1. Geant4 in Brachytherapy
Brachytherapy: Brief Overview
Clinical applications
Basic research
Ultrafast & biology applications
Issues for the work group
Dr. Paul Gueye Hampton University
AAPM, Seattle, WA July 24-28, 2005

2. Brachytherapy: Overview
Brachy: Greek word for “short”
→ Fast (targeted) radiation treatment
→ Catheter-driven insertion system
→ breast, head, neck, colon, prostate, esophagus,
eyes etc.
Typical sources
Gamma & beta emitters
Small: few mm3
Geometry: cylindrical (Iridium-192, Palladium-103)
Dr. Paul Gueye Hampton University
AAPM, Seattle, WA July 24-28, 2005

3. Modeling of encapsulated 192Ir source (Courtesy of McGill University)
3.5 mm
5 mm
1.1 mm
2 m
0.6 mm
MicroSelectron Classic HDR source (part no )
Dr. Paul Gueye Hampton University
AAPM, Seattle, WA July 24-28, 2005

4. G4NAMU @ AAPM, Seattle, WA July 24-28, 2005
Radial dose and anisotropy functions of encapsulated source (Courtesy of McGill University)
Anisotropy function
GEANT4:
±1% agreement with Williamson and Li
Radial dose function
GEANT4:
~0.4% higher than Williamson and Li (Med. Phys. 22, , 1995)
Dr. Paul Gueye Hampton University
AAPM, Seattle, WA July 24-28, 2005

5. Modeling of rectal applicator (Courtesy of McGill University)
made of silicone rubber
allows for insertion of
shielding materials
We collect phase space files of photons reaching the applicator surface and use the data for dose calculations in patient geometry.
Dr. Paul Gueye Hampton University
AAPM, Seattle, WA July 24-28, 2005

6. Isodose distributions (Courtesy of McGill University)
Presence of lead shielding reduces the dose distribution in a lucite phantom by up to 20%, and it is confirmed by ion chamber measurements.
Dr. Paul Gueye Hampton University
AAPM, Seattle, WA July 24-28, 2005

7. G4NAMU @ AAPM, Seattle, WA July 24-28, 2005
Octree geometry compression – DICOM images
Voxel-based geometry
Objectives:
Reduce the number of voxels
Keep the critical information
Indexing of the density distributions using a density gradient threshold:
High resolution kept only in heterogeneous area
Can easily reduce the number of voxels by 75%
Does not affect dose distribution
V. Hubert-Tremblay, MSc project
Dr. Paul Gueye Hampton University
AAPM, Seattle, WA July 24-28, 2005

8. G4NAMU @ AAPM, Seattle, WA July 24-28, 2005
Octree geometry compression – DICOM images
Examples: CT phantom + thorax patient
Voxel number v/s DGT
Dr. Paul Gueye Hampton University
AAPM, Seattle, WA July 24-28, 2005

9. Prostate brachytherapy - LDR
LDR 125I source, Amersham 6711
Validation of the model:
radial dose fonction
J.-F. Carrier, Ph.D. project
Dr. Paul Gueye Hampton University
AAPM, Seattle, WA July 24-28, 2005

10. G4NAMU @ AAPM, Seattle, WA July 24-28, 2005
Prostate brachytherapy - LDR
MC simulations on clinical treatment plans
RED PLAN
77 seeds
0.6 mCi activity
1.7% of the D90 value is lost due to interseed attenuation
1) Interseed attenuation
1.7%
3.3%
BLUE PLAN
137 seeds
0.3 mCi activity
3.3% of the D90 value is lost due to interseed attenuation
This interseed attenuation is not considered in TG43 (clinical) dose calculations
Dr. Paul Gueye Hampton University
AAPM, Seattle, WA July 24-28, 2005

11. G4NAMU @ AAPM, Seattle, WA July 24-28, 2005
Prostate brachytherapy - LDR
MC simulations on clinical treatment plans
2) Medium composition: CT-based MC
G4 DICOM reader[1]
Organ contours
Seed positions
CT image
G4 geometry
D90: 5-7% differences between water MC and CT-based MC
[1]
Dr. Paul Gueye Hampton University
AAPM, Seattle, WA July 24-28, 2005

12. Hampton University (Collaboration: NIST, EVMS)1 z 32
Scintillating Fiber based Beta Detector
→ Absolute calibration of sources
Lawrence Tynes, Ph.D.: Detector
Nnenna Onumah, Ph.D.: Geant4 z y
Dr. Paul Gueye Hampton University
AAPM, Seattle, WA July 24-28, 2005

13. Hampton University (Collaboration: Proxima Therapeutics, dePaul)
Active Mammosite
→ Absolute real-time position measurement (within ±1 mm)
→ Absolute real-time dose measurement
→ Modelization of the dose distribution using CT scan data
& 4D phantom
Jacquelyn Winston, M.Sc.: Detector
Rachel Black, Ph.D. : Detector, Geant4 & VTK
Dr. Paul Gueye Hampton University
AAPM, Seattle, WA July 24-28, 2005

14. Hampton University (Collaboration: Jefferson Lab, EVMS, ODU)
Breast cancer cells
Collimator and Sr-90 source
Dipole
Monoenergetic Brachytherapy Sources
→ Energy dependence of irradiated
breast cancer cells
Ariano Munden, M.Sc.
Dr. Paul Gueye Hampton University
AAPM, Seattle, WA July 24-28, 2005

15. ALLS Facility Ultrafast Laser & Biomedical Research
10 Hz, 300 mJ, 25 fs
Advanced Laser Light Source
Varennes, Canada
Dynamics of biological processes
100 Hz, 100 mJ, 25 fs
Dr. Paul Gueye Hampton University
AAPM, Seattle, WA July 24-28, 2005

16. Issues for the Working Group
Physics
Electromagnetic shower
Multiple scattering
Experimental cross sections (JLab data, others)
Theory (?)
Treatment verification
Bench marks
Examples
Micro-dosimmetry
Simulation at molecular level
Mono-energetic dose distribution
Other topics
Group organization
Therapy Physics (I. Chetty, MC in Treatment Planning)
Where to go from here?
To be discussed!!!
Dr. Paul Gueye Hampton University
AAPM, Seattle, WA July 24-28, 2005

17. G4NAMU @ AAPM, Seattle, WA July 24-28, 2005
Prostate brachytherapy - HDR
HDR 192Ir source, MicroSelectron
Preliminary results
Ejection spectrum
keV
A. Allard, Summer Project
Dr. Paul Gueye Hampton University
AAPM, Seattle, WA July 24-28, 2005