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A selection of Geant4 medical physics applications

This talk highlights the applications of Geant4 in medical physics, including the verification of beam system for 3D dose distribution and the calibration of brachytherapy sources. It also discusses the use of Geant4 in scatter compensation for megavoltage 3D CT and in vivo dosimetry for mammography. Various examples and ongoing activities are presented.

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A selection of Geant4 medical physics applications

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  1. A selection of Geant4 medical physics applications Maria Grazia Pia INFN Genova and CERN

  2. The Magic Cube (INFN Torino) Verification of the beam system to compare the prescribed and delivered 3D dose distribution • Sandwich of 12 parallel plate (25x25) cm2 ionization chambers • Each chamber: • passive material (N2,G10,Mylar) • anode (0.035 mm Cu) • active material (3 mm N2) • passive material • air gap (2 cm, tissue equivalent of adjustable thickness) • Thickness of a chamber as water equivalent ~1.1 mm Between the two chambers and the remaining ten ones there is room to insert a plastic absorber (thickness to choose to match the depth through the proximal edge of the SOBP)

  3. A chamber of the Magic Cube • Air 6 mm • Mylar 0.05 mm • N2 3 mm • G10 0.1 mm • Cu (cathode) 0.035 m • N2 3 mm (active) • Cu (anode) 0.035 mm • G10 0.1 mm • N2 6 mm • Mylar 0.05 mm • Air 6 mm • Air 20 mm

  4. Tests with theMagic Cube • Test at GSI (Carbon beam) • linearity: better than 1% • uniformity: better than 3% • position and width: precision of about 1 mm • Test at PSI (proton beam) • Protons beam of 137 MeV • Cube rotated by 180o • No absorbers inside the Cube • Range shifter of water in front of the Cube • Test at CPO Orsay (p beam)

  5. Bragg peak, Magic cube data and Geant4 Experimental data: Bragg peak of a 270 MeV/u carbon ion beam distance(cm) Geant4 and experimental data, PSI test with proton beam

  6. Brachytherapy(National Inst. Cancer Research, Genova) • Application of Geant4 to the verification of a brachytherapy calibration procedure • Calibration of the radionuclide source strength is an essential part of any brachytherapy QA programme • MicroSelectron High Dose Rate (HDR) system at Nat. Inst. Cancer Research • The MicroSelectron Ir-192sources are supplied by Mallinckrodt Medical B. V. - Holland with a calibration certificate specifying the Air Kerma Rate measure at a distance of 1 m with an uncertainty of  5 % • To verify the procedure to calibrate each new MicroSelectron HDR brachytherapy source Geant4 is used to obtain simulated source Air Kerma Rate at distance of 1 m and simulated isodose distribution for the calculation of anisotropy coefficients for unshielded and shielded vaginal treatments • Geant4 Low Energy electromagnetic physics processes • Geant4 Radioactive Decay Module

  7. Brachyterapy at Nat. Inst. Cancer Research, Genova S. Agostinelli, R. Corvo, F. Foppiano, S. Garelli, G. Sanguineti • The source holder is a standard endobronchial treatment catheter, the chamber is a 0.6 cc Capintec chamber connected to a Capintec 192 electrometer • The IST group follows the direction of Basic Dosimetry on Radiotherapy with Brachytherapy Source of the Italian Association of Biomedical Physics (AIFB) The custom calibration plexiglas jig, used for in air measurements.

  8. Treatment planning with Geant Geant interfaced to a file obtained with a Computer Tomography (CT) scan Reconstruction of the optical nerves (black pixels) Reconstruction of the lung contour (black pixels) CT slice of a head with the dose deposition of a proton beam obtained with the GEANT code

  9. CT interface and treatment planning Two possible approaches: • CT interface + Geant4 “full simulation” • CT interface + Geant4 “fast simulation”(physics processes parameterised through an analytical treatment) • Geant-based tools for • inverse planning • technique of active dose delivery • Software interface for Geant4 that reads input data in DICOM3 format developed at Medical Dept., University of Piemonte Orientale and INFN Torino

  10. Geant4 for scatter compensation in Megavoltage 3D CT • Use GEANT4 to obtain digitally reconstructed radiographs (DRRs), including full scatter simulation • This represents a great improvement over approaches based on ray-casting.

  11. Use of Geant4 for scatter compensation in Megavoltage 3D CT • The study of DRRs synthesized by Geant4 allows users to produce a model for scatter compensation of megavoltage radiographs • This will help to produce a more accurate megavoltage 3D CT reconstruction and therefore a more reliable tool for patient positioning and treatment verification • Activity in progress at the Italian National Institute for Cancer Research, Genova • Other possible areas of application of Geant4: • LINAC head simulation • Scatter analysis in total body irradiation

  12. In vivo dosimetry for mammography • TLD characterization for mammography screening • simulation of dose deposition and glow curve • Mammography simulation • Goal: minimize dose on patient • Comparison between experimental data TLD in vivo dosimetry and Geant4 simulation • Activity at Medical Physics Dept., Umberto I Hospital of Ordine Mauriziano, Torino • in progress

  13. Acknowledgments Many Geant4 collaborators and users have contributed to this talk: • S. Agostinelli, F. Foppiano, S. Garelli (Nat. Inst. for Cancer Research) • R. Gotta (TERA) • F. Bourhaleb, S. Chauvie, G. Nicco (INFN and Univ. Torino) • V. Rolando (University of Piemonte Orientale) • P. Nieminen (ESA)

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