Abstract: Objective To investigate the relation of V₂₀ and MLD to radiation-induced lung injury.Methods From Aug 2008 to Jun 2010，47 patients with lung cancer and met the study criteria were enrolled. All patients receive 3D conformal radiotherapy by 6MVX-ray，and the doses ranged between 50Gy to 70Gy. DVH was gained through 3-dimensional TPS. The radiation treatment planning was V₂₀ ≤ 30% and the spinal cord volume was≤45Gy. Radiation-induced lung injury was diagnosed based on contrasted CT combined with clinical symptoms，and the extent of injury was evaluated according to RTOG grading criteria.Results The total incidence of radiation-induced lung injury was 31.9% (15/47). While the incidence of lung injury was higher in the group of V₂₀＞25% (46.2%) than that in the group of V₂₀≤25% (14.3%，P＜0.05)The incidence of lung injury was lower in the group of MLD≤15Gy (14.3%) than that in the group of MLD＞15Gy (57.9%，P＜0.05).  Conclusion The radiation-induced lung injury related significantly to V₂₀ and MLD that could help to predict the injury.

Key words: Radiation-induced lung injury, Lung cancer, V20, MLD