Results on Proton Tomography - PowerPoint Presentation

1. Results on Proton Tomography Prima – RDH – IRPT CollaborationC. Civinini1, M. Bruzzi1,2, N. Randazzo3, M. Rovituso4, M. Scaringella1, V. Sipala5,6, F. Tommasino41INFN - Florence, Florence, Italy2Physics and Astronomy Department, University of Florence, Florence, Italy3INFN - Catania, Catania, Italy4INFN - TIFPA, Trento, Italy5INFN - Laboratori Nazionali del Sud, Catania, Italy6Chemistry and Pharmacy Department, University of Sassari, Sassari, Italy7Physics Department, University of Trento, Trento, Italy13° Trento workshop on Advanced Silicon Radiation DetectorMax-Planck-Institut für Physik, München19-21 February 2018

2. Why proton Computed Tomography?Carlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenHadron therapy exploits the sharp shape of the Bragg peak to precisely irradiate a tumor. But to define a threatment plan To potentially reduce inaccuracies in hadron teraphy we need: 1) Direct measurement of the 3D proton stopping power (SP) maps;2) Patient positioning and treatment in one go.Treatment planning presently uses proton stopping power maps extracted from x-ray CTs resulting in errors on Bragg peak position up to a few millimeters. B. Schaffner and E. Pedroni Phys. Med. Biol. 43 (1998) 1579–1592February 21st 20182

3. How to perform a proton TomographyCarlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenTo mitigate the effect of the multiple Coulomb scattering we need an event-by-event measurement:1) Tracker to measure the proton Most Likely Path (MLP)  Silicon microstrip detectors (~70 mm point resolution);2) Calorimeter to assign an energy loss to each proton track  YAG:Ce scintillating calorimeter (~2% energy resolution @ 200 MeV);3) Image reconstruction  Most Likely Path + Algebraic algorithms running on GPUs.February 21st 20183

4. Tracking with multiple scatteringLMeasurements: entry position and angleProton true trajectoryL  straight line with confidence limitsMeasurements: entry and exit positions and anglesL’L’  straight line withconfidence limitsMeasurements: entry andExit position and angle +Most Likely Path (MLP)calculationL’’L’’ curved trajectory withNorrower confidence limitsCarlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenFebruary 21st 20184

5. Most Likely Path in a pCT geometryCarlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenMLP example with 200MeVkinetic energy protons in20cm of water:Entry: Y(0) = 0.2cm Y’(0) = -10mradExit: Y(20) = -0.1cm Y’(20) = +10mradSilicon microstrip detectors: 320mm thick 200mm strip pitchMLP error envelope plus contributions from detector position measurement error (~ pitch/√12) and MCS inside the silicon sensors The sensor thickness contribution affects only the MLP error at the edge of the phantoms ~ 150-250mm 200MeV in90MeV outStarting from D.C. Williams Phys. Med. Biol. 49 (2004) and R.W. Shulte at al. Med. Phys. 35 (11) (2008) 5 cm of air have been inserted in front and behind the 20cm H2O phantom February 21st 20185

6. Algebraic Reconstruction TechniquesThe tomographic reconstruction problem is to solve, for Sj (stopping power value in pixel j), the following set of equations:N = number of pixels; M number of protonsIn our case: N = (512x512x64)=16777216 voxelsM = 54.3*106 events (in 40 angles)Carlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenWhere: ...  February 21st 20186

7. Algebraic Reconstruction TechniquesThe system could be solved using an iterative formula:Carlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenSk image vector at iteration k (stopping power)wi ith track length in each pixel (vector)  Tracker + MLPpi stopping power integral (number)  Calorimeterlk relaxing factor (constant value or 0 as ~k-1)S0 initial image: {0} or approx (i.e., from FBP reconstruction).ART implementations:Ak = {single event}: ART  too much ‘salt-pepper’ noiseAk = {full data set}: SART (simultaneous ART)  better noise + parallel implementationAk = {1/n of the full data set}: BI-SART (n-Block iterative SART)  good noise performance + faster convergence + parallel implementation1) S. Kaczmarz Bulletin International de l'Académie Polonaise des Sciences et des Lettres. Classe des Sciences Mathématiques et Naturelles. Série A, Sciences Mathématiques, 35, pp. 355–3572) Gordon, R; Bender, R; Herman, GT J. Theor. Biol. (1970) 29 (3): 471–81.Sk+1= Sk + lk(pi - <wi,Sk>) wi} / ǁwiǁ2 February 21st 20187

8. INFN-Prima pCT apparatusCarlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenBeam test July 2017 at Trento proton Therapy Center experimental beam lineProton energy: nominal 228 MeV (214 MeV at phantom)February 21st 201885x20 cm2 field-of-view

