Cardiac substructure dose and the risk of arrhythmia after curative radiotherapy for thymic tumors

Radiotherapy (RT) for thymic tumors often involves cardiac exposure. We evaluated the association between cardiac substructure dosimetry and post-RT arrhythmia.

This retrospective study included patients with thymic cancer or thymoma who underwent curative-intent radiotherapy between 2016 and 2024 and had available treatment plans. Cardiac substructures were auto-contoured, and mean doses, V5_Gy, and V30_Gy were calculated. Receiver operating characteristic curve analysis identified cutoff values for cardiac substructure dosimetric parameters. Univariate and multivariate analyses were performed using a competing risk model.

Among 100 patients (median follow-up, 47 months), 19 (19%) developed substantial arrhythmic events after thoracic radiotherapy. The 1-, 2-, and 5-year cumulative incidences of arrhythmia, adjusted for the competing risk of death, were 5.1%, 8.9%, and 24.4%, respectively. Patients with arrhythmic events had higher baseline World Health Organization (WHO) cardiovascular disease (CVD) risk scores and higher cardiac doses, including mean whole-heart, left atrium, left ventricle, and right ventricle doses. Receiver operating characteristic curve analysis identified predictors of arrhythmia: WHO CVD risk score > 6%, mean whole-heart dose > 2594 cGy, mean left atrium dose > 2388 cGy, mean left ventricle dose > 730 cGy, and mean right ventricle dose > 1236 cGy. In multivariate analysis, WHO CVD risk score and mean whole-heart dose remained independent predictors of arrhythmic events.

Substantial arrhythmic events after radiotherapy for thymic cancer or thymoma were associated with the baseline WHO CVD risk score and mean whole-heart dose. Implementing stricter cardiac dose constraints is essential to mitigate long-term toxicity in this potentially long-surviving cohort.