geant4 in brachytherapy
DESCRIPTION
Geant4 in Brachytherapy. Brachytherapy: Brief Overview Clinical applications Basic research Ultrafast & biology applications Issues for the work group. Brachytherapy: Overview. Brachy : Greek word for “short” → Fast (targeted) radiation treatment → Catheter-driven insertion system - PowerPoint PPT PresentationTRANSCRIPT
Dr. Paul Gueye Hampton University
G4NAMU @ AAPM, Seattle, WA July 24-28, 2005
1
Geant4 in Brachytherapy
1. Brachytherapy: Brief Overview2. Clinical applications3. Basic research4. Ultrafast & biology applications5. Issues for the work group
Dr. Paul Gueye Hampton University
G4NAMU @ 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
G4NAMU @ 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. 080950)
Dr. Paul Gueye Hampton University
G4NAMU @ AAPM, Seattle, WA July 24-28, 2005
4
Radial dose and anisotropy functions of encapsulated source
(Courtesy of McGill University)
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
1.05
0 3 6 9 12 15radial distance (cm)
radi
al d
ose
func
tion
g(r)
GEANT4Williamson and Li
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
1.05
0 50 100 150angle (degree)
F (r
, the
ta)
r = 0.25 cm r = 0.5 cm
r = 1 cm r = 2 cm
r = 3 cm r = 5 cm
Radial dose functionGEANT4:~0.4% higher than Williamson and Li (Med. Phys. 22, 809-819, 1995)
Anisotropy functionGEANT4: ±1% agreement with Williamson and Li
Dr. Paul Gueye Hampton University
G4NAMU @ 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 materialsWe 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
G4NAMU @ 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
G4NAMU @ AAPM, Seattle, WA July 24-28, 2005
7
Octree geometry compression – DICOM imagesOctree geometry compression – DICOM images
• 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
Objectives:• Reduce the number of voxels• Keep the critical information
Voxel-based geometry
V. Hubert-Tremblay, MSc project
Dr. Paul Gueye Hampton University
G4NAMU @ AAPM, Seattle, WA July 24-28, 2005
8
Octree geometry compression – DICOM imagesOctree geometry compression – DICOM images
Examples: CT phantom + thorax patient
Voxel number v/s DGT
Dr. Paul Gueye Hampton University
G4NAMU @ AAPM, Seattle, WA July 24-28, 2005
9
LDR 125I source, Amersham 6711
Validation of the model:radial dose fonction
Prostate brachytherapy - LDRProstate brachytherapy - LDR
J.-F. Carrier, Ph.D. project
Dr. Paul Gueye Hampton University
G4NAMU @ AAPM, Seattle, WA July 24-28, 2005
10
This interseed attenuation is not considered in TG43 (clinical) dose calculations
MC simulations on clinical treatment plans
1) Interseed attenuation
1.7%
Prostate brachytherapy - LDRProstate brachytherapy - LDR
3.3%
RED PLAN77 seeds 0.6 mCi activity1.7% of the D90 value is lost due to interseed attenuation
BLUE PLAN137 seeds 0.3 mCi activity3.3% of the D90 value is lost due to interseed attenuation
Dr. Paul Gueye Hampton University
G4NAMU @ AAPM, Seattle, WA July 24-28, 2005
11
2) Medium composition: CT-based MC
Prostate brachytherapy - LDRProstate brachytherapy - LDR
CT image G4 geometry
G4 DICOM reader[1]Organ contoursSeed positions
[1] http://www.physmed.phy.ulaval.ca/phys_med/DICOM[1] http://www.physmed.phy.ulaval.ca/phys_med/DICOM
D90: 5-7% differences between water MC and CT-based MC
MC simulations on clinical treatment plans
Dr. Paul Gueye Hampton University
G4NAMU @ AAPM, Seattle, WA July 24-28, 2005
12
Hampton University(Collaboration: NIST, EVMS)
Scintillating Fiber based Beta Detector
→ Absolute calibration of sources
Lawrence Tynes, Ph.D.: Detector
Nnenna Onumah, Ph.D.: Geant4
z
y
1
z 32
Dr. Paul Gueye Hampton University
G4NAMU @ 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
G4NAMU @ AAPM, Seattle, WA July 24-28, 2005
14
Hampton University(Collaboration: Jefferson Lab, EVMS, ODU)
Monoenergetic Brachytherapy Sources
→ Energy dependence of irradiated
breast cancer cells
Ariano Munden, M.Sc.
Dipole
Breast cancer cellsCollimator and Sr-90 source
Dr. Paul Gueye Hampton University
G4NAMU @ AAPM, Seattle, WA July 24-28, 2005
15
ALLS FacilityUltrafast Laser & Biomedical Research
Advanced Laser Light Source– Varennes, Canada– Dynamics of biological processes
10 Hz, 300 mJ, 25 fs
100 Hz, 100 mJ, 25 fs
Dr. Paul Gueye Hampton University
G4NAMU @ AAPM, Seattle, WA July 24-28, 2005
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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
G4NAMU @ AAPM, Seattle, WA July 24-28, 2005
17
Prostate brachytherapy - HDRProstate brachytherapy - HDR
HDR 192Ir source, MicroSelectron
Ejection spectrum
Preliminary results
keVA. Allard, Summer Project