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The aim of this retrospective study was to investigate characteristics of organizing pneumonia (OP) after stereotactic body radiotherapy (SBRT) for lung tumor. Between September 2010 and June 2014, patients who were diagnosed as Stage I lung cancer and treated with SBRT at our institution were included in this study. A total of 78 patients (47 males with a median age of 80 years) were analyzed. The median follow-up period was 23 months. Five patients (6.4%) developed OP at 6–18 months after SBRT. The cumulative incidence of OP was 4.3% (95% confidence interval [CI], 1.1–11.0) and 8.2% (95% CI, 2.9–17.0) at 1 and 2 years, respectively. Tumor location (superior and middle lobe vs inferior lobe) was shown to be a borderline significant factor for the occurrence of OP (P = 0.069). In the subgroup analysis of patients with a radiographic follow-up period at least 6 months, or who died within 6 months after SBRT, 7 of 72 patients (9.7%) developed Grade 2 or 3 radiation pneumonitis (G2/3 RP) at 2–4 months after SBRT. A statistically significant association between G2/3 RP in the subacute phase and OP was shown (P = 0.040). In two of the five patients who developed OP, the symptoms and radiographic change were improved rapidly by corticosteroid administration. One patient had relapsed OP after suspending the treatment and re-administration was required. Three patients with minor symptoms were managed without corticosteroid administration and OP resolved without any relapse. The radiation-induced OP should be considered as one of the late lung injuries after SBRT for lung tumors.

A 41-year-old man with productive cough was admitted to our hospital. His chest roentgenogram showed multiple small nodules in the bilateral lung fields. The nodules were revealed as intrapulmonary metastases of the adenocarcinoma of the lung. Systemic chemotherapy with paclitaxel and carboplatin was not effective, and continuous oral gefitinib therapy was initiated. Twentyone days later, spontaneous pneumothorax was found in the left lung, and four days after that, in the right lung as well. The extent of the pneumothorax was slight; therefore, he recovered without drainage within several days. Spontaneous pneumothorax, especially bilateral pneumothorax, is a rare complication of chemotherapy for lung cancer.

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