Characterization of an X-ray source based on laser-target interaction - PowerPoint PPT Presentation

International Conference on Monte Carlo Techniques for Medical Applications (MCMA2017) 15 th - 18 th October 2017 Napoli, Italy Characterization of an X-ray source based on laser-target interaction using the Geant4 Monte Carlo toolkit. Pietro Pisciotta , Giorgio Russo, Luciano Pandola, Leonida A. Gizzi, Luca Labate, Debora Lamia, Daniele Panetta and Paolo Russo 1

Collaboration CNR-INO: Ultra-intense lasers, laser-driven UNINA: CBCT technology development, phase particle accelerators, nonlinear optics contrast X-ray imaging CNR-IFC: Preclinical multimodal molecular imaging, animal facility, CBCT technology development INFN-LNS/CNR-IBFM: Monte Carlo simulation PRIN 2015: Clinically Compatible Tool For Advanced Translational Research with Ultrashort and Ultraintense X-ray Pulses 2

Background and motivations 3

Expected results - imaging Typical small rodent heart rates Chérin et al, Ultrasound in Med. & Biol. 2006;32(5):683-91 Mice: 300-600 bpm, RR 100-200 ms Retrospective B-mode micro-US of mouse heart – single slice in-plane resolution: N.A. Rats: 170-400 bpm, RR 150-350 ms Temporal resolution in cardiac Lin et al, IEEE Ultr. Symp. (IUS) 2011; pp. 1858-61 cine mode B-mode STE – x20 0.5 mm slices • Mice and rats are the most (fps) in-plane pixel size ~50 mm validated animal models for CVD 40-50 time bin per cardiac cycle (mouse) such as heart failure and x myocardial infarction* 1000 • Real volumetric (isotropic) data 700 Micro-US ? is required to capture the this project complex 3D motion and strain of Expected range of temporal resolution in cardiac cine mode the rodent heart** x @ 80-200 mm isotropic voxel size 500 Espe et al, JCMR 2013;15:82 PC-CMR - x32 1.5 mm slices Badea et al, PMB 2011;56:3351-69 x in-plane pixel size ~100 mm 300 Cardiac cine mCT w/ fast prospective gating >20 time bins per cardiac cycle (rat) 88 mm isotropic voxel size 10 time bins per cardiac cycle High-field Micro-MRI Befera et al, Mol Im Biol 2013;Sep 14 x x 100 Cardiac 4D micro-CT with • Cardiac cine 99m Tc-tetrofosmin mSPECT 350 mm spatial resolution retrospective gating: (125 mm isotropic voxel size) 50 Pro’s: high spatial resolution, – 10 time bins per cardiac cycle isotropic . { Con’s : trade-off between – Spatial 1D 2D 2.5D temporal resolution, image 3D dimensions quality and dose. (*) Russel et al, Cardiovasc Pathol 2006; 15:318 (**) Espe et al, J Cardiovas Mag Res 2013, 15:82 4

Preclinical imaging experimental setup LASER sample Tungsten target Magnetic Bremsstranhlung e- beam dipole x-ray The X-ray source is designed on top of the laser- driven electron accelerator already running at the Intense Laser Irradiation Laboratory of the INO-CNR in Pisa. It is based upon a: 10 TW laser system delivering <40 fs duration pulses with >400 mJ energy at a 10 Hz repetition rate. This accelerator has been already proved to be able to deliver electron bunches with up to around 80 MeV with energy spread down to around 25% and bunch charge ranging from few tens of pC up to few nC. 5

MC study: geometry Aims: To design, the main characteristics of an X-ray bremsstrahlung source based on a laser- To study and driven electron beam accelerated via Laser Wake-Field Acceleration To optimize LASER sample Tungsten Development of a new Geant4 target application Magnetic Bremsstranhlung e- beam dipole x-ray geant4.10.03 version 6

Source features Spectrum of the source shape: decreasing exponential particle: e- Energy MAX = 30 MeV Source dimension = 0.5 mm Divergence = 6 ° Electron interactions are simulated, starting form an exponentially decreasing e- energy spectrum; a thin tungsten foil has been used in order to generate X-rays via bremsstrahlung. 7

