Cardiac Conduction System as an OAR in Radiation Therapy: Doses to SA/AV Nodes and Their Reduction

Despite advancements in radiation techniques, concerns persist regarding the adverse effects of radiation therapy, particularly cardiotoxicity or radiation-induced heart disease. Recently, arrhythmogenic toxicity has come to the forefront-the impact of radiation therapy on the cardiac conduction system. Our objective was to conduct a dosimetric study and subsequently investigate the feasibility of optimizing the sinoatrial (SA) and atrioventricular (AV) nodes as organs at risk (OARs) in proton radiation therapy for non-small cell lung cancer with N3 disease. Thirty-two non-small cell lung cancer patients with N3 disease undergoing proton radiation therapy were included. Sinoatrial and AV nodes, along with standard OARs, were delineated. Dosimetric analysis and optimization were performed using intensity-modulated proton therapy. Patients surpassing a predefined SA node dose threshold underwent dose optimization. Proton radiation therapy with pencil beam scanning demonstrated a significant reduction in SA and AV node doses without compromising target volume coverage or significant shift in the dose to other monitored OARs. Dose reduction to the SA and AV nodes for pencil beam scanning is a relatively simple task, and the reduction can be very substantial. Larger cohort studies and diverse radiotherapeutic modalities are needed for further validation and refinement of dose constraints.