Following partial mastectomy for right-sided breast cancer, a 47-year-old female received a radiation dosage of 50 Gy to the right breast using the linear acceleration (linac)-based system. Five months later, she developed a fever and cough. High-resolution computed tomography (CT) images showed irregular bilateral pulmonary infiltrates. Oral corticosteroid medication was started for radiation pneumonitis, which disappeared rapidly. During administration of the low-dose step-down protocol for oral corticosteroids, pulmonary infiltrates reemerged twice. At the second reemergence, 18 spherical nodules with the reversed halo sign appeared on both lungs which constituted histologically proven organizing pneumonia. Two months later, they had all disappeared. Dynamic analysis over time of the change in size of the spherical nodules showed that each nodule ballooned to reach its maximal size and then disappeared. This case suggests that radiation-induced organizing pneumonias each follow a similar pattern of resolution.