4D IMRT delivery

Increased interest in interventional strategies for managing respiratory motion in radiation treatments in recent years has been prompted by several factors. First, there has been limited ability to control tumors in the thorax and abdomen with standard radiotherapy techniques. Second, anatomical movement with respiration, at least in some circumstances, limits the accuracy with which radiation can be delivered to tumorbearing tissue. The resultant larger treatment volumes required to accommodate target mobility may limit the tumoricidal dose, owing to the larger amounts of surrounding normal tissue exposure, particularly for larger treatment volumes. Conversely, under-estimation of the required treatment margins may result in marginal misses. It therefore seems desirable to limit respiratory motion for tumor sites exhibiting large excursions. Third, technological advances have spawned new capabilities for measuring and reducing respiratory motion.