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.

Axxent Miniature X-ray Tube

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

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

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

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

Geant 4 Bremsstrahlung Production

Bremsstrahlung mean free path Bremsstrahlung angular distribution

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

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

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

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

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

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

Gaf EBT in Lucite: Relative Dose distribution at 1.5cm

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

Acknowledgement

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