AbstractID: 8490 Title: Modeling the Electron Contamination in Clinical Photon Beams for Monte
Carlo Treatment Planning
The purpose of this work is to model the electron contamination in clinical photon
beam for Monte Carlo treatment planning and commission it using the measured
data. The electron contamination needs to be considered in Monte Carlo treatment
planning because its significant effects to the surface dose and the dose at the
shallow region. In this work, a planar source is used to represent the contaminant
electrons at the source plane (above the upper jaw). The energy spectrum of the
contamination electron is determined by the energy spectrum of the photon beam.
The relationship between them is being investigated based on the published and our
Monte Carlo simulation results for different linear accelerators and beams. The
intensity weight of the contamination electron source can be derived from the
difference of the dose at the build up region of the photon beam between the
measured results and the Monte Carlo results without considering the electron
contamination. During Monte Carlo dose calculation, we sample one point on the
source plane and one point on the sampling plane. The line connected the two point
defines the direction of the electron. This source model for electron contamination in
the photon beam is validated together with the source model for photon beam. The
dose distributions are compared with the measured data. Preliminary results show
good agreement (less than 2% or 2mm) for 6MV and 10MV photon beam from
Siemens Primus machine. The investigations for the different photon beams from
different machines are being carried out.