Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Radiation-induced lung injury is a general term for damage to the lungs which occurs as a result of exposure to ionizing radiation. In general terms, such damage is divided into early inflammatory damage (radiation pneumonitis) and later complications of chronic scarring (radiation fibrosis). Radiation-induced lung injury most commonly occurs as a result of radiation therapy administered to treat cancer. The lungs are the most radiosensitive organ, and radiation pneumonitis can occur leading to pulmonary insufficiency and death (100% after exposure to 50 gray of radiation), in a few months.