Radiosurgery Treatment Planning.

The Gamma Knife (Leksell Gamma Unit; Elekta Radiosurgery, Inc, Atlanta, GA) and specially adapted linear accelerators are the systems most commonly used for intracranial stereotactic external beam irradiation. Both systems deliver collimated radiation to a treatment isocenter and a stereotactic head frame is required to align each target or portion of the target with this isocenter. Image acquisition and treatment planning define how the target is to be treated using one or more treatment positions. Diagnostic images are required to link the target volume with the stereotactic frame coordinate system. The number of diagnostic imaging modalities and the corresponding diagnostic technique(s) selected for optimum target localization are determined by the nature of the target and surrounding structures. The diagnostic modalities presented in this article include magnetic resonance imaging, magnetic resonance angiography, computerized tomography, and x-ray angiography. This review covers the fundamentals of radiosurgical treatment planning using the Gamma Knife as the system of reference.