Penumbra width determination of single beam and 201 beams of Gamma Knife machine model 4C using Monte Carlo simulation

Abstract

BackgroundOne of the stereotactic radiosurgery techniques is Gamma Knife radiosurgery, in which intracranial lesions that are inaccessible or inappropriate for surgery are treated using 201 cobalt-60 sources in one treatment session. In this conformal technique, the penumbra width, which results in out-of-field dose in tumour-adjacent normal tissues should be determined accurately. The aim of this study is to calculate the penumbra widths of single and 201 beams for different collimator sizes of Gamma Knife machine model 4C using EGSnrc/BEAMnrc Monte Carlo simulation code and comparison the results with EBT3 film dosimetry data.Methods and materialsIn this study, simulation of Gamma Knife machine model 4C was performed based on the Monte Carlo codes of EGSnrc/BEAMnrc. To investigate the physical penumbra width (80-20), the single beam and 201 beams profiles were obtained using EGSnrc/DOSXYZnrc code and EBT3 films located at isocentre point in a spherical Plexiglas head phantom.ResultsBased on the results, the single beam penumbra widths obtained from simulation data for 4, 8, 14 and 18 mm collimator sizes along X axis were 075, 077, 090 and 092 mm, respectively. The data for 201 beams obtained from simulation were 261, 480, 792 and 981 mm along X axis and 131, 160, 191 and 214 mm along Z axis and from film dosimetry were 321, 490, 800 and 1061 mm along X axis and 122, 169, 201 and 225 mm along Z axis, respectively.ConclusionThe differences between measured and simulated penumbra widths are in an acceptable range. However, for more precise measurement in the penumbra region in which dose gradient is high, Monte Carlo simulation is recommended.