Close radiographic landmarks for spinal cord localization in treatment of thoracic malignancy.

BACKGROUND: On simulation radiographs of oblique fields, the spinal canal is estimated to be located on the deep surface of the tangential parts of the vertebral laminae within a width of the oblique diameter of the spinal canal. The aim of this study was to evaluate the accuracy of the estimated location of the spinal canal. MATERIALS AND METHODS: Beam's eye view digital simulation radiographs were produced using actual patient data from a computed tomography (CT) scanner. The spinal canal was projected onto the Beam's eye view image, and measurement of the distance between the tangential parts of the vertebral laminae and the anterior border of the spinal canal was performed. The oblique diameter on the axial CT image was compared to the measured distance. RESULTS: In all 10 patients, the tangential parts of the vertebral laminae were detectable on the Beam's eye view image. At all levels in all patients, the oblique diameter was slightly larger than or equal to the distance. With a gantry angle of 30 degrees the difference ranged from 0 to 2.5 mm (mean, 1.2 mm), from 0 to 1.0 mm (mean, 0.4 mm), and from 0 to 1.5 mm (mean, 0.4 mm) at levels T-1, T-4, and T-7, respectively. With a gantry angle of 45 degrees the difference ranged from 0 to 1.5 mm (mean, 0.8 mm), from 0 to 0.5 mm (mean, 0.3 mm), and from 0 to 1.0 mm (mean, 0.4 mm), respectively. CONCLUSION: The tangential parts of the vertebral laminae are useful landmarks, since the spinal canal location estimated using the tangential parts and measured oblique diameter of the spinal canal on the axial CT image is sufficiently accurate.