Multi-phases Dose Analysis of Cardiac Substructures using Coronary CT Angiography in Postmastectomy Radiotherapy

This study used coronary computed tomography angiography (CCTA) in left breast cancer patients. It assessed real-time dose delivery of postmastectomy radiotherapy (PMRT) with internal lymph node irradiation (IMNIs) and normal tissue complications probability (NTCP) to the heart and subcardiac structures using tangential volumetric modulated arc therapy (T-VMAT). This research and its findings are critical in refining PMRT strategies to safeguard patient health and promote the overall efficacy of cancer management protocols. In this study, CCTA images from 16 patients were analyzed. These images were reconstructed at multiple phases (0%-90%) of the cardiac cycle for each patient. Substructures including the left ventricle (LV), right ventricle (RV), right atrium (RA), left atrium (LA), right coronary artery (RCA), and left anterior descending artery (LAD) were delineated using the RTOG 1106 OAR atlas guidelines. A rigid registration process aligned the CCTA images with planning chest CT scans. The heart's CT values were adjusted to ensure accuracy in electron density representation. The PTV was simulated, and a T-VMAT plan was created. The radiation fields were then applied to the 10 different cardiac phase images, and an accumulated plan was generated and compared with a conventional radiotherapy plan. Comparing the accumulated plan with the conventional plan, the absolute Dmean difference to the heart was 73.2 (cGy), and demonstrated a significant change of 14%. Among cardiac substructures, the largest differences in Dmean were observed in the LAD, RCA and LV-V25 with a variation of 387.5 cGy (22.5%), 195.8 cGy (34.7%) and 1.53% (52%), respectively. NTCP was slightly higher in the accumulated plan (0.44±1.57%) than in the conventional plan (0.17±0.47%). The results of this study underscore the critical role of real-time cardiac imaging in refining the delivery of PMRT with IMNIs. By leveraging CCTA and T-VMAT, we have achieved a more precise assessment of the cardiac dose, leading to a potential reduction in radiation-related cardiovascular risks without compromising cancer treatment efficacy. This research highlights the importance of integrating advanced imaging and radiation planning techniques to ensure the highest standards of patient care in the context of left breast cancer treatment.