Medical Applications in Europe Diagnosis : detector design for imaging External therapy Hadrontherapy Dosimetry Computing Testing and validation

Transcription

1 Medical Applications in Europe & The Geant4 DNA project on behalf of many Geant4 developers & users Sébastien Incerti Centre d Etudes Nucléaires de Bordeaux-Gradignan CNRS / IN2P3 / Bordeaux 1 University France G4NAMU meeting SLAC 6 March, 2006

2 Talk s highlights Medical Applications in Europe Diagnosis : detector design for imaging External therapy Hadrontherapy Dosimetry Computing Testing and validation The Geant4 DNA project

3 Medical Applications in Europe : Detector design for diagnosis

4 GATE : a simulation toolkit for emission tomography in nuclear medicine and molecular imaging Team : I. Buvat, INSERM / CHU Pitié S., France and the GATE collaboration Optimize detector design, assessing acquisitions Home made code available, from 1995 to 1999 After 1999, 8 home made codes and 7 publicly released. Released in May More than 400 users to the gate user mailing list Based on Geant4, written in C++, user-friendly (macros) Time dependence (source, detector) important for SPECT / PET imaging Realistic simulations of data acquisitions in time Modelling of detector response using digitization Use of decay module for source decay kinetics Voxelized or analytical phantoms Gate slow : emitting object large, voxelised maps, tracking slow through any border, low detection efficiency : high stat needed. Use accelerating methods : variance reduction technique, combine MC and non MC, parallel simulation

5 Multi modality imaging system dedicated to small animal Team : D. Brasse et al., ULP-IRES, France SPECT : Single Photon Emission Computed Tomography PET : Positron Emission Tomography CT : Computed Tomography CT SPECT PET Anatomical + functional imaging ➊ Simulation of micro-spect with G4 & comparison with references : dx < 1 mm - Scintillation Process - Definition of the scintillator material (YAP) and optical properties of the medium - Boundary Process (between YAP and Air): Al coating simulation - Surface YAP - PMT window: two dielectric materials - Comparison simu/exp in reas. agreement (Det/Emit) : pmt surf and edge effects - Simulation of matrices of 64 crystals : energy distribution, photopeak efficiency - Shielding ➋ Simulation of CT with G4 / MCNP4C / Semi-emp. model - Good agreement above 13 kev in X-ray spectrum ➌ Starting PET with GATE : geometry validated, physics

6 Simulated PET acquisition of a respiratory and cardiac moved NCAT-human torso phantom using the GATE toolkit Team : N. Lang et al., UHM, Germany Realistic experiment PET/CT scanner GATE simulated PET scan Voxelized 3D-anatomy of human body Respiratory and cardiac motion implemented Emission and attenuation configuration Simulation of lesion or infarction Image Recon (STIR) Problem: Image blurring during long scan times Attenuation correction with static CT data produces artifacts in images Source Phantom GATE Simulation Attenuation Phantom Solution: Gated listmode PET freezes motion Use of software morphing (optical flow) to produce motion free images inheriting the full statistics Weeks of CPU-Time (2,4 GHz Xeon) needed for single image Attenuation increases CPU time by factor of 10! Parallel cluster computing needed (not yet implemented in GATE)

7 Clear-PEM scanner for breast cancer imaging with Geant4 Team : A. Trindade et al., LIP, Portugal Geant4 toolkit is used for the simulation of the Clear-PEM scanner (dx < 5 mm & high sensitivity) The developed simulation framework includes : - a patient model - a detailed description of the detector geometry - a C++ high-level simulator of the signal formation and data processing in the on-detector front-end and off-detector digital electronic systems was developed The NURBS CArdiac Torso (NCAT) phantom was implemented in Geant4, as a voxelized geometry (class G4VPVParameterisation) A detailed description of the scanner geometry and material properties were implemented (~35000 solids) Several 5 min. acquisition exams were simulated with Geant4 to assess lesion visibility Computational resources: 70 d CPU (140 jobs), 236 GB, data production at CERN (LXBATCH), CASTOR storage

8 Medical Applications in Europe : External therapy

9 Medical accelerator for IMRT Team : F. Foppiano et al., INFN Genova, Italy Complex geometries Variety of physics processes Low Energy Package Interactive facilities : visualization, analysis, UI geant4 Field 5 x 5 cm Field 10 x 10 cm films exp data geant4 exp data % dose at 100 mm depth in the phantom % dose with respect to the depth in the phantom

