CHAPTER 4
ELECTRON ABSORBED DOSE KERNELS TO ACCOUNT FOR SECONDARY PARTICLE
TRANSPORT INT DETERMINISTIC SIMULATIONS
In previous chapters, Charged Particle Equilibrium (CPE) and its limitations were
presented, and that in cases with high energy photons, corrections for secondary electron
transport may be significant. As mentioned, this is readily treated in Monte Carlo codes, yet quite
difficult to treat explicitly in deterministic codes due to the large electron ranges and added
numerical complexities in reaching convergence in photon-electron transport problems The
goal here is to produce a methodology to accurately estimate organ absorbed doses and attribute
whole body absorbed doses incurred from irradiations characteristic of external beam therapy
using the CT-based anatomical patient geometries in 3-D deterministic discrete ordinates (SN)
radiation transport models. Accurate absorbed doses will be rendered using pre-computed, high
resolution Monte Carlo based electron kernels. In doing so, the flux and the current provided by
the SN method will be used to both scale and project the absorbed dose using the Monte Carlo
based kernels, and map it to the surrounding voxels. Hence, this approach preserves high fidelity
and accuracy, accounting for complete photon transport, with the final absorbed dose delivered
from electron transport propagated by coupling with 3-D deterministic photon transport; this is
what makes this approach novel. In this chapter, water phantom results using a 0 to 8-MeV step
uniform beam will demonstrate that absorbed doses can be accurately obtained within the
uncertainties of a full physics Monte Carlo simulation.
4.1 Introduction to The EDK-SN Method
Various modalities are applied in absorbed dose calculations for high energy photon
beams, including empirical models that are based on measurements made in the clinic, Of
theoretically based models, such as the application of Monte Carlo techniques3'48. Alternatively,
as mentioned earlier, deterministic methods have been implemented to assess absorbed dose