EGS5 Monte Carlo code is a general-purpose code for calculating photons and electrons transport for complex geometries in a wide range of energies. EGSnrc Monte Carlo code (BEAMnrc enclosed) was specially developed for medical physics usage, in particular for Linac modeling and dose calculations. Both EGS5 an EGSnrc were developed based on the former EGS4 code. For each of the codes, changes were made in the electron transport methods and in the geometrical utilities. Conformity between EGS5 calculation results and EGSnrc code results for Linac modelling was shown in recent work in our group. However, a large simulation run-time difference was found for the same conditions and statistical precision between these two codes. The EGS5 code took a longer period to obtain the same results compared to the EGSnrc code for Linac modelling. The electron transport in EGSnrc is based on the ESTEPE parameter, which is the maximum fractional energy loss per electron step. We investigated the ESTEPE parameter influence on the run-time and on the results accuracy. A set of variety simulations were performed using both codes in order to inspect the codes performance. We found that the EGSnrc run-time is strongly influenced by choosing different ESTEPE parameter values. While setting larger fractional energy losses per step, reduced simulation run-time was achieved. Hence, for optimal dose, one should define the optimal ESTEPE step-size parameter to achieve the desired dose results resolution. The use of the EGS5 code, based on the electron transport method improvements, is automatically adapted to the desired dose results quality without any user interference. Choosing the proper ESTEPE parameter for the use of EGSnrc for a given simulation resulted in similar run-time duration as with the use of EGS5. In conclusion, some cases that were tested in this study on the EGS5 and on the EGSnrc showed that the EGS5 is faster and more fluent to use between these two codes.
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