Geant4 in Brachytherapy Brachytherapy: Brief Overview Clinical applications Basic research Ultrafast & biology applications Issues for the work group Dr. Paul Gueye Hampton University G4NAMU @ AAPM, Seattle, WA July 24-28, 2005

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

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

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, 809-819, 1995) Dr. Paul Gueye Hampton University G4NAMU @ AAPM, Seattle, WA July 24-28, 2005

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

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

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

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

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

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

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] http://www.physmed.phy.ulaval.ca/phys_med/DICOM Dr. Paul Gueye Hampton University G4NAMU @ AAPM, Seattle, WA July 24-28, 2005

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

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

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

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

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

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