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RESMDD'02 pCT: Hartmut F.-W. Sadrozinski , SCIPP
SCIPPSCIPP
INITIAL STUDIES on PROTON COMPUTED TOMOGRAPHY USING
SILICON STRIP DETECTORSL. Johnson, B. Keeney, G. Ross, H. F.-W. Sadrozinski, A. Seiden,
D.C. Williams, L. Zhang
Santa Cruz Institute for Particle Physics, UC Santa Cruz, CA 95064
V. Bashkirov, R. W. M. Schulte, K. Shahnazi
Loma Linda University Medical Center, Loma Linda, CA 92354
• Proton Tomography / Proton Transmission Radiography
• Proton Transmission Radiography Data
• Proton Transmission Radiography MC Study
RESMDD'02 pCT: Hartmut F.-W. Sadrozinski , SCIPP
SCIPPSCIPPComputed Tomography (CT)
X-ray tube
Detector array
• Based on X-ray absorption
• Faithful reconstruction of patient’s anatomy
• Stacked 2D maps of linear X-ray attenuation
• Coupled linear equations
• Invert Matrices and find (hopefully) non-malignant structures
RESMDD'02 pCT: Hartmut F.-W. Sadrozinski , SCIPP
SCIPPSCIPP Radiography: X-rays vs. Protons
10
100
1 10 100
Stopping Power for Protons
MuscleBone H2OFat
E [MeV]
0.01
0.1
1
10
100
1000
104
0.001 0.01 0.1 1
X-Ray Absorption Coefficient
Muscle
Bone
Water
Air
Energy [MeV]
[1/cm]
Attenuation of Photons, zN(x) = Noe- x
Energy Loss of Protons, dx
dx
dEE
NIST Data
RESMDD'02 pCT: Hartmut F.-W. Sadrozinski , SCIPP
SCIPPSCIPP Proton Radiography: Density Map
]}[:];/[:{ 2 cmlcmgxdldx
dEdx
dx
dEE
1
10
100
1000
1
10
100
1000
1 10 100 1000
Stopping Power : Density Effect
C
Si
Cu
C
Si
Cu
Energy [MeV]
rho = 9
rho = 2
NIST Data
RESMDD'02 pCT: Hartmut F.-W. Sadrozinski , SCIPP
SCIPPSCIPP Development of Proton Beam Computed Tomography
• Exploratory Study in Proton Radiography– two detector planes– Crude phantom in front
• Experimental Study – two detector planes– water phantom on turntable
• Theoretical Study– GEANT4 MC simulation– influence of MCS and range
straggling– importance of angular
measurements– Optimization of energy
Protonbeam
Simodule 2
Simodule 1
Water phantom
Turntable
Scatteringfoil
RESMDD'02 pCT: Hartmut F.-W. Sadrozinski , SCIPP
SCIPPSCIPP Proton Energy Measurement with LET
Simple 2D Silicon Strip Detector Telescope built
for Nanodosimetry (based on GLAST Design)
2 single-sided SSD
194um Pitch
400um thick
1.3us shaping time
Binary readout
Time-over-Threshold TOT
Large dynamic range
Measure particle energy via LET
RESMDD'02 pCT: Hartmut F.-W. Sadrozinski , SCIPP
SCIPPSCIPP GLAST Front-End Electronics ASIC
Binary Readout: •Low-power (~200uW/channel) •Peaking time ˜ 1.3 ms•Low noise (Noise occupancy <10-5)•Threshold set in every ASIC•Separate Masks for Trigger and Readout in every Channel•Self - Trigger = OR of one Si plane
(1536 channels)
Pulse Charge:Time – over-Threshold on the OR of every Si plane
Distinguish single tracks from two tracks in one strip
Electron Events
Photon Events
RESMDD'02 pCT: Hartmut F.-W. Sadrozinski , SCIPP
SCIPPSCIPP
TOT charge LET!
0
20
40
60
80
100
120
0 50 100 150 200
TOT Measurement vs Charge in MIP'sEffect of Threshold and Voltage
TOT SLACTOT LLUMC
Input Charge [fC]
Charge ~ Time-Over-Threshold (TOT):
Digitization of Position and Energy with large Dynamic Range
Pulse
Threshold
Time-over-Threshold TOT
RESMDD'02 pCT: Hartmut F.-W. Sadrozinski , SCIPP
SCIPPSCIPPProton Energy Measurement with LET
10
100
1 10 100 1000 104
TOT vs. Proton EnergyMeasurement vs. Expectation
TOT & Resolution measuredTOT expected
Proton Energy [MeV]
LLUMCSynchrotron P Beam
GLAST SLAC Test Beam
TOT Saturation
TOT Spectra as for several proton energies
Mean TOT vs. Proton Energy
Good agreement between measurement and MC simulations
RESMDD'02 pCT: Hartmut F.-W. Sadrozinski , SCIPP
SCIPPSCIPPProton Energy Measurement with LET
0.01
0.1
1
10
10 100 1000 104
Resolution of TOT System
LETEnergy
0.01
0.1
1
10
Proton Energy [MeV]
TOT Saturation
0
20
40
60
80
100
0 50 100 150 200 250 300
TOT Measured
ToT measured
y = 964.83 * x^(-0.79073) R= 0.99983
E(MeV)
dTOT/dE = -965*0.79*E-1.79
=-763*E-1.79
TOTTOTE E
TOT
TOT
E 1
TOT Spectra vs. energy
TOT Resolution “~flat”.
