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Dose calculation for electron therapy using an improved LBR method
Wondesen T Gebreamlak1, David J Tedeschi, Hassaan A Alkhatib
1Department of Physics and Astronomy, University of South Carolina, Columbia, South Carolina 29208, USA.
Medical Physics
|July 5, 2013
Summary
This study introduces a modified lateral build-up ratio (LBR) method to accurately calculate percentage depth dose (PDD) for irregular electron beams. The lateral spread parameter (σR(z)) was found to increase linearly with cutout size, improving PDD calculations.
Area of Science:
- Medical Physics
- Radiation Oncology
- Radiotherapy Physics
Background:
- Accurate calculation of percentage depth dose (PDD) is crucial for effective radiotherapy planning.
- Electron beam therapy requires precise dose calculations, especially for irregularly shaped fields.
- Existing methods may have limitations in predicting PDD for non-standard beam shapes.
Purpose of the Study:
- To develop and validate a modified lateral build-up ratio (LBR) method for calculating PDD of irregularly shaped electron beams.
- To investigate the relationship between the lateral spread parameter (σR(z)) and cutout size in electron beams.
- To assess the accuracy of the proposed method by comparing calculated PDDs with measured data.
Main Methods:
- Measured PDD curves for 6, 9, 12, and 15 MeV electron beams with various applicator cone and cutout sizes.
- Calculated LBR using measured PDD data and a reference open field.
- Determined the lateral spread parameter (σR(z)) from LBR and circular cutout radii.
- Calculated PDDs for irregular cutouts using the derived σR(z) characteristics.
- Compared calculated PDDs with measured PDDs for validation.
Main Results:
- The lateral spread parameter (σR(z)) was found to increase linearly with circular cutout size (R).
- This linear relationship was observed up to the equilibrium range of the electron beam.
- Calculated PDD curves for irregularly shaped cutouts showed high agreement with measured data.
- The percentage difference between calculated and measured PDDs was less than 1.0% within the therapeutic range.
Conclusions:
- The lateral spread parameter (σR(z)) is dependent on cutout size, contrary to common assumptions.
- The modified LBR method accurately predicts PDD for irregularly shaped electron beams.
- The findings are applicable across multiple electron beam energies (6-15 MeV).
- This method offers improved accuracy for radiotherapy dose calculations with irregular electron fields.
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