10 Treatment head simulation Team : S. Larsson et al., Karolinska U, Sweden Bremsstrahlung validation: radial dose profile High energy electron beam, 50 MeV Target 3 mm Be Accuracy in the geometry and magnetic field modeling

11 Simulations for the virtual prototyping of a radiotherapy MRI-linear accelerator system : linear accelerator output, CT-data implementation, dose deposition in the presence of a 1.5 T magnetic field Team : A. Raaijmakers et al., UMC Utrecht, The Netherlands Simulation of a radiotherapy accelerator has been achieved CT-data implementation is working fine and is showing agreement with TPS PLATO Already, physicians come up with clinical cases of inhomogeneous target volumes in patients, where they want to know the dose distribution more accurately Need to validate the simulated dose distributions with linear accelerator in a magnetic field from MRI scanner (better dose control) Ionization chamber response in a magnetic field is still a problem GEANT4 is a very practical tool for our purposes, though there is room for some improvement (navigation, boundary crossing)

12 Medical Applications in Europe : Hadrontherapy

13 Hadrontherapy : proton beam line Team : P. Cirrone et al., INFN Catana, Italy Modeling of the Catana proton beam line Electromagnetic and hadronic interactions for protons, ions (and secondary particles) agreement with data better than 3% Modulator for hadrontherapy beam line

14 Medical Applications in Europe : Dosimetry

15 Microdosimetry at the cellular scale Team : S. Incerti et al., CENBG / IN2P3, France Cells in growing medium (water) Culture layer (Mylar) Ambie nt air 40 from 0.9e-3 to 6e-3 500e- 3 Object collimator Ø=5 µm (platinum) Beam pipe (aluminium) Alpha beam Diaphragm Ø=10 µm (platinum) Beam pipe (aluminium) Magnetic volume : 4 quadrupoles with fringing field Beam pipe (aluminium) Collimator Ø=10 µm (platinum) Exit window Gas (Si 3 N 4 ) detector (isobutan e) Ambien t air Culture foil (polypropyle ne) Cells in KGM (water) Microscope slide (glass) Alph a sourc e Gold foil Alphas 16 Beam pipe (vacuum) Extraction window (Havar) Ambientair Culture layer (Mylar) Cellsin growing medium (water) e -4 4e Alpha beam Comparaison of cellular irradiation setups : microbeam (CENBG), classical macrobeam, electrodeposited sources of radioactive emitters : hit and dose distribution within cellular population Dévelopment of realistic voxellized phantoms at the cell scale : nucleus, cytoplasm, mitochondria from 3D confocal microscopy Geant4- DNA project Ray-tracing in quadrupoles at the sub-micron scale for nanobeam line design 5e e e-3 Cell layer cells / 1.54 cm 2

16 Anthropomorphic phantoms for dosimetry Team : M.G. Pia et al., INFN Genova, Italy Development of anthropomorphic phantom models for Geant4 : evaluate dose deposited in critical organs : radiation protection, total body irradiation Original approach analytical and voxel phantoms in the same simulation environment facilitated by the OO technology Male and Female Application : Total Body Irradiation is used as a method of preparation for bone marrow transplantation for leukemias and lymphomas. Low dose TBI is sometimes used to treat disorders of the blood cells such as low grade lymphoma and does not require bone marrow transplant or stem cells. In TBI, the dose calculation is based on dosimetry using a phantom Geant4 analytical phantom ORNL model, female 1 skull 2 thyroid 3 spine 4 lungs 5 breast 6 heart 7 liver 8 stomach 9 spleen 10 kidneys 11 pancreas 12 intestine 13 uterus and ovaries 14 bladder 15 womb 16 leg bones 17 arm bones

17 Brachytherapy Team : S. Guatelli et al., INFN + IST Genova, Italy Dosimetry for all brachytherapy devices Dosimetry Endocavitary brachytherapy Dosimetry Interstitial brachytherapy MicroSelectron-HDR source Dosimetry Superficial brachytherapy Leipzig applicator Bebig Isoseed I-125 source F. Foppiano, IST and Susanna Guatelli, INFN Genova

