The angular and energy distribution of the primary electron beam

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Accurate modeling of electron beam angular distributions is crucial for radiation therapy treatment planning.
• Siemens KD-2 linear accelerator electron beams require precise characterization for clinical application.

Purpose of the Study:

• To determine the angular distribution of electron beams from a Siemens KD-2 linear accelerator.
• To compare Fermi-Eyges multiple Coulomb scattering calculations with EGS4 Monte Carlo simulations for electron transport.
• To validate the use of Gaussian approximations for incident angular distributions in treatment planning.

Main Methods:

• Simulated electron transport through scattering foils and air using Fermi-Eyges theory.
• Performed EGS4 Monte Carlo simulations of electron transport, incorporating Moliére theory and discrete interactions.
• Compared simulated angular distributions and standard deviations with experimental data.

Main Results:

• Both Fermi-Eyges and EGS4 simulations yielded similar angular distributions, closely matching experimental results.
• EGS4 simulations showed slightly non-Gaussian distributions due to Moliére theory and discrete interactions.
• Fermi-Eyges theory and Monte Carlo simulations predicted mean electron angles proportional to off-axis distance.

Conclusions:

• Gaussian approximation of incident angular distribution is adequate for treatment planning algorithms.
• Fermi-Eyges theory provides a viable alternative to experimental methods for determining angular standard deviation.
• Effective source positions derived from simulations closely matched experimental findings for a 15 MeV electron beam.