Phase space evolution distribution functions for high energy electron beams

The phase space evolution (PSE) model is a 3D electron beam dose calculation model for radiation oncology. The PSE model is based upon the transport of electrons with a specific energy and direction over short distances (typically 0.3-1 cm). The result of the transport of these electrons is described by an energy and direction distribution of the electrons, which is stored in a database. The database is used by the PSE model at the time of the actual electron transport simulation. A good agreement between dose distributions calculated by the PSE model and EGS4 Monte Carlo code for mono-energetic, mono-directional electron beams was found. The differences in point dose are within 1-2% of the maximum dose. These differences can be caused by errors in the database used, or by assumptions made in the PSE model. The aim of this paper is to get more insight into the possible errors introduced by the database. Results show that the data in the database are in good agreement with EGS4 calculated data. Also the influence of the database on a PSE calculated dose distribution has been investigated. The differences between a PSE calculated dose distribution and an EGS4 calculated dose distribution can be reduced to < 0.5% if the database is replaced by a database partly created by EGS4. This shows that small errors in the database have a distinct effect on the dose distribution, and that this dose distribution can be calculated accurately by the PSE model if the right database is used. (author)