18 Betadosimetry and Activity Measurements in Brachytherapy Team : M. Schubert et al., LMU, Germany Activity with PIPS Brachytherapy for glaucoma Conversion e-

19 GATE for brachytherapy applications Team : C. Thiam et al., LPC Clermont IN2P3, France GATE is already in use for dosimetry applications in both animal and human models Ocular brachytherapy using 106Ru/106Rh applicator with GATE Brachytherapy application using Iodine 125 sources : a study for kerma/dose calculation with «track length estimator» method is under validation Optimization of the execution speed, improved flexibility in the dose calculation module Validation studies in the use of GATE for internal and external dosimetry applications (impact of cuts, detection volume and physics models) GEANT4 validation for dosimetry related to the electrons (tests of the multiple scattering in the next versions) Dosimetry on images patient voxelized (modeling with real patients data) GATE simulations in a grid environment The computation time was reduced although not sufficiently for clinical practice: further optimisations are going on (local clusters at LPC & CC IN2P3) Submission and retrieval times are very important using sequential submission (need to use multithreaded submission) A GENIUS web portal has been created to ease the access to this applications for the medical physicists Real production is done on grid infrastructure (GATE is an application pilot for biomedical applications in EGEE Enabling Grid for E-sciencE) Inter-connection between web and grid services needs to be validated on production infrastructure

20 Medical Applications in Europe : Computing issues

21 Improve simulation s performance in terms of speed Parallelisation of the Geant4 application on a local cluster See computation time gain by S. Chauvie et al., Ordine Mauriziano + INFN Torino, Italy but a hospital may not own a sufficient computer farm Varian 600C/D Millenium 120-leaf MLC Access to distributed computing resources share with other institutes computing resources geographically distributed around the world many GRID projects An infrastructure and standard interfaces capable of providing transparent access to geographically distributed computing power and storage space in a uniform way interface application / GRID : DIANE project DIANE is a intermediate layer between applications and a local cluster or the GRID. Same application code as running on a sequential machine or on a dedicated cluster or on the GRID completely transparent to the user. prototype for an intermediate layer between applications and the GRID

22 Improve simulation s performance in terms of speed Increase sampling of interesting events Idea: increase sampling of interesting events : source biasing, leading particle biasing, geometry splitting, weight windows, forced detection Introduces bias, which is corrected for by introducing statistical weights The efficiency of these techniques is inversely related to the sensitivity of the detector The acceleration compared to an analogue simulation is between 5 and 15 for Geometrical Importance Sampling and between 105 and 159 for Forced Detection The FD code currently only covers the effects of nuclear decay and Compton scattering. An extension to include Rayleigh scattering and / or the photoelectric effect is considered. Especially lead fluorescence is not yet dealt with correctly FD is being integrated into GATE without modifications to Geant4 Importance Sampling in Gate J. De Beenhouwer et al., Gent U., Belgium Pseudo random generators Possible issues to optimize stochastic simulation time with parallel sequences R. Reuillon et al., ISIMA, France optimize the whole computing time of Geant4 simulation relying on parallel independent experiments which suppose a sound distribution of pseudorandom numbers optimize the access speed to random numbers independently from the generation algorithm

23 Medical Applications in Europe : Testing and validation

24 Fragmentation of light nuclei in water phantoms Team : I. Pshenichnov et al., FIAS, Germany Geant4 validation for heavy-ion therapy Both Bragg peak position and shape are well described by GEANT4 v7.0 with its "standard" electromagnetic model and binary cascade / Fermi breakup models. The peak position is predicted with accuracy of ~1-2 mm for carbon and oxygen ions in the energy range from 135A to 330A MeV. The calculations with the mean ionization potential for water I=70.89 ev (default value) are in reasonable agreement with proton and heavy ion data. The energy deposition beyond the Bragg peak due to projectile fragmentation can be described with an accuracy of ~10%. Secondary neutrons from proton and ion beams : harmful? No! Fast neutrons go through the phantom easily: may concern the shielding of the treatment room. Low energy (~ MeV) neutrons have a large probability to interact, but can deposit only low energy on average (~ 0.01 MeV/mm) The dose from neutrons is below 1.5% of the total dose for typical irradiation conditions. Depth-dose distributions were calculated. Physics of secondary neutrons was studied. The distributions of positron emitting fragments were calculated. GEANT4 v7.0 seems to be well suited for heavyion therapy simulations!