What we studied… LASER Layer for spectra study sample Tungsten target 0 – 10 – 15 – 20 mm Water phantom for Magnetic Bremsstranhlung e- beam dipole x-ray dosimetric study Magnetic deflector dipole to reduce electron contamination conversion efficiency using different foil thicknesses and materials The Monte Carlo application allows studying particle spectra in the output beam many features of the resulting X-ray beam such X-ray source size as: the out-of-beam scattered radiation for external shielding design. 8

Spectra - study results %Electronic particle # contamination Results 49108 photons 11,70 Layer 1 6505 W thickness = 0.75 mm electrons 42943 photons Layer 2 11,06 electrons 5339 40559 photons Layer 3 10,55 4786 electrons 38390 photons 9,97 Gamma spectra Layer 4 4252 electrons Electron spectra MeV MeV MeV MeV MeV MeV MeV MeV 9

Spectra - study results %Electronic particle # contamination Results photons 174008 1,59 Layer 1 2815 W thickness = 4.00 mm electrons 156256 photons 1,33 Layer 2 2105 electrons 147924 photons 1,20 Layer 3 1802 electrons 140308 photons Gamma spectra Layer 4 1,07 1517 electrons Electron spectra MeV MeV MeV MeV MeV MeV MeV MeV 10

Spectra - study results %Electronic particle # contamination Results 130001 photons 1,65 Layer 1 2184 W thickness = 6.00 mm electrons 116684 photons Layer 2 1,38 electrons 1627 110394 photons Layer 3 1,23 1378 electrons 104570 photons 1,13 Gamma spectra Layer 4 1192 electrons Electron spectra MeV MeV MeV MeV MeV MeV MeV MeV 11

Photons & e- W thickness conversion efficiency using different foil particle contamination of the output beam thicknesses # bremsstrahlung photons # electrons 200000 9000 4; 174007 Best configuration 180000 8000 0.5; 7717 3; 164276 160000 7000 0.75; 6505 140000 6000 6; 130001 120000 5000 electrons photons 1.5; 4855 100000 1.5; 94046 4000 80000 10; 76132 3; 3083 3000 60000 0.75; 49108 6; 2184 2000 40000 4; 2581 0.5; 34609 10; 1362 1000 20000 0 0 0 2 4 6 8 10 12 0 2 4 6 8 10 12 Tungsten thickness [mm] Tungsten thickness [mm] 12

Dose distributions study results Results Preliminary dose distribution The x-y profile dimensions permit to cover the entire thorax dimension and, in particular, the mouse heart dimension. x10 -5 x10 -5 x10 -5 3.5 3.5 2.5 3.0 3.0 2.0 2.5 2.5 1.5 2.0 2.0 Dose [a.u.] Dose [a.u.] Dose [a.u.] 1.5 1.5 1.0 1.0 1.0 0.5 0.5 0.5 0.0 0.0 0.0 0 5 10 15 20 25 30 0 5 10 15 20 25 30 0 5 10 15 20 25 30 35 [mm] [mm] Depth [mm] − 𝑡ℎ𝑝𝑢 ≈ 10 −4 𝐻𝑧/𝑡ℎ𝑝𝑢 𝑓 ≈ 10 −12 𝐻𝑧/𝑓 − 𝐸𝑝𝑡𝑓 𝑛𝑓𝑏𝑜 𝐸𝑝𝑡𝑓 𝑛𝑓𝑏𝑜 Mouse heart dimension Thorax dimension 13

Conclusions and future impact MC allows us to simulate: Electron interactions with tungsten foil to generate X-rays via bremsstrahlung. In particular, starting form an exponentially decreasing e- energy spectrum. W thickness 4 mm yield ≈ 1% e- reaching target < 1.6% e − ≈ 10−12Gy/e− Dosemean shot ≈ 10−4Gy/shot Dosemean This preliminary work will be important to study and develop a new source to perform preclinical imaging . The next step will be to perform the system and dosimetric validation using Gafchromic film. This study lays the foundation for future laser Thompson source for imaging. 14

That’s all !!! Thank you for attention! pietro.pisciotta@lns.infn.it 15