Association of Cardiac Conduction System Radiation Doses with Incident Atrial Fibrillation in Lung Cancer.

Thoracic radiotherapy (RT) is linked to cardiovascular toxicity, but its impact on the cardiac conduction system, particularly the sinoatrial (SA) node, is poorly defined. We examined whether SA node radiation dose is associated with new-onset atrial fibrillation (AF), accounting for the competing risk of death. We retrospectively studied 84 lung cancer patients undergoing thoracic RT, stratified by maximum SA node dose (Dmax) using an exploratory, data-derived threshold of 17.23 Gy. Cumulative incidence functions and Fine-Gray regression, treating death as a competing event, assessed AF risk. Median age was 68.5 years; median follow-up was 12.0 months. AF occurred in 9 patients (10.7%). The high-dose SA node group (>17.23 Gy) was significantly younger (65.5 vs. 70.0 years; P=0.010) with similar Mayo AF Risk Scores (P=0.821), yet had a higher 24-month cumulative incidence of AF (18.8% vs. 4.1%; Gray's test P=0.038). AV node Dmax was not associated with AF but correlated with post-radiotherapy PR-interval prolongation (+14.1 ms; Spearman ρ=0.47, P=0.006). In an exploratory multivariable model adjusting for age, SA node Dmax remained associated with AF (adjusted sHR 1.04 per 1-Gy; 95% CI 1.01-1.06; P=0.008), warranting cautious interpretation given the limited event number. In this hypothesis-generating, single-center cohort, higher SA node dose was associated with increased AF incidence independent of age, while AV node dose was linked to PR prolongation rather than AF. These preliminary findings require validation in larger, prospective, multicenter cohorts before the SA node can be considered a formal organ at risk in RT planning.