Spontaneous Pneumothorax During Stereotactic Body Radiotherapy for Pulmonary Metastasis From Osteosarcoma: A Case Report and Literature Review.

Pulmonary metastases represent the predominant pattern of distant disease in osteosarcoma and are associated with a spectrum of thoracic complications. Among these, spontaneous pneumothorax is an infrequent but clinically important event. Here, we present the case of a young man who developed spontaneous pneumothorax during the course of stereotactic body radiotherapy (SBRT) for a subpleural pulmonary metastasis delivered using the Deep Inspiratory Breath Hold (DIBH) technique. The pneumothorax was detected on routine image guidance after the fourth fraction of treatment. Despite this unexpected event, the patient remained clinically stable and was successfully managed conservatively with supplemental oxygen, allowing completion of SBRT following a brief treatment interruption. Interval imaging demonstrated rapid cavitary transformation and necrosis of the treated subpleural metastasis, accompanied by complete resolution of the pneumothorax. Although pneumothorax has been described as a rare and typically delayed complication of lung SBRT, its occurrence during the active course of treatment is exceptionally uncommon. Whether the event in our patient resulted from rapid radiation-induced tumor necrosis, the subpleural location of the lesion, DIBH-related pleural stretch, or a combination of these mechanisms remains speculative. This case highlights the importance of vigilance for pneumothorax during SBRT for peripheral pulmonary metastases and illustrates that carefully selected asymptomatic patients may be managed conservatively with successful completion of treatment.