Biophysical Modeling of Respiratory Organ Motion

Methods to estimate respiratory organ motion can be divided into two groups: biophysical modeling and image registration. In image registration, motion fields are directly extracted from 4D ( =3D+t) image sequences, often without concerning knowledge about anatomy and physiology in detail. In contrast, biophysical approaches aim at identification of anatomical and physiological aspects of breathing dynamics that are to be modeled. In the context of radiation therapy, biophysical modeling of respiratory organ motion commonly refers to the framework of continuum mechanics and elasticity theory, respectively. Underlying ideas and corresponding boundary value problems of those approaches are described in this chapter, along with a brief comparison to image registration-based motion field estimation.