The battle against respiration-induced organ motion in external beam radiotherapy.

The latter 2 decades of the last century have witnessed significant improvements in external beam radiotherapy (EBRT), moved primarily by the advances in imaging modalities and computer-based treatment planning. These advancements lead to introducing the addition of a fourth-dimension, time, to the three-dimensional geometry in EBRT. The new era in EBRT presents challenges and opportunities to compensate for the effect of respiratory-induced target motion and improve treatment output. A number of these methods have been investigated, some of them already clinically approved and some still under development. Thus, there has been an increasing amount of literature in the area of respiratory motion compensation in EBRT. One criticism in most of the literature is that, it is either unorganized, or provides limited information. A few literature reviews provide a comprehensive overview regarding this fast growing area of study. The literature review here will provide an up to date summary of these publications.