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Influence of source parameters on large-field electron beam profiles calculated using Monte Carlo methods.
Rebecca Weinberg1, John A Antolak, George Starkschall
1Department of Radiation Physics, The University of Texas M.D. Anderson Cancer Center, Houston, TX, USA. rweinberg@swmail.sw.org
Physics in Medicine and Biology
|December 17, 2008
Summary
This study improved Monte Carlo simulations for medical linear accelerator electron beams by using a divergent Gaussian source model. Adjusting the full-width at half-maximum (FWHM) parameter significantly reduced discrepancies in dose profiles, enhancing simulation accuracy.
Area of Science:
- Medical Physics
- Radiation Oncology
- Computational Dosimetry
Background:
- Previous Monte Carlo simulations for medical linear accelerator electron beams used a non-divergent Gaussian source.
- This model showed discrepancies in dose distributions for large fields without applicators, particularly in the profile shoulder region.
Purpose of the Study:
- To refine the source model for Monte Carlo simulations of medical linear accelerator electron beams.
- To improve the accuracy of calculated dose profiles by investigating a divergent Gaussian spatial distribution for the electron source.
Main Methods:
- The study implemented a divergent Gaussian spatial distribution for the electron source in Monte Carlo simulations.
- The full-width at half-maximum (FWHM) parameter of the source was systematically varied.
- The impact of FWHM on in-air fluence profiles, percent depth dose (PDD) profiles, and off-axis ratios (OARs) was evaluated at various source-to-surface distances (SSDs) and field sizes.
Main Results:
- Discrepancies in the shoulder region of a 6 MeV, 40x40 cm² off-axis ratio profile were reduced from 15% to 4% by using a FWHM of 0.45 cm.
- Optimal FWHM values were determined for various electron beam energies (e.g., 0.45 cm for 9 MeV, 0.22 cm for 12 MeV, 0.25 cm for 16 MeV, 0.2 cm for 20 MeV).
- The adjusted divergent Gaussian source model demonstrated improved agreement with measured data across multiple simulation geometries and SSDs.
Conclusions:
- A divergent Gaussian source model with optimized FWHM parameters significantly enhances the accuracy of Monte Carlo simulations for medical linear accelerator electron beams.
- The refined model provides better agreement with measured dose profiles, especially in challenging regions like the profile shoulders for large fields.
- This improved source model increases confidence in its application for diverse SSDs and field sizes in radiation therapy simulations.
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