ABSTRACT
Several techniques for both patient immobilization and image guidance have been developed that make hypofractionation on the Gamma Knife possible without compromising the historic precision characteristic of GKRS. This chapter explores the technology of frameless image-guided hypofractionated stereotactic radiotherapy using the Gamma Knife Perfexion with the Extend™ system (Elekta Instrument AB, Stockholm, Sweden), as well as the Gamma Knife Icon, with a focus on the technology of each system, the benefits and limitations, and the flexibility in workflow that each system supports. For the single-fraction case, the “gold standard” assumption has been that the rigid stereotactic frame provides superior immobilization performance over the relatively short time-frame required to deliver a radiosurgical treatment. Given the small geometric distances between tumor and sensitive organs at risk in the brain, any image-guided hypofractionated stereotactic radiation therapy system cannot deviate far from the single-fraction standard.
