Development of a Head Scanner for Proton CT Hartmut F.-W. - PowerPoint PPT Presentation

Development of a Head Scanner for Proton CT Hartmut F.-W. Sadrozinski R. P. Johnson, S. Macafee, A. Plumb, H. F.-W. Sadrozinski, D. Steinberg, A. Zatserklanyi SCIPP, UC Santa Cruz, CA 95064 USA V. Bashkirov, F. Hurley, R. Schulte Loma Linda University Medical Center, CA 92354 USA K. Schubert, M. Witt CSU San Bernardino, San Bernardino, CA 92407, USA S. Penfold CMR, Univ. of Wollongong NSW 2522, Australia Hartmut F.-W. Sadrozinski: pCT HSTD8 Dec. 2011 1

Large-scale Imaging with Silicon Sensors Energy Loss of Protons, r Attenuation of Photons, Z N(x) = N o e -  x dE  dE     r  E dx l dx dx X-Ray Absorption Coefficient Stopping Power for Protons 4 100 10 Bone Bone Bethe-Bloch Muscle Muscle dE/dl H2O H2O Fat 100 Fat [MeV/cm]  10 dE dE [1/cm]  r 1 dl dx keV 300mu 6 cm 1 1.000 1.000 10 0.165 1.000 100 0.006 0.699 1000 0.002 0.381 0.01 1 10 100 1000 1 10 100 1000 X-Ray Energy [keV] Proton Energy E [MeV] NIST Data Measure energy loss on individual protons Measure statistical process of X-ray removal Hartmut F.-W. Sadrozinski: pCT HSTD8 Dec. 2011 2

Proton CT Basics Proton therapy and treatment planning requires the knowledge of the stopping power in the patient, so that the Bragg peak can be located within the tumor. X-ray CT has been shown to give insufficiently accurate stopping power (S.P.) maps in complicated phantoms or from uncertainty in converting Hounsfield values to S.P. Range Uncertainties (measured with PTR) > 5 mm RSP > 10 mm > 15 mm Schneider U. (1994), “Proton H radiography as a tool for quality control Alderson Head Phantom in proton therapy,” Med Phys. 22, 353. The goal of Proton CT is to reconstruct a 3D map of the stopping power within the patient with as fine a voxel size as practical at a minimum dose, using protons (instead of x-rays) in transmission. In a rotational scan the integrated stopping power is determined for every view by a measurement of the energy loss. Hartmut F.-W. Sadrozinski: pCT HSTD8 Dec. 2011 3

pCT Challenge #1: Multiple Coulomb Scattering The proton path inside the patient/phantom is not straight  the path of every proton before and after the phantom has to be measured and its path inside the patient reconstructed. From deflection and displacement, calculate the “Most Likely Path MLP” Beam test with sub-divided phantom: MLP can be predicted with sub-mm precision using tracking detectors with ~ 80  m resolution 0 0 .5 .5 RMS = 490um RMS = 490um 0 0 .4 .4 MLP width = 380 um MLP width = 380 um 0 0 .3 .3 0 0 .2 .2 0 0 .1 .1 ] ] ent [cm ent [cm 0 0 isplacem isplacem -0 -0 .1 .1 -0 -0 .2 .2 D D -0 -0 .3 .3 -0 -0 .4 .4 -0 -0 .5 .5 D C Williams Phys. Med. Biol. 49 (2004) 2899 – 2911 0 0 2 2 4 4 6 6 8 1 8 1 0 1 0 1 2 1 2 1 4 1 4 1 6 1 6 1 8 2 8 2 0 0 D D e e p p th th in in s s id id e e A A b b s s o o rb rb e e r [c r [c m m ] ] Hartmut F.-W. Sadrozinski: pCT HSTD8 Dec. 2011 4 M. Bruzzi et al IEEE Trans. Nucl. Sci.,54, 140 (2007 )

pCT Challenge #1a: Proton Data rate Tracking and measuring the residual energy of every proton requires fast sensors and fast data acquisition (DAQ). Data Flow math: Assuming 100 protons / 1mm voxel and 180 views requires ~ 7*10 8 protons. With 10 kHz data rate, one pCT scan will take 20 hrs (requiring a very patient patient!). A scan with a proton rate of 2 MHz takes 6 min. N.B. such a scan will deliver a dose of 1.5 mGy. Image Reconstruction To reconstruct images with > 10 7 voxels using ~10 9 protons is NOT trivial. Our reconstruction code is already running on GPU’s in anticipation of the much higher data rates of the future. Hartmut F.-W. Sadrozinski: pCT HSTD8 Dec. 2011 5

Challenge #2 to pCT: Range / Energy Straggling The proton energy loss is not fixed, but is a stochastic process. The straggling error is a function of depth, irreducible when the energy is not measured.  the straggling within the phantom limits the precision of the energy loss measurement. Range counter always encounters the maximum range straggling: the error Geant4 Study: is independent of the WEPL of Range straggling ~ 1% of range phantom (depends on proton energy) ~ 1mm for 100 MeV, ~ 3mm for 200 MeV WEPL Resolution vs. WEPL for different Plate Thickness' (200 MeV Protons) Range Straggling vs. Energy 1 mm 5 3 mm 0.5 2.0% 4 mm 4.8 6 mm 5 mm proj. 6 mm proj. 4.6 0.4 8 mm proj. 1.5% 10 mm proj 4.4 2 ] WEPL RMS [mm] Sigma(R)/R Sigma (R) [g/cm 4.2 0.3 4 1.0% 3.8 0.2 3.6 0.5% 0.1 3.4 3.2 0.0 0.0% 3 0 50 100 150 200 250 0 50 100 150 200 250 300 WEPL [mm] Proton Energy [MeV] WEPL = Water equivalent Path Length (of proton in phantom) Hartmut F.-W. Sadrozinski: pCT HSTD8 Dec. 2011 6

