Calculating the angular standard deviation of electron beams using Fermi-Eyges theory

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• Accurate electron beam characterization is essential for precise radiation therapy dose calculations.
• The Hogstrom pencil beam method requires knowledge of electron beam angular distribution at the applicator face.
• Experimental measurement of penumbra width at various distances is a common method to determine angular spread.

Purpose of the Study:

• To theoretically calculate the angular standard deviation of electron beams using Fermi-Eyges theory.
• To compare theoretical calculations with experimentally derived angular spread values.
• To assess the utility of Fermi-Eyges theory for validating experimental data in radiation therapy.

Main Methods:

• Theoretical calculation of angular standard deviation using Fermi-Eyges theory, incorporating linear accelerator scattering foil geometry and composition.
• Experimental determination of angular spread through penumbra width measurements at multiple distances from the applicator face.
• Comparison of theoretical and experimental results for electron energies ranging from 6 to 21 MeV.

Main Results:

• Theoretical calculations of angular spread using Fermi-Eyges theory demonstrated strong agreement with experimental measurements.
• The agreement was within the experimental error for electron energies between 6 and 21 MeV.
• Fermi-Eyges calculations were found to be computationally fast.

Conclusions:

• Fermi-Eyges theory provides a reliable and efficient method for calculating electron beam angular spread.
• Theoretical validation using Fermi-Eyges theory can effectively complement experimental measurements.
• This approach enhances the accuracy and efficiency of beam definition for radiation therapy dose calculations.