Mediastinal critical structures such as trachea, bronchus, esophagus, and heart are among the dose-limiting factors for stereotactic body radiation therapy (SBRT) to central lung lesions. The purpose of this study was to characterize the risk of esophagitis for patients treated with SBRT and to develop a statistical dose-response model to assess the equivalent uniform dose, D-10%, D-5 (cc), D-1 (cc), and D-max, to the esophagus and the risk of toxicity. Toxicity outcomes of a dose escalation study of 56 patients who had taken CyberKnife treatment from 45-60 Gy in 3-7 fractions at the Erasmus MC-Daniel den Hoed Cancer Center were utilized to create the dose response model for esophagus. A total of 5 grade 2 esophageal complications were reported (Common Terminology Criteria for Adverse Events version 3.0); 4 complications were early effects and 1 complication was a late effect. All analyses were performed in terms of 5-fraction equivalent dosing. According to our study, D-1 (cc) at a dose of 32.9 Gy and D-max dose of 43.4 Gy corresponded to a complication probability of 50% for grade 2 toxicity. In this series of 58 CyberKnife mediastinal lung cases, no grade 3 or higher esophageal toxicity occurred. Our estimates of esophageal toxicity are compared with the data in the literature. Further research needs to be performed to establish more reliable dose limits as longer follow-up and toxicity outcomes are reported in patients treated with SBRT for central lung lesions. (C) 2016 Elsevier Inc. All rights reserved.