Background/Aims: Assessment of system accuracy is a vital part of acceptance testing and commissioning for stereotactic radiosurgery/stereotactic radiotherapy (SRS/SRT). The accuracy of an integrated SRT system utilizing the TomoTherapy Hi-Art® system and the Medical Instrumentation and Diagnostics Corp. (MIDCO) BodyLoc whole-body stereotactic localizer was evaluated for the purpose of delivering conformal radiotherapy with non-invasive fixation for hypofractionated treatment regimens. Methods: Measurements of setup accuracy for image-guided radiation therapy (IGRT) of head and neck, prostate and brain treatments utilizing the MVCT image registration capability of the TomoTherapy system were individually assessed and compared to similar published data. Using Monte Carlo simulations, phantom positioning and phantom target studies, the BodyLoc’s imaging resolver was evaluated for its accuracy in stereotactic localization, patient positioning and dosimetric accuracy. Setup positioning accuracy for clinical cases utilizing different combinations of mask and posterior supports was evaluated using image guidance to establish an acceptable non-invasive fixation method. Results: Analysis of the TomoTherapy system clinical positioning data showed the mean three-dimensional positioning displacements for image-guided intensity modulated radiation therapy (IGRT) setups of the prostate, head and neck and brain treatments to be ± 9.8, ± 5.5 and ± 3.2 mm respectively. This compared favorably with published data for prostate and head and neck sites. A combination of a reinforced Aquaplast mask with a mouthpiece-type bite block along with a customizable posterior mold (Accuform) resulted in fixation which reduced the mean setup variation to ± 1.4 mm which is comparable to values of accuracy demonstrated by Galloway’s group [Biomed Instrum Technol 1991;25:457–460] and is slightly less than the voxel length of the reconstructed MVCT. The BodyLoc system’s imaging resolver was evaluated for accuracy at known QA marker levels within the system. The calculation accuracy was confirmed at the 100-, 300-, 500-, 700- and 900-mm QA marker Z ordinate levels within the frame to be within ± 0.5 mm. The combined system dosimetric accuracy was measured with film and, through profile analysis, was shown to be ± 0.6 mm. Conclusion: The combination of the BodyLoc system’s high-resolution imaging resolver for stereotactic localization and immobilization along with the TomoTherapy’s MVCT image guidance and helical treatment delivery, results in positioning accuracy acceptable for SRT and select SRS cases. This result was shown to be less than the length of the MVCT voxel (sub-voxel accuracy) despite signifi cant partial volume effects in the longitudinal dimension. As demonstrated by the results of the HexaPhant® accuracy test (HAT), the dosimetric accuracy of the combined delivery system is within the values recommended in the ACR practice guidelines of ± 1 mm for intracranial treatments and ± 2 mm for extracranial applications. The integrated SRS/SRT system consisting of the TomoTherapy Hi-Art, Philips AcQSim/Pinnacle3® treatment planning system and the MIDCO BodyLoc system has been combined to be a fully acceptable system.