Quality assurance procedures for stereotactic body radiation therapy.

Cranial stereotactic radiosurgery (SRS) and radiotherapy (SRT) are established treatment modalities. Initial implementations of these techniques rigidly attached frames to the patient's head for single-fraction treatments. The head frame accommodates an external fiducial marker system that is a reliable reference for targets within the cranium and accurately links the imaging equipment used for treatment planning to the treatment device. Fractionated SRT treatments use noninvasive "relocatable"-type head immobilization that fixes to the patient's head and face features. Clearly defined quality assurance (QA) procedures exist for both cranial SRS and SRT but are not as well developed for extracranial SRT. Procedures for demonstrating the geometric relationship between the planning imaging and treatment have to some degree copied the techniques used for intracranial stereotactic irradiation. However, there are some unique QA issues that are specific to extracranial irradiation. One major consideration is the large number of methodologies available for stereotactic body radiation therapy. In addition to the variety of integrated image-guided frameless systems, there are immobilization devices (called body frame systems) that use a fiducial reference system similar to the cranial devices. This article describes generic QA approaches that can be adapted to the various stereotactic body radiation therapy methodologies.