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Successful thoracic endovascular aneurysm repair (TEVAR) is contingent on seal and fixation of the proximal graft. The aortic arch has a wide range of anatomic variability, and understanding that anatomy may optimize device deployment. The purpose of this study was to assess aortic arch anatomic features that influence zones 2 and 3 TEVAR and specifically to quantitate the impact of gantry angle correction on proximal seal zone for patients with proximal descending thoracic aortic disease.Sixty patients with descending thoracic aortic pathology that would require TEVAR with a zone 2 or 3 deployment were evaluated. Demographic and imaging data were retrospectively reviewed. Computed tomography scans were evaluated using a 3-dimensional workstation for centerline and angle analyses. The optimal gantry angle was determined to be the orthogonal view of the leading (proximal) edge of the seal zone based on a manual adjusted centerline. Measurements were then taken of the seal zone at −10° and −20° from optimal view to assess the impact of imperfect gantry angle correction.The study included 38 men (63%) with a mean age of 66 years (range, 24-90 years). Thirty-eight (63%) required zone 2 deployment. Zone 2 seal zones were shorter and required less gantry angulation for an optimal view than were zone 3 seal zones. Incomplete gantry angle correction affected expected use of both zone 2 and 3 seal zones similarly. At 10° and 20° from optimal gantry angel, the loss in use of available seal zone length is estimated to be 2.4 ± 1.1 and 6.2 ± 2.3 mm, or 10% and 25%, respectively. These results were not different for men or women, nor were they influenced by age, sex, body mass index, height, or etiology of aortic pathology. Inner and outer curvature measurements differed by 80%. Only four patients (7%) had a zone 1 segment ≥ 5 mm in length.Optimal gantry angle correction should be the goal of any TEVAR procedure. Zone 2 seal zones require less gantry angulation than zone 3 seal zones by nearly 20°. This study shows that correction within 10° of optimal is unlikely to significantly impact successful seal and fixation for most patients. At 20°, however, substantial loss of seal zone can be expected. Measurements of the inner and outer curvature reveal different information about the distal arch and should be assessed individually. Zone 1 deployment rarely provides meaningful additional seal zone length.