Background: To improve the delivery of radiotherapy in gynecologic malignancies and to minimize the irradiation of unaffected tissues by using daily kilovoltage cone beam computed tomography (kV-CBCT) to reduce setup errors.Methods: Thirteen patients with gynecologic cancers were treated with postoperative volumetric-modulated arc therapy (VMAT).All patients had a planning CT scan and daily CBCT during treatment.Automatic bone anatomy matching was used to determine initial inter-fraction positioning error.Positional correction on a six-degrees-of-freedom (6DoF) couch was followed by a second scan to calculate the residual inter-fraction error, and a post-treatment scan assessed intra-fraction motion.The margins of the planning target volume (MPTV) were calculated from these setup variations and the effect of margin size on normal tissue sparing was evaluated.Results: In total, 573 CBCT scans were acquired.Mean absolute pre-/post-correction errors were obtained in all six planes.With 6DoF couch correction, the MpTV accounting for intra-fraction errors was reduced by 3.8-5.6 mm.This permitted a reduction in the maximum dose to the small intestine, bladder and femoral head (P=0.001, 0.035 and 0.032, respectively), the average dose to the rectum, small intestine, bladder and pelvic marrow (P=0.003, 0.000, 0.001 and 0.000, respectively) and markedly reduced irradiated normal tissue volumes.Conclusions: A 6DoF couch in combination with daily kV-CBCT can considerably improve positioning accuracy during VMAT treatment in gynecologic malignancies, reducing the MPTV.The reduced margin size permits improved normal tissue sparing and a smaller total irradiated volume.