High radiation dose to the main bronchi can result in stenosis, occlusion or fistula formation, and death. Only 8 articles have reported side effects to the main bronchi from stereotactic body radiation therapy (SBRD, mostly with only one symptomatic complication per article. Therefore, we calculated the dose to the bronchial structures, such as trachea; mainstem bronchi; intermediate bronchus; upper-, middle-, and lower-lobe bronchus; and the segmental bronchi in 134 patients with central tumors and calculated the normal tissue complication probability (NTCP) for each of these structures, with toxicity determination based upon computed tomography imaging. No side effects were found in the trachea, and only stenosis occurred in the main bronchus and bronchus intermedius. Higher grades of side effects, such as occlusion and atelectasis, were only seen in the upper-, middle-, and lower bronchi and the segmental bronchi. When 0.5 cc of a segmental bronchi was irradiated to 50 Gy in 5 fractions, it was about 50% likely to be occluded radiographically. For grade 1 radiographically evident side effects, the 50% risk level for a 5-fraction D-max was 55 Gy for mid-bronchi and 65 Gy for mainstem bronchi. To assure the relationship between clinical toxicity and side effects to the bronchi, further investigation is needed. (C) 2016 Elsevier Inc. All rights reserved.