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

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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)

rad

ial d

os

e f

un

cti

on

g(r

)

GEANT4

Williamson 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, t

het

a)

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

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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

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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 PLAN

77 seeds

0.6 mCi activity

1.7% of the D90 value is lost due to interseed attenuation

BLUE PLAN

137 seeds

0.3 mCi activity

3.3% of the D90 value is lost due to interseed attenuation

Dr. Paul Gueye Hampton University

G4NAMU @ AAPM, Seattle, WA July 24-28, 2005

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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

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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

z32

Dr. Paul Gueye Hampton University

G4NAMU @ AAPM, Seattle, WA July 24-28, 2005

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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

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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

keV

A. Allard, Summer Project