Cardiac Substructure Dose Response after Lung Cancer Radiotherapy

While curative radiation therapy provides excellent disease control for lung tumors, adverse cardiac events can occur from treatment. Due to the central proximity of the heart to the lungs, patients treated for lung cancer with radiation therapy are at heightened risk of increased cardiac radiation exposure. Conventionally, the whole heart is considered an organ-at-risk in which radiation dose should be minimized during treatment planning, employing strategic constraints such as maximum and mean dose. Emerging research highlights specific cardiac substructure doses, which are rarely utilized in clinical organ-at-risk planning, as more accurate predictors of postradiotherapy cardiac risk than whole heart dose alone. This review consolidates findings on substructure radiation doses associated with various cardiac outcomes to optimize lung treatment planning and guide development of thresholds, particularly for high-risk patients. Two PubMed searches identified 32 key studies published between 2017 and 2024. Radiation doses to heart chambers, conduction nodes, great vessels, coronary arteries, pericardium, and valves correlate with various adverse outcomes postradiotherapy. Minimizing radiation exposure to the left ventricle, left atrium, heart base, and left coronary arteries, including the left anterior descending and left circumflex arteries, is recommended. This systematic review supports the utilization of individual substructure doses rather than solely whole heart dose during lung radiotherapy planning to improve long term patient outcomes and wellbeing.