ABSTRACT
Stereotactic body radiation therapy (SBRT) was possible prior to modern image guided radiation therapy (IGRT), but generally relied on an external frame or other coordinate systems, making this procedure time consuming and difficult. The choice of IGRT modality for SBRT depends on several factors including the radio-opacity of the lesion or its setup surrogate, the need to avoid nearby critical structures, the need to image with respect to time and respiration and, perhaps most importantly, the availability of equipment in the department. The entire SBRT treatment team including attending physician, physicist, therapist and dosimetrist must be full participants in the SBRT quality assurance program. The simulation approach most widely used for SBRT lung tumors is four-dimensional computed tomography (4D-CT) where the 4th dimension is respiratory phase. In 4D-CT a series of three-dimensional CT datasets are created each of which represents the patient's anatomy during a different breathing phase.
