Backgound: We retrospectively investigated the clinical characteristics and outcome of pneumothorax after stereotactic body radiotherapy (SBRT) for lung tumors. Methods: Between April 2003 and July 2012, 473 patients with lung tumors were treated with SBRT. We identified 12 patients (2.5 %) with pneumothorax caused by SBRT, and evaluated the clinical features of pneumothorax. Results: All of the tumors were primary lung cancers. The severity of radiation pneumonitis was grade 1 in 10 patients and grade 2 in two patients. Nine patients had emphysema. The planning target volume and pleura overlapped in 11 patients, and the tumors were attached to the pleura in 7 patients. Rib fractures were observed in three patients before or at the same time as the diagnosis of pneumothorax. The median time to onset of pneumothorax after SBRT was 18.5 months (4–84 months). The severity of pneumothorax was grade 1 in 11 patients and grade 3 in one patient. Conclusion: Although pneumothorax was a relatively rare late adverse effect after SBRT, some patients demonstrated pneumothorax after SBRT for peripheral lung tumors. Although most pneumothorax was generally tolerable and self-limiting, careful follow-up is needed.
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