25 Light ion transport in a water phantom Team : I. Gudowska et al., Karolinska U, Sweden Problems with accurate comparison with experiments : beam energy in front of the phantom, beam energy spread use in MC calculations of the recommended stopping power data ICRU49 (p,α), ICRU73 (heavier ions) Position of the Bragg peak obtained by different MC codes within ± 2 mm Geant4 results agree reasonably well with the experimental data regarding position & height of the Bragg peak Contribution to the energy deposition from the fragmentation processes is quite good for ions up to 12 C and energies up to 200 MeV/u, Geant4 reproduces well the Bragg peak curve in this energy region For higher ion energies above about 200 MeV/u verification of the nuclear inelastic interactions required Validation of the partial cross-sections for production of secondary particles necessary Energy deposition normalized to the integral Carbon ions 195 MeV/u water target SHIELD-HIT ver 1 GEANT4 ver 7.1 Bin Casc, Stand EM G4 195 LowEn Oct13 norm int(0-15) EXP GSI Krämer et al Depth (cm)

26 Comparison with commercial treatment planning systems Team : M.C. Lopes al., LIP, Portugal CT-simulation with a Rando phantom Experimental data obtained with TLD LiF dosimeter CT images used to define the geometry - a thorax slice from a Rando anthropomorphic phantom Agreement better than 2% between GEANT4 and TLD dosimeters Profile curves at 9.8 cm depth PLATO overestimate the dose at ~ 5% level

27 Slides, videos and contact details available at 10 th Geant4 user and workshop conference Bordeaux, France 3-10 November

28 The Geant4 DNA project on behalf of the Geant4 DNA collaboration Sébastien Incerti Centre d Etudes Nucléaires de Bordeaux-Gradignan CNRS / IN2P3 / Bordeaux 1 University France The concept of dose fails at cellular and DNA scales ; it is desirable to gain an understanding of the processes at all levels (macroscopic vs. microscopic)

29 Geant4 DNA Simulation of Interactions of Radiation with Biological Systems at the Cellular and DNA Level Based on Partly funded by European «open» collaboration between R. Capra, S. Chauvie, R. Cherubini, Z. Francis, S. Gerardi, S. Guatelli, G. Guerrieri, S. Incerti, B. Mascialino, G. Montarou, Ph. Moretto, P. Nieminen, M.G. Pia, M. Piergentili + biologists (E. Abbondandolo, G. Frosina, E. Giulotto et al.)

30 Geant4-DNA : scope Provide simulation capabilities to study the biological effects of radiation at multiple levels Macroscopic already feasible with Geant4 calculation of organ dose in progress : develop. useful associated tools (ex. human analytical & voxel. phantoms) Cellular level in progress : processes for cell survival expected : cell geometries modellingtalk) Experimental validation Complexity of software, physics and biology addressed with an iterative and incremental software process DNA level in progress : physics processes at the ev scale (direct effects) expected : DNA modelling expected : chemical processes for radical species production (indirect) expected : DNA strand breaking, fragmentation (up to 10-6 s after irradiation) Parallel development at all three levels (domain decomposition) First phase in : Collection of user requirements & first prototypes Second phase in : Software development & release Applications involve radiobiology, radiotherapy, space radioprotection, grid Experimental validation

31 Anthropomorphic phantoms Macroscopic level Development of anthropomorphic phantom models for Geant4 evaluate dose deposited in critical organs radiation protection studies in the space environment other applications, not only in space science Original approach facilitated by the OO technology analytical and voxel phantoms in the same simulation environment mix & match Status: first release December 2005 G. Guerrieri, Thesis, Univ. Genova, Oct Relevant to other fields, not only space radiation protection Total Body Irradiation (radiotherapy)

32 TARGET THEORY models for cell survival Cellular level MODEL REFERENCE SURVIVAL FUNCTION VARIABLES Single-hit S = exp(-d / D 0 ) - Dose Multi-target single-hit Multi-target single-hit Revised model Lea (1955) S = 1- (1 - exp(-qd) ) n S = exp(-q 1 D) [ 1- (1- exp(-q n D)) n ] - Dose - Probability to hit a target - Total number of targets - Number of targets hit Single-target multi-hit Single-target two-hits S= exp(-ßd 2 ) Joiner & Johns S= exp(-α R [1 + ( α S / α R -1) e -D/Dc ] D ß D ) Cell survival equations based on model dependent assumptions No assumption on Time Enzymatic repair of DNA In progress : calculation of model parameters from clinical data E. L. Alpen «Radiation Biophysics», Academic Press, 2nd edition, San Diego, California USA, 1998

