Gamma Knife® stereotactic radiosurgery as a treatment for essential and parkinsonian tremor: long-term experience J.R. Pérez-Sánchez; R. Martínez-Álvarez; N.E. Martínez Moreno; C. Torres Diaz; G. Rey; I. Pareés; A. Del Barrio A.; J. Álvarez-Linera; M.M. Kurtis;