Geant4 Monte Carlo Characterization of Novel Electronic Brachytherapy System

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Geant4 Monte Carlo Characterization of Novel
Electronic Brachytherapy System

• Derek Liu
• E. Poon, M. Bazalova, B. Reniers, M. Evans
• J. Seuntjens, T. Rusch, F. Verhaegen
• McGill University
• Xoft, Inc.

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Axxent Miniature X-ray Tube
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Project Objectives

• Characterize x-ray tube
• Monte Carlo with experimental verification
• Beam quality
• HVL
• Attenuation curve
• Photon Spectrum
• Spectrum
• 2-D Dose distribution
• Gafchromic film in Lucite Phantom

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Attenuation Curve

• NE 2571 farmer
• 2 mm Pb collimator
• 0.5 cm aperture

• Src-collimator 1
• Src-Al foil 2
• Src-detector 10

• Output fluctuation

Output monitor

• Beam hardening

Chamber response

• Scatter

Subtract scatter
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Spectrum

• Amp-Tek CdTe
• 1 mm Crystal
• 4 mil Be Window
• 2 mm W collimator
• 2 mm aperture

• Src-CdTe 1.5 m

• Air attenuation

Attenuation correction

• Detector response

Stripping procedure

• Energy Calibration

31.0 keV Ba-133 decay 14.9 keV Yttrium K-alpha
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Geant 4.8.1

• Why use Geant?
• Complex geometry
• Low energy physics
• C
• Coding flexibility

• Geometry
• Tip thickness 0.2 mm
• Transmission Tungsten target thickness 0.7 um
• 2 mm water

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Geant 4 Bremsstrahlung Production
Bremsstrahlung mean free path
Bremsstrahlung angular distribution
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Geant 4 Bremsstrahlung Production
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Source to Source Variation
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Comparison between Measured Spectra and Geant
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Source to Source Variation
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Aging Effects
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2-D Dose Distribution

• Gafchromic EBT films
• Lucite Phantom

• Src parallel to film
• Src-film 1.5 cm
• Exposure time 5 min
• Max dose 5 Gy

• Calibration

Ir-192 calibrated in water

• Film scanning

Document scanner

• Image registration

Matlab correlation routine
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Gaf EBT in Lucite Relative Dose distribution at
1.5cm
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Conclusion

• Geant4 Bremsstrahlung production comparable with
  EGS
• Angular distribution
• Bremsstrahlung mean free path
• Bremsstrahlung spectrum
• Spectral measurements
• Spectra in agreement with Geant4
• Attenuation curve measurements
• HVL in agreement with spectral HVL and Geant4
• Observed factors affecting beam quality
• Source variation
• Aging effect
• Dose distribution measurements
• General agreement with Geant4
• Deviation in forward and aft directions

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Acknowledgement

• This project is partially funded by Xoft, Inc.
• CdTe spectrometer funded by Research Institute of
  MUHC