A Software Toolkit for Multi-Image Registration and Segmentation in IGRT and ART

Introduction An essential step in radiation therapy is accurate three-dimensional segmentation of the target and organs at risk. Traditionally, this has been done by manual contouring on a slice-by-slice basis, but modern adaptive radiation therapy (ART) protocols can require segmentation of multiple daily images for each patient [1], increasing the pressure to develop automated methods for segmentation. Image guided radiation therapy (IGRT) also implies periodic 3D images taken at treatment time. Image registration may be used to align the target with its location in the planning image, and deformable registration can be used to place dose distributions from different days in a common “tissue-based” frame of reference so that the cumulative delivered dose can be assessed [2, 3]. Furthermore, deformable registration offers a potential solution to the problem of repeated daily segmentations, as image deformations can be applied to segmentations of the planning image to generate segmentations of the treatment image [4]. We have developed a new software tool for image analysis in radiation therapy bringing together research software for automatic and manual segmentation, and deformable and rigid registration, into a single usable package. The tool is designed with adaptive radiation therapy in mind. For manual segmentation, it extends functionality found in in the treatment planning system PlanUNC [5]. In turn, the segmentation component of PlanUNC was a development of two earlier tools, IMEX [6] and MASK [7]. For automatic segmentation, the new tool permits two approaches. One approach relies on fitting a model called an m-rep to an image [8], and the other relies on deformable image registration [9]. A view of the main window is shown in Figure 1.