Advances in radiotherapy treatment planning led to improved local tumor control and better healthy tissues sparing. Without image guidance at the time of therapy (IGRT), changes in position, shape and intra-fractional motions may prevent desired dose from being precisely delivered to the planning target. The rapid fall-off in dose outside the target in highly conformal radiotherapy techniques impose demand for accurate target localization at the time of the treatment to avoid underdosing of disease. Daily kV cone-beam computed tomography (CBCT) acquisition can provide accurate 3D volumetric patient's anatomy prior to every treatment fraction and it is suitable for adaptive corrections of treatment positioning variations. This study retrospectively assesses dose volume histograms (DVHs) with and without IGRT employing CBCT. We also report on additional radiation skin dose to patients during CBCT. Pre-treatment 3D imaging of 20 patients in treatment position was acquired using Pelvis CBCT protocol on on-board imaging (OBI) system (v. 1.4 Varian Medical Systems, Palo Alto) on a daily basis and twice a week for prostate and rectum cancer patients respectively. The obtained reconstructed CBCT images were co-registered with planning CT data using bony landmarks for rectal patients and prostate soft tissue visibility and prostate contours for prostate cancer patients. Obtained shifts were used in the Eclipse Treatment planning system to mimic the non-IGRT guided treatment. We calculated the dose distribution for original and simulated plan and obtained DVHs for targets and organs at risk were compared. Prior to CBCT scan, film pieces were taped on patient skin. Films were scanned before and after irradiation with the Epson Expression 10000XL document scanner in reflective mode. Response of the reference film dosimetry system was calibrated in terms of air kerma in air. Our preliminary results show small difference in PTV coverage for rectum patients with better sparing of the bladder in high dose region. For prostate patients, DVH of simulated plan shows 5% worse PTV coverage when compared to the original plan while the bladder sparing increases significantly. Measured anterior dose during CBCT amounts to 1.60 cGy in larger and up to 3.17 cGy in smaller patients, while the lateral dose ranges from 1.63 cGy in larger and up to 2.68 cGy in smaller patients. Our preliminary data indicate better sparing of bladder in high dose regions, and possible margin reduction for PTV definition if daily CBCT was used. This could lead to better tumor control and decrease NTCP, but the benefits must be weighted against the dose delivered to patients during CBCT.