789.94 ± 319.77cGy vs. 1377.25 ± 994.45cGy). In contrast, 3DCRT provided superior cardiac sparing in right-sided breast cancers(Table1). Conclusion: In our study, for left-sided breast cancer, VMAT effectively minimized exposure to critical cardiac substructures namely LV and LADA, whereas 3DCRT resulted in lower cardiac doses for right-sided cases. Applying radiotherapy dose constraints to the whole heart alone was insufficient to protect key cardiac substructures. These findings emphasize the importance of individualizing radiotherapy technique selection according to tumor laterality and highlight the need to incorporate targeted substructure constraints to mitigate the risk of cardiotoxicity. References: (1)Kang Z, Chen S, Shi L, He Y, Gao X (2021) Predictors of heart and lung dose in left-sided breast cancer treated with VMAT relative to 3D-CRT: A retrospective study. PLoS ONE. 2021;16(6): e0252552. doi:10.1371/journal.pone.0252552.(2) Li X, Wu Y, Wang Q, Li B, Wang J. Radiation-induced cardiac substructure damage and dose constraints: a review. Radiat Oncol. 2025 Jun 5;20(1):94. doi: 10.1186/s13014-025-02668-x.
PMID: 40474260; PMCID: PMC12139131. Keywords: Cardiac dosimetry, Left ventricle
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