Using Monte Carlo program BEAMnrc to simulate Siemens accelerator 6 MV photon beam

using BEAMdp program to analyse the energy spectrum distribution and mean energy from phase space data of different field sizes

then building beam source

energy spectrum and mono-energy source

to use DOSXYZnrc program to calculate the dose deposition kernels at dmax in standard water phantom with different beam sources and make comparison with different dose deposition kernels.The results show that the dose difference using energy spectrum source is small

the maximum percentage dose discrepancy is 1.47%

but it is large using mono-energy source

which is 6.28%.The maximum dose difference for the kernels derived from energy spectrum source and mono-energy source of the same field is larger than 9%

up to 13.2%.Thus

dose deposition has dependence on photon energy

it can lead to larger errors only using mono-energy source because of the beam spectrum distribution of accelerator.A good method to calculate dose more accurately is to use deposition kernel of energy spectrum source.