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Geant4 in Brachytherapy

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

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Geant4 in Brachytherapy

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

  3. 3.5 mm 1.1 mm 0.6 mm 5 mm 2 m Modeling of encapsulated 192Ir source(Courtesy of McGill University) MicroSelectron Classic HDR source (part no. 080950) G4NAMU @ AAPM, Seattle, WA July 24-28, 2005

  4. 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) 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 materials We collect phase space files of photons reaching the applicator surface and use the data for dose calculations in patient geometry. 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. G4NAMU @ AAPM, Seattle, WA July 24-28, 2005

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

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

  9. Validation of the model: radial dose fonction Prostate brachytherapy - LDR LDR 125I source, Amersham 6711 J.-F. Carrier, Ph.D. project G4NAMU @ AAPM, Seattle, WA July 24-28, 2005

  10. 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 This interseed attenuation is not considered in TG43 (clinical) dose calculations 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 G4NAMU @ AAPM, Seattle, WA July 24-28, 2005

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

  12. 32 z 1 z y Hampton University(Collaboration: NIST, EVMS) Scintillating Fiber based Beta Detector → Absolute calibration of sources Lawrence Tynes, Ph.D.: Detector Nnenna Onumah, Ph.D.: Geant4 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 G4NAMU @ 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. G4NAMU @ AAPM, Seattle, WA July 24-28, 2005

  15. ALLS FacilityUltrafast 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 G4NAMU @ 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!!! G4NAMU @ AAPM, Seattle, WA July 24-28, 2005

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

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