Dosimetric evaluation of cardiac substructures in DIBH-VMAT and FB- VMAT in hypofractionated radiotherapy for left-sided breast cancer: a comparative planning study

Background Left-sided breast cancer patients require particular attention due to cardiovascular structures adjacent to the treatment field that are likely to be affected by radiation.Radiation-induced cardiac toxicities are the most frequent treatment-related toxicities in left-sided breast cancer patients and have been widely investigated. To mitigate the risk of cardiac toxicities, cardiac-sparing techniques such as deep-inspiration breath-hold (DIBH) and intensity-modulated radiotherapy (IMRT) ,Volumetric modulated arc therapy ( VMAT)have been developed. Besides the heart, cardiac substructures are also being studied lately in the context of dose to OARs.Nevertheless, the reported data on the correlation between doses to cardiac substructures and cardiac changes during or post-radiotherapy are limited. Purpose To add new quantitative data to the existing literature,the aim of this study was to evaluate the OARs dosimetry of left-sided breast radiotherapy in terms of heart and heart substructures comparatively in free breathing and deep inspiration breath hold technique with volumetric-modulated arc radiotherapy. Materials and methods The study enrolled 30 female patients with confirmed left-sided breast cancer treated at our department during 2022–2024 with 3D-conformal radiotherapy (3DCRT) using 6MV Elekta Synergy Platform with Agility multileaf collimator. While patients were treated with 3D conformal plans, VMAT plans on free breathing and deep inspiration breath hold ( DIBH )were also made on the Monaco treatment. The OARs of interest for this study were the heart and the following substructures were contoured : pulmonary vein (PV), left atrium(LA), left ventricle (LV), right atrium (RA), right ventricle(RV), Sinoatrial Node ( SA node),Atrioventricular node ( AV Node). Dose and volume differences between treatment plans were evaluated by the Wilcoxon signed-rank test using SPSS software version 27. Result There is a statistically significant reduction in mean doses of heart, left anterior descending artery mean dose ,left ventricle ,left atrium ,right atrium, right ventricle with DIBH technique as shown in Table 1. Conclusion Cardiac substructures should be contoured additionally to the heart in view of a more complex dosimetric assessment and patient monitoring.Cardiac-sparing optimization technique like DIBH is most integral part while treating left sided breast cancer to reduce doses to cardiac substructure .