Abstract: Objective To investigate the impact of PET-CT on the clinical staging and target volume delineation of fused positron emission tomography（PET） and computed tomography（CT） images on the intensive modulated radiotherapy（IMRT） planning for the patients with local advanced non-small cell lung cancer（NSCLC）. Methods Thirteen patients with local advanced NSCLC were referred for IMRT.Each patient was underwent CT and PET scan for simulation plan in the same treatment position. PET images were co-registered CT images. The clinical staging of all patients was determined by PET-CT. Target volume delineation was initially performed on CT images and the corresponding PET data were subsequently used as an overlay to CT data to define the target volume by the same doctor. Two kinds of treatment plans were designed based on GTVCT and GTVPET-CT by the same physicist. The plan for each case was finished with 5 fields IMRT and given with a total dose of 60Gy at 2Gy per fraction. The following DVH parameters were evaluated. The indexes including V20， mean lung dose， mean dose to heart and the maximum dose to spinal cord were evaluated too. Results The clinical stages of five patients were changed by PET-CT image including 3 up-staged and 2 down-staged. Therefore， the management decision was modified in 1 patient. PET-CT image altered GTV and PTV： the mean GTV，PTV delineated on CT and PET-CT were 159.35±84.44cm3,442.12±172.57cm3 and 148.22±75.08cm3，428.64±157.91cm3 respectively. PET-CT image changed the parameters of DVH： the difference of indexes including V20，mean lung dose，mean dose to heart and the maximum dose to spinal cord between the two IMRT plannings were statistically significant. The plan based on the GTVPET-CT was proved to be better than it based on the GTVCT according to the DVH parameters. Conclusion PET-CT image fusion appeares to not only make the outlining of GTV accurate， but also have an advantage on dose-reduction of organ at risk in treatment planning for the patients with local advanced NSCLC.