The integration of PET and CT scans allows the simultaneous use of biologic and anatomic imaging data for better delineating tumor and sparing normal critical structures. The aim of this study is to assess the impact on target volume delineation using CT vs. PETCT based plans, and to determine radiobiological effect on tumor and normal tissue by comparing Tumor control probability (TCP) & normal tissue complication probability (NTCP) of CT & PET-CT based plans. 15 patients of inoperable NSCLC planned for radical radiotherapy, underwent a planning CT scan of the thorax. Target volumes were contoured. Later PETCT images with the auto contoured MTV (Metabolic target volume) images, were fused with the planning CT images. Margins were similarly given to PETMTV for the generation of PET CTV and PET PTV. 3 Dimensional conformal radiotherapy (3DCRT) plans were made on the planning CT images and the planning PETCT images, and were compared dosimetrically and radio biologically. The study shows that the use of PETCT resulted in significant decrease in PETCT generated MTV versus GTV delineated on CT. Also, there was statistical significant decrease in the volume of the normal lung irradiated in terms of V40 and the MLD. TCP for PETCT based plans was significantly higher than that with CT based plans. Also, PETCT based planning resulted in a statistically significant decrease in the NTCP for lung and spinal cord. Therefore, the study concludes that incorporation of PETCT into radiotherapy planning of NSCLC is technically feasible and dosimetrically appealing strategy for patient treatment.