Optimized spinal cord contour propagation for fractionated radiation therapy planning

Abstract

An optimized contour propagation method for head-and-neck cases in fractionated radiation therapy is presented and three-dimensional displacements of the spinal cord are evaluated. Thirty-two planning CTs were acquired with either a Siemens Primatom or Toshiba Aquilion CT scanner. Each case comprises several control CTs acquired in treatment position by a Siemens Primatom CT-on-rails system. All manually segmented contours of the spinal cord were propagated from the planning CT to all subsequently acquired control CTs employing two-dimensional normalized cross-correlation. A multiplicity of non-rigid displacements is observed, even though head and thorax are tightly immobilized. An optimized configuration for the contour propagation method is derived. It turns out to reliably propagate manually segmented contours of the spinal cord. As a result, it can reveal insufficient external and internal rigid image matching and allows for its compensation. © 2009 Springer-Verlag.