OBJECTIVE: The objective of this study is to introduce a new radiosurgical device, the Leksell Gamma Knife Perfexion (Elekta Instruments AB, Stockholm, Sweden). Design and performance characteristics are compared with previous models of the gamma knife in a clinical setting. METHODS: Performance-related features in the design of the new radiosurgical system are described, and the ability to create complex shapes of isodose volumes even with a single isocenter is demonstrated. The concept of "dynamic shaping" of dose distribution is introduced as a means of decreasing the exposure to structures outside the target. Dose plans for the Leksell Gamma Knife Models B, 4C, and Perfexion have been created for target pathologies to illustrate how the software and hardware of the new radiosurgical system can increase treatment quality, decrease treatment time, and increase patient comfort. Radiation doses to critical organs in the rest of the human body are compared. RESULTS: The automated collimator arrangement in the Perfexion makes it possible to produce more complex treatment volumes than with previous models of the gamma knife. This results from the enhanced ability to shape isodose volumes, even for single isocenters. The collimator arrangement and the patient positioning system also allow shorter patient transit times, reducing unwanted radiation exposure during movement between isocenters. CONCLUSION: The Perfexion exceeds the capabilities of previous gamma knife models in terms of treatment efficiency, conformity, and radiation protection. These qualities enable treatment of larger target volumes, especially close to eloquent areas. Pathologies previously inaccessible in the head and neck are now treatable due to the increased volume of the radiation cavity.