The HexaPODTM evo RT System allows for corrections in 6 degrees of freedom (DoF) (translations and rotations along each of the x-, y-, and z-axes). It has most commonly been used for stereotactic body radiotherapy (SBRT) treatments in combination with highly rigid immobilization to enhance the quality of image registrations. The purpose of this study is twofold: to determine whether the use of 6-DoF corrections will yield superior image registrations for conventionally-fractionated head and neck IMRT treatments with 0.5-cm PTV margins, and to determine a margin for such H&N treatments at which the use of 6-DoF corrections demonstrates significant registration improvements. Twenty patients retrospectively treated for H&N cancers were selected. A variety of H&N subsites were included, provided that the relevant treatment volumes included the primary tumours and lymph nodal groups. Patients were prescribed 60-70 Gy/30-35 # to the primary tumour, and 54-56 Gy to the nodal volumes; patients being treated with small treatment volumes (e.g., SBRT, early-stage glottic cancers) were excluded. Global cone beam CT (CBCT)-CT image registrations were performed by a single observer for 6 fractions per patient. The same observer produced contours for the clivus, C2 vertebra, C7 vertebra, and mandible for each patient. Uniform expansions (0.5-cm and 0.3-cm) of these sub-volumes were generated, and an acceptable sub-volume match for each margin was defined by the expansion contour's complete encapsulation, observed in all three spatial planes, of the pertinent structure on the secondary CBCT image. Acceptability was evaluated for each sub-volume, for both 0.5-cm and 0.3-cm margins, with 3- and 6-DoF corrections. For the 0.5-cm margin, the percentage of unacceptable registrations across all sub-volumes was 8% using 3-DoF corrections and 2% using 6-DoF corrections. This increases to 32% and 9%, respectively, for the registrations using the 0.3-cm uniform expansion margin. In both cases, the C7 vertebra shows the greatest improvement (43% of improved registrations for 0.3-cm, and 15% for 0.5-cm). C2 demonstrated the least impact of the 6-DoF corrections, with reductions of only 11% and 3% in unacceptable registrations for the 0.3-cm and 0.5-cm margins, respectively. There were no significant correlations seen in registration improvement with respect to treatment fraction. The improvement in using 6-DoF corrections for a 0.5-cm margin are not significant enough to warrant the consideration of implementing such a technique. The use of 6-DoF corrections in the case of a 0.3-cm margin proves to be beneficial, and such a margin has been demonstrated to be adequate for planning target volume coverage. This technique would be worth considering, if it resulted in no increased cost with regards to workflow, or in reduction of patient-related toxicities.