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Calculations of electron fluence correction factors using the Monte Carlo code PENELOPE
E A Siegbahn1, B Nilsson, J M Fernández-Varea
1Department of Medical Radiation Physics, Karolinska Institutet and Stockholm University, Box 260, S-171 76 Stockholm, Sweden. albert.siegbahn@ks.se
Physics in Medicine and Biology
|June 19, 2003
Summary
Electron beam dosimetry requires a correction factor (phi(water)plastic) when using plastic phantoms instead of water. New Monte Carlo simulations show these factors differ from current recommendations, especially at greater depths.
Area of Science:
- Medical Physics
- Radiation Dosimetry
- Computational Physics
Background:
- Plastic phantoms are used in electron-beam dosimetry as water substitutes.
- A fluence correction factor, phi(water)plastic, is necessary for accurate dose determination.
- Existing recommendations for phi(water)plastic from AAPM and IAEA show discrepancies, particularly at deeper levels.
Purpose of the Study:
- To calculate electron fluence correction factors (phi(water)plastic) using Monte Carlo simulations.
- To compare simulated phi(water)plastic values with existing AAPM and IAEA recommendations.
- To investigate the reasons for discrepancies in phi(water)plastic values.
Main Methods:
- Utilized the PENELOPE Monte Carlo code for electron fluence calculations.
- Simulated semi-infinite phantoms of water and various plastic materials (PMMA, polystyrene, A-150, polyethylene, Plastic water, Solid water).
- Employed monoenergetic electron beams (6, 10, 20 MeV) and a realistic clinical beam.
Main Results:
- Simulated phi(water)plastic factors deviated from AAPM and IAEA recommendations by up to 2%.
- Calculated factors showed better agreement with previous EGS4 simulations and experimental measurements using an ion chamber.
- Identified an interdependence between depth-scaling and fluence-scaling corrections as a potential source of discrepancy.
Conclusions:
- Monte Carlo simulations provide more accurate phi(water)plastic values than current recommendations.
- Discrepancies in phi(water)plastic can be attributed to differing depth-scaling rules.
- Further investigation into depth-scaling is crucial for improving electron-beam dosimetry accuracy with plastic phantoms.