The simulation combines data from many different sources, and uses many approximations. Thus all of the numbers need to be taken with a grain of salt
In general, technologists, physicists and physicians should use doses that are in the same range as their peers. The characterization of particular doses as acceptable or unacceptable is based on this principle, and the assessment of how well you have done is based on looking at the distribution in dose based on real data from a number of US and UK sources.