The Next Challenge: Analysis of Motion in Radiotherapy

Abstract

It is beyond the scope of this book to offer a complete review on the subject of motion in radiotherapy, but we can provide an overview of the fundamental concepts regarding techniques in use. Treating tumors located in organs involves patient motion, and inter- and intra-fractional movement of the organ itself. These movements affect each other. Scattering or scanning beam treatment modes can be used with particle beams. In the case of scattering, the concepts and data are often based on clinical use, that is, procedures that are known and have been used in practice for many years. In the field of scanning, the research is based on the effect of interference countermeasures. Currently, offsetting the dosimetric influence of target movement, both inter- and intra-fractional, is still an area of research relevant to hadron therapy. In general, inter-fractional movement occurs on a scale of minutes to hours, while in general, intra-fractional movement occurs on a scale of seconds to minutes. Examples of targets that exhibit inter- and intra-fractional movement are lung, liver and prostate. In charged particle beam therapy, the established methods that are used in photon beam therapy are employed to address these movements. Whatever the technique used to deliver the radiation, the measurement of depth-dose is strongly influenced by target movement. The published data have covered the adverse effects regarding movement of the target, because they can lead to underdosing of the clinical target volume, even when field margins are used. For prostate treatment, intra-fractional movement is suppressed by means of dedicated immobilization, preventing the filling of the rectum and bladder by controlling drinking, or with enemas or a rectal balloon. The prostate moves more with a filled rectum than with an empty rectum. Inserting a balloon into the rectum, followed by inflation with saline solution, minimizes the amount of air in the rectum and distends its rear wall. The prostate also exhibits intrafractional motion [7]. Mayahara et al. [8], from the Hyogo Ion Beam Medical Center (HIBMC), instruct their patients to empty the bladder and rectum and do not use a rectal balloon for proton therapy.