ABSTRACT
This chapter discusses the principles and uses of deformable shape models (DSMs) for segmentation of anatomy in volume images for radiotherapy applications. DSMs are being actively investigated in many research laboratories, and advances continuously appear in the literature. Although a good bit of research has been aimed at radiation therapy applications, translation into commercial clinical systems has been modest. This chapter focuses on methods that have reached clinical or near-clinical use and mentions others in translation (Section 10.4). Other approaches in commercial products, particularly nonrigid registration, are fundamentally different. Registration methods rely on contours of the target organ, which may be thought of as an organ model, drawn in a reference or atlas image. The model, however, is embedded in the atlas image and deformed by the nonrigid registration process; it cannot be independently deformed to match the target organ and is of no use without the corresponding atlas image. Level sets have some properties in common with boundary representations discussed below and in Section 10.2. However, level sets are discussed in Chapter 14 and not mentioned further.
