Radiation-induced organizing pneumonia caused by carbon-ion radiotherapy for lung cancer.

Radiation-induced organizing pneumonia is a rare complication of radiation therapy for thoracic cancer. Carbon-ion radiotherapy, an emerging treatment modality for early-stage lung cancer treatment, can also cause lung injuries. However, as cases of radiation-induced organizing pneumonia caused by carbon-ion radiotherapy for lung cancer have not been reported, its clinical features remain unclear. A 69-year-old woman was referred to our hospital 11 months after being diagnosed with early lung cancer due to refractory pneumonitis induced by carbon-ion radiotherapy. She had developed fever and dyspnea 4 months after undergoing carbon-ion radiotherapy and was subsequently diagnosed with radiation pneumonitis. The administration of oral prednisolone resulted in improvement. However, she relapsed each time the dose of prednisolone was tapered. She was diagnosed with radiation-induced organizing pneumonia caused by carbon-ion radiotherapy for lung cancer based on the clinical course and the results of the examination performed at our hospital. An improvement was observed after administering methylprednisolone (1000 mg/d) for 3 days. The dose of oral prednisolone was slowly tapered over a period of ≥6 months with no relapse. Organizing pneumonia caused by carbon-ion radiotherapy for lung cancer is treatable with corticosteroids; however, tapering the dose of corticosteroids may lead to relapse.