geant4 monte carlo characterization of novel electronic brachytherapy system derek liu e. poon, m....
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Geant4 Monte Carlo Characterization of Novel Electronic Brachytherapy System
Derek LiuE. Poon, M. Bazalova, B. Reniers, M. Evans
J. Seuntjens, T. Rusch*, F. VerhaegenMcGill 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 Beam hardening Scatter
Output monitor
Chamber response
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 Detector response Energy Calibration
Attenuation correction
Stripping procedure
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
0.00E+00
5.00E-06
1.00E-05
1.50E-05
2.00E-05
0.00E+00 5.00E+00 1.00E+01 1.50E+01 2.00E+01 2.50E+01 3.00E+01 3.50E+01 4.00E+01 4.50E+01 5.00E+01
Energy (keV)
Ph
oto
n p
er in
cid
ent
par
ticl
e
Beam w/o eii Beam w/ eii G4 low energy G4 norm
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Source to Source Variation
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0 5 10 15 20 25 30 35 40 45 50
Energy (keV)
Ph
oto
n C
ou
nt
(no
rmal
ized
)
Src #1 Src #2 Src #3 Src #4
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Comparison between Measured Spectra and Geant
0
0.005
0.01
0.015
0.02
0.025
0.03
0 5 10 15 20 25 30 35 40 45 50
Energy (keV)
Ph
oto
n c
ou
nt
(no
rmal
ized
)
Averaged Measurements G4 Penelope G4 Low Energy
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Source to Source Variation
0.000
0.100
0.200
0.300
0.400
0.500
0.600
Src #1 Src #2 Src #3 Src #4 Geant4
HV
L (
mm
Al)
Spectrum Attenuation curve
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Aging Effects
0.000
0.100
0.200
0.300
0.400
0.500
0.600
Src #1 Src #2 Src #3 Src #4
HV
L (
mm
Al)
Fresh source Used source Old source
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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 Film scanning Image registration
Ir-192 calibrated in water
Document scanner
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