Visualization and metabolic analysis of acute inflammation in the lung parenchyma plays a crucial role for the prediction and diagnosis of radiation-induced lung injury and is particularly important in medically inoperable patients because of a priori very limited pulmonary function. This case confirms that a radiation-induced lung injury is accompanied by acute inflammatory reaction in the lung parenchyma irradiated with a total dose of 12-40 Gy. This well-defined inflammation component could be exactly characterized with FDG-PET/CT.