Radiotherapy of mobile tumors

In this overview, we discuss some major issues related to the management of mobile tumors and gating in radiotherapy. For most types of organ motion, there are both interfraction and intrafraction components. For respiratory motion, the magnitudes of these 2 components can be comparable and therefore both should be handled carefully. The motion artifacts in computed tomography (CT) simulation are discussed and the 4-dimensional CT scan technique is recommended for treatment simulation of patients with mobile tumors. There are various methods for handling organ motion in treatment delivery. Caution should be exercised when using patient-specific motion information for treatment planning because motion characteristics may vary from the treatment simulation time to the treatment delivery sessions. Respiratory gating is potentially accurate, easy to implement, and may be widely adopted in clinical practice in the near future, if existing technical problems can be resolved.