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

PURPOSE: Radiotherapy (RT) for thymic tumors often involves cardiac exposure. We evaluated the association between cardiac substructure dosimetry and post-RT arrhythmia. MATERIALS AND METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.