Objective The aim of this study was to optimize the 3D image (or Cone Beam Tomography Compute) acquisition protocols set by default by Elekta for their kV imaging system XVI in order to obtain the best compromise between the image quality, the delivered dose and the repositioning quality obtained for several radiotherapy localizations (head and neck, thorax, abdomen, pelvis and prostate). Materials and methods The study was conducted in three stages. As a first step, the image quality has been evaluated by changing the following parameters (kV, mAs, etc.). As a second step, the dose delivered for each acquisition protocols was studied. And finally, the positioning offsets proposed by the software, according to each XVI acquisition protocols, were evaluated. The results were compared to select the protocols offering the best compromise between image quality, delivered dose repositioning quality for each localization. Three types of dummys were used to conduct this study: Caphan® 600 for the image quality quantification, two PMMA dummy (32 and 16 cm in diameter) with two ionization chambers (10 cm pencil chamber and 0.6 cc farmer chamber) for dose measurements, and the anthropomorphic dummy Rando® for assessing the repositioning quality proposed by Elekta XVI software. Results For each localization studied, two protocols were identified by comparing their images qualities to those predefined in Elekta protocols. Dose measurements were validated by comparing the values obtained with the 10 cm pencil chamber and those obtained with the 0.6 cc farmer chamber (the maximum deviation of dose obtained is 1.13% between the two rooms). Obtained measurements are in agreement with the data described in the literature [Renstrom et al. 2005, Falco et al. 2010] as well as those provided by Elekta [Elekta XVI datasheet 2009] (the maximum difference in dose received was 1.04%). Doses obtained with optimized protocols IGRT are 5.8 mGy and 9.9 mGy for both M10 prostate protocols of 14 mGy and 16 mGy, for both M20 thorax protocols (same as abdominal and pelvic locations) 6.1 mGy and 12.3 mGy and for both S20 head and neck protocols. The average repositioning errors calculated by the XVI software, with the optimized protocols, were estimated and compared with reference values obtained with the default manufacturer protocols. For patient repositioning inferior to 1 cm, arround 1 mm error was found. However a maximum error up to 3.4 mm was found for patient repositioning greater than 1 cm. Conclusion Implementation of new protocols has reduced the dose delivered during image acquisition for patient repositioning under linear accelerator, while maintaining a very good image quality and an accurate patient shift estimation. Used in clinical routine, those new imaging protocols have contributed to define a new patient management in the radiotherapy service (IGRT) of the Institut Paoli-Calmettes.