COMPARISON OF EGS4 AND MCNP MONTE-CARLO CODES WHEN CALCULATING RADIOTHERAPY DEPTH DOSES

The Monte Carlo codes EGS4 and MCNP have been compared when calculatin g radiotherapy depth doses in water. The aims of the work were to stud y (i) the differences between calculated depth doses in water for a ra nge of monoenergetic photon energies and (ii) the relative efficiency of the two codes for different electron transport energy cut-offs. The depth doses from the two codes agree with each other within the stati stical uncertainties of the calculations (1-2%). The relative depth do ses also agree with data tabulated in the British Journal of Radiology Supplement 25. A discrepancy in the dose build-up region may by attri buted to the different electron transport algorithms used by EGS4 and MCNP. This discrepancy is considerably reduced when the improved elect ron transport routines are used in the latest (4B) version of MCNP. Ti ming calculations show that EGS4 is at least 50% faster than MCNP for the geometries used in the simulations.