Abstract: Radiotherapy plays a significant role in the treatment of lung malignant tumor. However, as the most main complication of radiotherapy used to treat lung malignant tumor, radiationinduced lung injury is an important influencing factor in impeding further and higher dose radiotherapy. Previous studies show that mesenchymal stem cells (MSCs) have the characteristics of selfreplication, multiple differentiation, immunoregulation and directional migration. MSCs can help to repair many kinds of acute and chronic lung injury, meanwhile stem cell transplantation stimulates production of many cytokines to attenuate acute lung injury. So stem cell therapy provides a new kind of thinking in the prevention and treatment of radiationinduced lung injury. 

Key words: Mesenchymal stem cells, Radiation pneumonitis, Cytokines