The Depth of the Spinal Cord below the Skin

When X-ray therapy is planned to the spinal cord and to the bodies of the vertebrae it is sometimes difficult to estimate the depth at which the dose should be prescribed as the depths of vertebrae vary throughout the length of the spinal column. A series of measurements of these depths has been made and the following tables compiled. When curative radiotherapy of neoplastic disease is being planned it is essential that the appropriate measurements be determined in the individual patient. However, on many occasions palliative radiotherapy is given to the spine and the measurements given in this paper may be a useful reference when prescribing such treatment. The measurements were taken from X-ray films of adult myelograms, and also from adult lateral chest films. From 197 adult myelograms analysed a number were selected for measurement where the quality was such that the skin, spinous processes, the anterior contour of the Mvodil column and the posterior surface of the vertebral bodies were clearly seen in the lateral projection. In the upper dorsal region the location of the skin relative to the tips of the thoracic spinous processes was considered to be not accurate enough to be measured by this method. In some cases this was due to penetrationof soft tissues by a beam of the quality required for outlining bone and Myodil and in other cases there was an overlap of scapula and soft tissues which made the position of the soft tissue over the spine indeterminate.