Figure 2

55-year-old patient received irradiation in the whole left breast (50 Gy/25 fractions) with an electron boost (10 Gy/5 fractions) to the partial breast. The lung V20 was 6.0%. Four months after RT following breast-conserving surgery, a severe cough, fever and decreased oxygen saturation measured by a pulseoximeter (SpO2; 88% at room air) were observed. Pulmonary lesions outside the irradiated field were observed on chest radiographs, which were located in the bilateral lungs on CT. Prednisolone was started at 30 mg/day based on a diagnosis of BOOP syndrome. The prednisolone was gradually tapered off, because the symptoms and pulmonary lesions were improved. However, the pulmonary lesions appeared again at 6.5 months after RT without any symptoms. Prednisolone was again administered until 7.5 months after RT. Although the pulmonary lesions appeared again at 9.5 months after RT, there were no symptoms.