Medical Physics for Leksell Radiosurgery

The ICON® Gamma Knife treatment unit is a modification of the Perfexion unit with the addition of a frameless-based treatment option and stereotactic cone-beam computed tomography (CBCT). The addition of infrared markers for the detection of patient motion and the use of a stereotactic CBCT revolutionizes how Gamma Knife procedures can be performed. A review of the basic medical physics concepts of the Gamma Knife unit is given. This includes a description of the cobalt-60 (60Co) sources and discussion of the interactions of gamma rays with matter, the dosimetric principles of 60Co, radiation protection principles, unit construction, absolute dose rate and relative output factor determination, radiologic focal point definition, and quality assurance needed to maintain proper functionality of the Gamma Knife unit. The new additions of the high-definition motion management and the stereotactic CBCT are discussed. A review of treatment planning metrics is given.