Positioning accuracy during VMAT of XXXX and the resulting dosimetric impact by a 6-degree-of-freedom couch in combination with daily kilovoltage cone beam computed tomography.

@entity5 @entity1 @entity50741
BACKGROUND: To improve the delivery of radiotherapy in @entity5 and to minimize the irradiation of unaffected tissues by using daily kilovoltage cone beam computed tomography (kV-CBCT) to reduce setup errors. METHODS: Thirteen @entity1 with gynecologic @entity5 were treated with postoperative volumetric-modulated arc therapy (VMAT). All @entity1 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 ( @entity50741 ) 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 @entity50741 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 @entity5 , reducing the @entity50741 . The reduced margin size permits improved normal tissue sparing and a smaller total irradiated volume.
