Purpose: To achieve the best possible therapeutic ratio using image-guided radiation therapy (IGRT) of external beam radiation therapy in prostate cancer patients using kilo voltage cone-beam computed tomography (Kv-CBCT). Materials and methods: Thirty patients of carcinoma prostate who were treated with IGRT were included in the study. CBCT was done twice a week in IGRT. These images were registered with the planning CT scan images and translational error were applied and recorded and all 420 CBCT images were studied. The margins of planning target volume were calculated from the variation in setup. Results: The setup variation was 4.48, 5.18 and 8.03 mm in anteroposterior, mediolateral and superoinferior direction. This allowed adequate dose delivery to the clinical target volume and sparing of organ at risks. Conclusion: Kv-CBCT is a satisfactory method to accurate patient positioning in treating prostate cancers with high precision technique.