A critical evaluation of two methods of head fixation.

Two head-fixation systems, one using Thermoplast and the other Lightcast were tested as to reproducibility by comparing stereotactic coordinates before and after CT scan and after removal and reapplication of the helmets. Helmets constructed of Lightcast were more consistently stable than those constructed of Thermoplast probably due in part to the dental fixation used with the former. With Lightcast the change in position of coordinates was consistently less than 3 mm, i.e. 2 pixels, which is within the tolerance of the system as a whole.