  This study analyses the dose difference for a variety of phantom materials
that can be used for Leksell Gamma Knife. These materials have properties that
are very similar to the human tissue not including the skull bone. Geant4 was
employed in the analysis the dose distributions for collimator helmet sizes of
4mm and 8mm. The phantom had a radius of 80mm. Water, brain, PMMA (Poly-methyl
methacrylate) and polystyrene were used as the material types. Results showed
no considerable differences for radiation dosimetries depending on the material
types. In addition, the polystyrene and PMMA (Poly-methyl methacrylate) phantom
are also suitable for measuring the dose profiles of the Gamma Knife unit.
