Penumbra Width Determination of Single Beam and 201 Beams of Gamma Knife Machine Model 4C Using Monte Carlo Simulation Publisher



Mahmoudi A¹ ; Shirazi A¹ ; Geraily G¹ ; Hadisi Nia T¹ ; Bakhshi M¹ ; Maleki M² Show Affiliations
Source: Journal of Radiotherapy in Practice Published:2019

Abstract

Background One 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 materials In 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.Results Based 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 0·75, 0·77, 0·90 and 0·92 mm, respectively. The data for 201 beams obtained from simulation were 2·61, 4·80, 7·92 and 9·81 mm along X axis and 1·31, 1·60, 1·91 and 2·14 mm along Z axis and from film dosimetry were 3·21, 4·90, 8·00 and 10·61 mm along X axis and 1·22, 1·69, 2·01 and 2·25 mm along Z axis, respectively.Conclusion The 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. © 2018 Cambridge University Press.