9. Tracker4 Tracker planes4x2 silicon microstrip p-on-n sensors (HPK + FBK production), 200mm pitch, 320mm thick6x8 front-end chips (discriminators - 32 channels each), single channel I2C programmable thresholds designed in collaboration with INFN-Cagliari2 levels FPGA (data reduction + event building + serial transmission)8 data + clk serial lines (1.6Gbs)Central DAQ board ML605 Xilinx Virtex 6 development board (1GB DDR3 memory + 1Gbs Ethernet interface + I2C + RS232)  3° level FPGAFMC Interface board (serial receivers + handshake + I2C+ spares)Carlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenFebruary 21st 20189

10. Tracker planeCarlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenX-side viewFebruary 21st 201810

11. Front-endchipINFN-CaTracker architectureCarlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenSilicon sensorFront-endchips1° level FPGA2° level FPGA1° level FPGA3° level FPGAInterface boardFebruary 21st 201811

12. Calorimeter2x7 YAG:Ce crystals 3x3x10 cm370 ns scintillating light decay timeHamamatsu 18x18 mm2 photodiodes (S3204)Analogue amplifier + shaper (1ms)NI-5751 ADC (14 bits - 5 MHz sampling)Main trigger generator + sync infoIndependent crystal trigger logicNeighborhood merging (4-6 elements)7 bit event number to tracker for synchronismCarlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenFebruary 21st 201812

13. 2x7 YAG:Ce Crystals Array 3x3x10cm3CalorimeterCarlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenCalorimeter front facePhotodiodesCalorimeter front-end boardFebruary 21st 201813

14. PhantomsTwo CIRS phantomsElectron density calibration phantom18 cm diameter, 5 cm height: Water equivalent container + 9 plugsAnthropomorphic phantomHuman head with titanium spine prosthesis and tungsten dental fillingMotorized platformInserted between plane 2 and 3Phi and Z movements (Physik Instrumente, linear and step motors)RS232 remotely controlledCarlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenFebruary 21st 201814

15. Electron density phantomCarlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-München8 lateral plugs:Liver 1.07 gcm-3Lung exhale 0.50 gcm-3Breast 0.99 gcm-3Bone 1.53 gcm-3Muscle 1.06 gcm-3Bone 1.16 gcm-3Adipose 0.96 gcm-3Lung inhale 0.20 gcm-3Central plug:6 mm diameter Titanium core 4.51 gcm-3February 21st 20181512345678

16. Anthropomorphic phantomCarlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenAdult male modelDental filling in a molar (Tungsten)Spine prosthesis attached at C3-C5 vertebra (Titanum)X-Rays radiographiesTomography regionFebruary 21st 201816

17. ResultsTwo sets of data for tomography reconstructionElectron density phantom1.2x108 events in 40 anglesAnthropomorphic phantom2x108 events in 40 anglesTwo energy scan for calorimeter calibration6 energies 5x106 events each (228, 202, 169, 143, 112, 83) MeVTwo high statistics alignment run107 events each at 228 MeVCarlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenFebruary 21st 201817

18. Electron density phantom tomographyCarlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenFebruary 21st 201818Radial artifacts influence the quality of the imageThis is a known behaviour of the algebraic reconstruction algorithms  working on that issueNonetheless the plugs are (almost) visible and a quantitative analysis has been done  next slidex pixel (x400mm)y pixel (x400mm)MeV/cm

19. Relative Stopping Power (RSP)@180 MeVCarlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenFebruary 21st 201819The Titanium RSP measured value is underestimated by 13%: it has been removed from the plot (core too small, value influenced by track resolution)LungRelative Stopping Power (RSP) = Stopping Power/measured Water Stopping PowerErrors: RSP meas. = 1.3% (from water measurements), RSP expected = 1%RSP estimation from:E. Schnell, S. Ahmad, and T. de la Fuente HermanAIP Conference Proceedings 1747, 110004 (2016)Hard BoneAdipose, Water, Breast, Muscle, Liver Trabecular bone

20. Anthropomorphic phantom tomographyFebruary 21st 2018Carlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-München2064 axial slicesvoxels: 600x600x812mm3  0.3 mm3Algebraic reconstruction 25° iteration40 angles (9 deg. uniform spacing)About 5.4 x 107 events usedFirst and last slices have low statistics (outside field of view)Movie starts from lower jaw ends at upper teeth (5.2 cm range)Much lower contrast with respect to the X-Ray images mainly because of the physics of the interactions: important Z dependence for X-Ray, density dependence for protons  BUT it is what is needed for hadron therapy

21. Anthropomorphic phantom tomographyFebruary 21st 2018Carlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-München21

22. Anthropomorphic phantom tomographyFebruary 21st 2018Carlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-München22X pixels [0.6mm]X pixels [0.6mm]y pixels [0.6mm]y pixels [0.6mm]Z pixels [0.812mm]Stopping power [MeV/cm]Front (coronal) viewFront (coronal) viewLateral (sagittal) viewLateral (sagittal) view