Energy Measurement possible where slope dTOT/dE is large
RESMDD'02 pCT: Hartmut F.-W. Sadrozinski , SCIPP
SCIPPSCIPPProton Localisation: M.S. vs. Energy Resolution
0
0.1
0.2
0.3
0.4
0.5
0
0.01
0.02
0.03
0.04
0.05
0 100 200 300 400 500
Proton Energy Error and Mult. Scattering Angle L = 10cm H
2O
E error
M.S. Angle
E [MeV]
With 1000 EventsDetermine Energy Loss to % Level
RESMDD'02 pCT: Hartmut F.-W. Sadrozinski , SCIPP
SCIPPSCIPPExploratory Proton Radiography Set-up
Beam from Synchrotron
30 cm
1 2 - SSD modules
Object
Wax block
1 2 4 3 - SSD detector planes
y x x y
Air
27.3 cm
Air
250MeV 130MeV 60+130MeV
Use Loma Linda University Medical Ctr 250 MeV Proton BeamDegraded down to 130 MeV by Wax BlockObject is Aluminum pipe 5cm long, 3cm OD, 0.67cm ID Very large effects expected, but beam quite non-uniform
RESMDD'02 pCT: Hartmut F.-W. Sadrozinski , SCIPP
SCIPPSCIPPImage !
Subdivide SSD area into pixels1. Strip x strip 194um x 194um2. 4 x 4 strips (0.8mm x 0.8mm)Image given by average TOT or Energy in pixel
RESMDD'02 pCT: Hartmut F.-W. Sadrozinski , SCIPP
SCIPPSCIPPIssues
Features:
Washed out image in 2nd plane
Fuzzy edges
Hole filled partially
Energy diluted at edges and in hole
Migration of events
All explained by Multiple Coulomb Scattering
RESMDD'02 pCT: Hartmut F.-W. Sadrozinski , SCIPP
SCIPPSCIPPLoss of Resolution in Back: Data
RESMDD'02 pCT: Hartmut F.-W. Sadrozinski , SCIPP
SCIPPSCIPPMigration and Energy Dilution in Slice
Data shows increased frequency of hits in boundary of the pipe:the hole and the outside perimeter.These events are associated with a dilution of the energy profile
Hit frequency vs. Location Mean Energy vs. Location
Approx. Beam Profile
Excess Events
Energy lowered
Blurred Edges
RESMDD'02 pCT: Hartmut F.-W. Sadrozinski , SCIPP
SCIPPSCIPPMultiple Scattering: Emigration
Protons scatter OUT OF Target (not INTO). Those have
larger energy loss
larger angles
fill hole
dilute energy
RESMDD'02 pCT: Hartmut F.-W. Sadrozinski , SCIPP
SCIPPSCIPPEnergy Resolution = Position Resolution
Simulation reproduces spread of energy and loss of resolution
Data (LET converted to Energy) GEANT4 MC (LET in SSD)
RMS
RESMDD'02 pCT: Hartmut F.-W. Sadrozinski , SCIPP
SCIPPSCIPPEnergy Resolution
Data:LET converted to Energy
MC:LET in SSD plane
Object Background
RESMDD'02 pCT: Hartmut F.-W. Sadrozinski , SCIPP
SCIPPSCIPPMigration: MC
Dilution by events entering the Object but leaving it before the end
RESMDD'02 pCT: Hartmut F.-W. Sadrozinski , SCIPP
SCIPPSCIPPMC: Loss of Resolution in Back
First Plane, 2cm behind Object
Second Plane, 30cm behind Object
RESMDD'02 pCT: Hartmut F.-W. Sadrozinski , SCIPP
SCIPPSCIPPConclusions
Imaging with protons is working!
GEANT4 program describes the data well
(energy and position resolution, migration)
Issues:
• Energy needs Optimization depending on Target
• Improve resolution with cut on exit angle?
• Investigate independent Energy measurement
• Dose – Contrast - Resolution Relationship to be explored
Next steps: pCT