pCT Challenge #2a: useful Proton Rate Efficiency of energy measurement In addition to ionization processes described by the Bethe-Bloch equation, protons undergo processes which remove protons from the peak in the energy spectra useful for the energy determination. Because of non-Gaussian tails, the energy distributions at present are fitted only at the high side, which comes with a loss of precision. With improved modeling of the tails, this might be recoverable. Geant4 Range Counter Data CsI Calorimeter Fraction of Ionization events vs. Energy 1.0 Fraction of Ionization events 0.8 in Polystyrene 0.6 Simulation and data agree well: 0.4 At 200 MeV, only ~60% of the protons entering the CsI data Geant4 Polystyrene phantom will be in the quasi-Gaussian end peak 0.2 Geant4 BaF of the spectrum. 0.0 0 50 100 150 200 250 Hartmut F.-W. Sadrozinski: pCT HSTD8 Dec. 2011 7 Proton Energy [MeV]

Instrument Solutions to the pCT Challenge: Experiment Tracker Energy Detector Proton Energy [MeV] TERA / CERN GEM Range (3mm) + WLSF 100 U. Amaldi et al., NIM A 629 ~100  m + MPPC upgrade (2011) pp 337-344 Firenze / LNS SI SSD Fast crystal calorimeter 68 80  m + P.D. V. Sipala et al., IEEE NSS-MIC 2011, MIC15.S-305 LLU / UCSC / NIU Si SSD CsI + P.D. 100 - 200 F. Hurley et al., subm. to 80  m MEDICAL PHYSICS NIU / FNAL SciFi +MPCC Range (3mm) + WLSF 100 - 200 + MPCC 0.3-0.5 mm under construction LLU /UCSC Si SSD Range (>3mm) + direct 100 - 200 MPCC or “Slim edges” under construction 80  m Polystyrene Calorimeter + PMT Hartmut F.-W. Sadrozinski: pCT HSTD8 Dec. 2011 8

Imaging Results (LLU-UCSC-NIU) B. Colby, D. Fusi, R. Johnson, S. Kashiguine, F. Martinez-McKinney, J. Missaghian, H. F.-W. Sadrozinski, M. Scaringella SCIPP, UC Santa Cruz, CA 95064 USA V. Bashkirov, F. Hurley, S. Penfold, R. Schulte Loma Linda University Medical Center, CA 92354 USA G. Coutrakon, B. Erdelyi, V. Rykalin Northern Illinois University S. McAllister, K. Schubert CSU San Bernardino 2003 2010 Hartmut F.-W. Sadrozinski: pCT HSTD8 Dec. 2011 9

The LLU-UCSC-NIU Prototype Scanner R. W. Schulte, et al., , IEEE Trans. Nucl. Sci., 51,, pp 866, 2004. Optical Interface Photodiode Hartmut F.-W. Sadrozinski: pCT HSTD8 Dec. 2011 10

CT Image Reconstruction 1. WEPL calibration and cut 2. Correction for overlaps in Si tracker 3. Correction matrix with Calorimeter response 4. Angular and spatial binning air lucite 5. Filtered Back Projection and Iterative Algebraic reconstruction 6. MLP formalism for final 2.5 mm polyst. bone reconstruction slice 0.65 mm voxels Reality Check: We accumulated data for this Material Predicted RSP RSP reconstructed from Measurement reconstructed image during 4 hours Polystyrene 1.037 1.035 at 20 kHz trigger rate. Bone 1.70 1.68 This is not acceptable for clinical Lucite 1.20 1.19 applications ! Next development step: Air 0.004 0.05 50x faster pCT scanner Hartmut F.-W. Sadrozinski: pCT HSTD8 Dec. 2011 11 11

LLU-UCSC-CSUSB Head Scanner NIH Grant 1R01EB013118-01 R. Johnson, H. F.-W. Sadrozinski, D. Steinberg, A. Zatserklanyi, V. Bashkirov, F. Hurley, S. Penfold, R. Schulte, S. McAllister, K. Schubert  Increase Size 2x : 40 cm x 10 cm  Improve data throughput 50x:  2MHz sustained proton rate with minimal pile-up  Si sensors are intrinsically fast, built faster readout ASIC and distributed DAQ  Data stream uses local FPGA for data collection, formatting and transmission  Improve speed of energy detector:  CsI calorimeter replaced with faster plastic scintillator  Both range counter and range counter-calorimeter hybrid under test  Polystyrene Range Counter with direct MPPC readout looks very promising (~3x p.e. wrt to WLSF readout?)  Geant4 results on Range Counter with thicker tiles is intriguing  Improve tiling of Si sensors:  Si SSD are attractive since they have low noise at good efficiency, an important factor in a sparse system (no redundant space points)  “slim edges” allow tiling without overlap Hartmut F.-W. Sadrozinski: pCT HSTD8 Dec. 2011 12

WEPL (not Energy!) Detector Choices Hodoscopic Too slow! CsI Calorimeter P.D. Readout 70 plates, Range Counter 4 mm, Direct MCPP readout Polystyrene Scint. (signal 3-5x of 3mm+WLSF) ~ 30 p.e. Range-Calorimeter Hybrid “Bulky”: Proton path 3 Polystyrene 10cmx10cmx40cm + PM 4” 3 - PMT Hartmut F.-W. Sadrozinski: pCT HSTD8 Dec. 2011 13