33 MOLECULAR THEORY models for cell survival More sophisticated models Radiation action Linear-quadratic model Chadwick and Leenhouts (1981) S = exp(-p ( α D + ß D ) ) - Dose - Number of times a target is hit - Conditional probability function Dual radiation action Kellerer and Rossi (1971) S = S 0 exp(- k (ξ D + D ) ) - Dose - Biological effectiveness factor - Fraction of dose related to SSBs and to DSBs - Unrestored fraction of bonds - Effectiveness factor Repair-misrepair Linear repair quadratic misrepair Repair-misrepair Linear repair - misrepair Tobias et al. (1980) S = exp -αd [1+(αDT/ε)] ε S = exp -αd [1+(αD/ε)] εφ - Dose - Max time for repair - Linear repair constant - Quadratic repair constant - Probability for linear repair - Probability for quadratic repair Lethal-potentially lethal S=exp[-N TOT [1+ N PL /[ε (1-e- εbatr )] ]ε ] Lethal-potentially lethal Low dose approximation Lethal-potentially lethal High dose approximation Lethal-potentially lethal Linear-quadratic approximation Curtis (1986) S = exp(-η AC D) - ln[ S(t)] = (η AC + η AB ) D-ε ln[1 +(η AB D/ε)(1-exp(-ε BA tr))] - ln[ S(t)] = (η AC + η AB exp(-ε BA tr) ) D + (η 2 AB /2ε)(1-exp(- ε BA tr) 2 D 2 ] - Dose - Max time for repair - Number of lethal lesions - Number of potentially lethal lesions - Constants related to lesion processes - Constants related to repair processes E. L. Alpen «Radiation Biophysics», Academic Press, 2nd edition, San Diego, California USA, 1998

34 Status of Physics processes Development of track structure modelling based low energy processes in liquid water Our goal is the development of step-by-step electromagnetic interactions for Electrons between 7 ev and 10 kev Protons, alphas and charge states between 1 kev and 10 MeV DNA level The processes considered are Elastic scattering (relevant only for electrons) Excitation of liquid water molecules Ionisation of liquid water molecules Charge exchange processes involving water molecules The software framework is based on a major design using policy based class design. Implementation and unit testing at advanced stage. Beta release for summer Long term plan is to have a reliable and maintainable framework not only for water processes, but also for other materials-dependent processes (component irradiation) Elastic Excitation Charge decrease Charge increase Ionization Electrons Protons (H+) Hydrogen (H) Alpha (He++) He+ He Brenner ( ev) Emfietzoglou (> 200 ev) Submitted to Radiation Protection and Dosimetry (2006) Negligible effect Negligible effect Negligible effect Negligible effect Negligible effect Emfietzoglou Miller and Green Miller and Green Miller and Green Miller and Green Negligible effect Born (7 ev 10 kev) Born (100 ev 10 MeV) (1 kev 15 MeV) (1 kev 15 MeV) (1 kev 15 MeV) Not pertinent to this particle Not pertinent to this particle In progress Dingfelder (100 ev 2 MeV) Not pertinent to this particle Rudd ( kev) In progress (> 500 kev) Not pertinent to this particle Miller and Green Dingfelder (0.1 Kev 100 MeV) Dingfelder Dingfelder (100 ev 2 MeV) (100 ev 2 MeV) Not pertinent to this particle Not pertinent to this particle Dingfelder Dingfelder (100 ev 2 MeV) (100 ev 2 MeV) Rudd ( MeV) In progress In progress In progress

35 Development process Complex domain physics software Collaboration with theorists Innovative design introduced in Geant4 Policy-based class design Parameterized classes: policies are cross section models, models for final state calculation etc. Flexibility of modeling + performance optimization Collaboration with experimentalists for model validation Geant4 physics validation at low energies is difficult!