23. ConclusionsA silicon tracker / scintillator calorimeter, 5x20 cm2 field of view, Computed Tomography apparatus has been tested in a 228 MeV proton beam for pre-clinical studies;Tissue equivalent non-homogeneous phantoms have been used for tomographic data taking;Measured RSP values agree with the expected ones;Algebraic iterative reconstruction algorithms have been implemented to run on GPU;Three dimensional images with 16.8M voxels with size of 600x600x812mm (0.3 mm3) have been reconstructed;More tests during 2018 are foreseen.Carlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenFebruary 21st 201823

24. Backup slidesCarlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenFebruary 21st 201824

25. Proton Radiotherapy → first proposed by R.R. Wilson in 1946 "Radiological Use of Fast Protons", Radiology, 47:487-491 (1946)Advantage : Highly conformational dose distribution:i) lower dose to healthy tissues in front of tumor;ii) healthy tissues beyond it are not damaged;Inaccuracies: Treatment planning presently performed by X-CT → expected errors typically of a few millimeters B. Schaffner and E. Pedroni Phys. Med. Biol. 43 (1998) 1579–1592Direct measure of the 3D stopping power maps using protonsPrecision improvement when positioning and treatment are made in one goproton Computed Tomography: principlepCTCarlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenFebruary 21st 201825

26. Algebraic Reconstruction TechniquesIterative algorithm to reconstruct tomographic images (proton stopping power maps) from a set of single proton eventsStarting point (S(x,y,E) stopping power):Introducing the mass stopping power S/r :E0 being a reference energy at which the SP is calculatedDividing by S/r at energy E: Carlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenFebruary 21st 201826

27. Algebraic Reconstruction TechniquesThe left hand side doesn’t depend too much on the material composition (≤6*10-3) and could be replaced by the one measured for liquid water (NIST pstar tables - http://physics.nist.gov/PhysRefData/Star/Text/PSTAR.html): Where Carlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenFebruary 21st 201827

28. Algebraic Reconstruction TechniquesIntegrating along the proton path:D. Wang, Med.Phys. 37 (8) (2010) 4138-4145. Ein is given by the accelerator, Eout by the calorimeter and the ‘path’ by the tracker (Most Likely Path)Subdividing the object into a set of pixels, for the ith proton:Where wij is the path length of proton i inside the pixel j Carlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenFebruary 21st 201828

29. Carlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenPixel 1wijPixel jPixel NComputational challenge: find the simplest (fastest) way to build the wij matrix (1015 elements, only 3x1010 ≠ 0 )p in200 MeVp out 90 MeVPhantom: 20 cm of waterFebruary 21st 201829

30. Motorized platformCarlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenTo be integrated in the DAQ to automatize data takingSeen from belowOff-center axis (5 cm) to allow tomographies of large objectsFebruary 21st 201830

31. Relative Stopping Power (RSP)@180 MeVCarlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenFebruary 21st 201831Relative Stopping Power (RSP) = Stopping Power / measured Water Stopping PowerRSP estimation from:E. Schnell, S. Ahmad, and T. de la Fuente HermanAIP Conference Proceedings 1747, 110004 (2016)TissueMeasured SP(MeV/cm)RSP measured (H2O meas)RSP expected(Schnell et al.)RSP difference (%)Water14,6280,99110,85Water24,7441,0161-1,64Water34,6821,0031-0,31Water44,6160,98911,10Water mean4,6671,00010,00Lung inhale0,8890,1900,1920,85Lung exhale2,5020,5360,496-8,08Adipose4,5600,9770,965-1,25Breast4,7411,0160,99-2,60Muscle4,9521,0611,056-0,47Liver5,0091,0731,065-0,76Bone 200 HA5,2401,1231,111-1,04Bone 800 HA6,6361,4221,415-0,48Titanium13,1602,8203,24313,06 Possible overestimation (bias) on RSP from artefacts

32. Large area system: radiographyCarlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenAt ‘Centro Protonterapia’ Trento, Italy - October 2016Intermediate step to full TomographyTwo tracker planes and Calorimeter CIRS Antropomorfic phantomTwo tracker planes to extrapolate the exiting proton trajectory to the calorimeter for better energy resolution and back to the head mean transverse plane for image reconstruction.Beam energy to the phantom : 180 MeV. About 107 protons per slice  90 mGyCalorimeterTracker planesFebruary 21st 201832

33. Large area system: radiographyCarlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenStopping power integral map normalizedto 180 MeV(same quantity used forTomographic Reconstruction):Pixel size 1.5mmBeam energy 180 MeVNo MLPMany thanks to TIFPA, IBA and ‘Centro Protonterapia’, TrentoFebruary 21st 201833

34. Large area system: radiographyCarlo Civinini. INFN Firenze 'Trento Workshop' @ MPI-MünchenResidual energy map:Pixel size 1.5mmBeam energy 181 MeVDose 90 mGyFebruary 21st 201834