ABSTRACT
It might be reasonably argued that, provided the PTV is clearly established through such imaging techniques (and it is recognized that there are still signicant unknowns in terms of tumor and normal-tissue function), the delivery of CFRT and specically IMRT to static targets can be understood well from both a planning and delivery viewpoint. If the target does not change day to day, if the patient is set up the same way each day, and if the target does not move during the treatment, tailoring a high-dose volume to the PTV will be at the limit of what is possible, subject to the laws of the physics of photon-tissue interactions. None of these three provisos are, however, strictly possible. Dealing with the rst two problems is a eld outside the scope of this book [see review by Webb (2006c)]. Dealing with the last of them, the so-called intrafraction motion, is the subject of this book. In this chapter, we shall introduce the problem and some techniques for solving it using the tracking of the multileaf collimator (MLC) attached to the linac.
