Motion in radiotherapy: photon therapy.

This review considers the management of motion in photon radiation therapy. An overview is given of magnitudes and variability of motion of various structures and organs, and how the motion affects images by producing artifacts and blurring. Imaging of motion is described, including 4DCT and 4DPET. Techniques for monitoring motion in real time by use of surrogates are reviewed. Treatment planning for various motion-management treatment delivery strategies is discussed, including choice of planning image, treatment field margins and dose calculation. Imaging techniques displaying motion in the treatment room for pre-treatment as well as real-time imaging for localization and verification are covered, and their use for various motion-management treatment delivery techniques is discussed. Use of motion management for different treatment sites—breast, lung and other sites—is elaborated, and gating, breath-hold and beam tracking strategies are described. Suggestions are given for breast and lung for practicable protocols for routine clinical use of motion management, including decision strategies. Finally, a perspective of the future of motion management in photon radiation therapy is given.