36 Problems domain decomposition Testable process Water processes algorithms (policy based) Total cross section policies Angular distribution policies Electrons & charged Ions Manager Analytical models Tables-based models Different algorithms will be able to use same policies The same algorithm will be able to use different policies Files tables generation 1-dimensional interpolated datasets (cross sections) Data files 2-dimensional interpolated datasets (energy distributions for ionization)

37 Electron elastic scattering Total cross section D. J. Brenner and M. Zaider, Phys. Med. Biol. 29 N.4 (1983) D. Emfietzoglou et al., J. Phys. D: Appl. Phys. 33 (2000) B. Grosswendt and E. Waibel, Nucl. Instr. Meth. 155 (1978) D. Emfietzoglou et al., Phys. Med. Biol. 45 (2000) Phys. Med. Biol. 45 (2000) Brenner Emfietzoglou Solid line is our model Angular distribution J. Phys. D 33 (2000) Preliminary 10 ev 100 ev 200 ev 500 ev Geant4 Collaboration Workshop 3-10 November 2005 R. Capra 1 kev 37

38 Excitation (e - or p) + H 2 0 (e- or p) + H 2 0 * Total cross section p + H 2 0 p + H 2 0 * Preliminary e - + H 2 0 e - + H 2 0 * M. Dingfelder et al., Rad. Phys. Chem.. 59 (2000) D. Emfietzoglou et al., Phys. Med. Biol. 48 (2003) D. Emfietzoglou et al., Nucl. Instrum. Meth. B 193 (2002) J. H. Miller and A. E. S. Green, Rad. Res 54 (1973) Geant4 Collaboration Workshop 3-10 November 2005 R. Capra 38

39 Excitation Total cross section He + H 2 O He + H 2 O * He + + H 2 O He + + H 2 O * He ++ + H 2 O He ++ + H 2 O * σ(m 2 ) Preliminary E(eV) Geant4 Collaboration Workshop J. H. Miller and A. E. S. Green, Rad. Res 54 (1973) M. Dingfelder et al., proceedings of the Monte 3-10 November Carlo conference, R. Capra to be published 39

40 Ionisation (p or H) + H 2 0 (p or H) + e - + H σ(m 2 ) H + H 2 0 H + e - + H p + H 2 0 p + e - + H M. Dingfelder et al., Rad. Phys. Chem.. 59 (2000) E. Rudd, Nucl. Tracks Radiat. Meas. Vol 16, No. 2/3 (1989) Proton (< 500 kev) and Hydrogen ionisation implemented Development of remaining ionisation processes still ongoing Geant4 Collaboration Workshop 3-10 November 2005 R. Capra Preliminary ln(e/ev) 40

41 Charge transfer Protons, alphas and charge states M. Dingfelder et al. Rad. Phys. Chem. 59 (2000) J. H. Miller and A. E. S. Green Rad. Res 54 (1973) M. Dingfelder et al., proceedings of the Monte Carlo 2005 conference p + H 2 0 H + H H + H 2 0 p + e - + H 2 0 Preliminary Helium Charge transfer by protons/hydrogen/helium is implemented Geant4 Collaboration Workshop 3-10 November 2005 R. Capra 41

42 Biological models in Geant4 Relevance for space : astronaut and aircrew radiation hazards

43 Aurora European Programme for the Exploration of the Solar System The objective of the Aurora Programme is first to formulate and then to implement a European longterm plan for the robotic and human exploration of solar system bodies holding promise for traces of life. Shielding Human phantom

44 Scenario for AURORA Geant4 simulation space environment + spacecraft, shielding etc. + anthropomorphic phantom Dose in organs at risk Geant4 simulation with biological processes at cellular level (cell survival, cell damage ) Oncological risk to astronauts Risk of nervous system damage INFN Genova Phase space input to nano-simulation Geant4 simulation with physics at ev scale + DNA processes

45 Summary Geant4 offers powerful geometry and physics modelling in an advanced computing environment Geant4 is being extended to a novel field of simulation capability and applications biological effects of radiation at the cellular and DNA level extension facilitated by Geant4 architecture and sound OO technology openness to extension, without affecting Geant4 kernel wide spectrum of complementary and alternative physics models Three levels Macroscopic / dose cell DNA On-going activity at all levels anthropomorphic phantoms, cell survival models, low energy physics extensions down to the ev scale etc. Key elements Rigorous software process Collaboration with domain experts (biologists, physicians) Team including groups with cellular irradiation facilities

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47 Thank you for your attention