Transcript GLAST Proposal Review - Santa Cruz Institute for Particle
2002 IEEE NSS/MIC pCT: Hartmut F.-W. Sadrozinski , SCIPP
Towards Proton Computed Tomography
L. R. 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 Energy Loss in Matter • Proton Tomography / Proton Transmission Radiography • Proton Transmission Radiography Data • Proton Transmission Radiography MC Study
2002 IEEE NSS/MIC pCT: Hartmut F.-W. Sadrozinski , SCIPP
Computed Tomography (CT)
• • • • •
CT: 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 reconstruct z dependent features
• •
Proton CT: replaces X-ray absorption with proton energy loss reconstruct mass density ( distribution
r)
distribution instead of electron X-ray tube Detector array
2002 IEEE NSS/MIC pCT: Hartmut F.-W. Sadrozinski , SCIPP
Radiography: X-rays vs. Protons
Attenuation of Photons, Z N(x) = N o e -
x Energy Loss of Protons,
r D
E
dE dx dx
r
dE
D
l dx
10 4 100 [1/cm] 1
X-Ray Absorption Coefficient
100 Bone Muscle H2O Fat dE/dl [MeV/cm] 10
Stopping Power for Protons Bethe-Bloch
dE dl
r
dE dx
Low Contrast:
Dr
= 0.1 for tissue, 0.5 for bone
Bone Muscle H2O Fat 0.01
1 10 100 X-Ray Energy [keV] 1000 1 10
NIST Data
100 Proton Energy E [MeV] 1000
Measure statistical process of X-ray removal Measure energy loss on individual protons
2002 IEEE NSS/MIC pCT: Hartmut F.-W. Sadrozinski , SCIPP
Negative Slope in the Bethe-Bloch Formula
300
•
Relatively low entrance dose
(plateau) •
Maximum dose at depth
(Bragg peak) •
Rapid distal dose fall-off
•
RBE close to unity 200 Proton Energy [MeV] 100 0 0 Proton Energy Loss in H 2 O 10 Energy Deposit in 1mm [MeV/mm] 5 E = 130 MeV E = 250 MeV 10 20 30 Water Depth [cm] 40 Imaging Treatment 50 0
2002 IEEE NSS/MIC pCT: Hartmut F.-W. Sadrozinski , SCIPP
Protons vs. X-Rays in Therapy
Protons:
•
Energy modulation spreads the Bragg peak across the malignancy X-rays:
•
High entrance dose
•
Reduced dose at depth
•
Slow distal dose fall-off leads to increased dose in non-target tissue
2002 IEEE NSS/MIC pCT: Hartmut F.-W. Sadrozinski , SCIPP
Milestones of Proton Computed Tomography
• •
R. R. Wilson (1946) Points out the Bragg peak, defined range of protons A. M. Cormack (1963) Tomography
• • • •
M. Goitein (1972) 2-D to 3-D, Simulations A. M. Cormack & Koehler (1976) Tomography,
Dr
0.5 %
•
K. M.Hanson et al. (1982) Human tissue, Dose advantage U. Schneider et al. (1996) Calibration of CT values, Stoichiometric method T. J. Satogata et al. (Poster M10-204) Reduced Dose of Proton CT compared to X-Ray CT
2002 IEEE NSS/MIC pCT: Hartmut F.-W. Sadrozinski , SCIPP
What is new in pCT ?
•
Increased # of Facilities with gantries etc.
See the following talk by Stephen G. Peggs)
•
2 Ph.D. Theses at PSI and Harvard Cyclotron (U. Schneider & P. Zygmanski)
•
Existence of high bandwidth detector systems for protons
– – – –
semiconductors high rate data acquisition ( > MHz) large-scale (6”wafers) fine-grained (100’s um pitch)
•
Concerted simulation effort
– – – –
Exploitation of angular and energy correlations Support of data analysis Optimization of pCT set-up (detector, energy, ..) Dose calculation
2002 IEEE NSS/MIC pCT: Hartmut F.-W. Sadrozinski , SCIPP
Potential of Proton CT: Treatment Planning
X-ray CT use in proton cancer therapy can lead to large uncertainties in range determination Range Uncertainties (measured with PTR)
> 5 mm > 10 mm > 15 mm Schneider U. & Pedroni E. (1995), “Proton radiography as a tool for quality control in proton therapy,” Med Phys. 22, 353.
Alderson Head Phantom
Proton CT can measure the density distribution needed for range calculation.
There is an expectation (hope?) that with pCT the required dose can be reduced.
2002 IEEE NSS/MIC pCT: Hartmut F.-W. Sadrozinski , SCIPP
Low Contrast in Proton CT
Sensitivity Study: Inclusion of 1cm thickness and density
r
at midpoint of 20cm H 2 O 0.8
0.6
Energy Loss [MeV/mm] 0.4
0.2
1
r r*
l [g/cm 2 ] 1.0
1.1
1.5
2.0
Energy [MeV] 164.1
163.6
161.5
158.9
Range [cm] 38.2
38.1
37.7
37.2
TOF [ps] 1309 1311 1317 1325 200 Proton Energy [MeV] 150 0 Energy Loss in Water
dE (250) dE (250)+1.1
dE (250)+1.5
dE (250)+2
Proton Energy
r 1.0
1.1
1.5
2.0
5 10 15 Depth in H 2 O [cm] 20 25
2002 IEEE NSS/MIC pCT: Hartmut F.-W. Sadrozinski , SCIPP
Requirements for pCT Measurements
Tracking of individual Protons requires Measurement of:
• • • •
Proton location to few hundred um Proton angle to much better than a degree Multiple Coulomb Scattering
MCS
1 o Average Proton Energy
•
Issue: Dose D = Absorbed Energy / Mass N/A = Fluence
( for Voxel with diameter d = 1mm 10 5 protons of 200 MeV = 7 [mGy]) •
In order to minimize the dose, the final system needs the best energy resolution! Energy straggling is 1- 2 %.
CMS
13 .
6
MeV
p z
E
E N l
/
X
0 D N A
dE dx
E
1 %
2002 IEEE NSS/MIC pCT: Hartmut F.-W. Sadrozinski , SCIPP
Dose vs. Voxel Size for pCT Measurements
Trade-off between Voxel size and Contrast (
Dr
) to minimize the Dose Define voxel of volume d 3 Dose in voxel = D v Take n =20cm/d settings Total dose D = n* D v Require 3
Significance
D ~ D 2 r
E
2
d
5
pCT: Contrast - Voxel Size - Dose 200 MeV Protons, 3Stdv.
1 Dose [mGy] 0.01
0.0001
10 -6 0.01
Voxel Diameter
d=5mm, Si d=2mm, 2% d=5mm, 2% d=1cm, 2%
0.1
1 Density Difference [g/cm 3 ] 1 0.01
0.0001
10 10 -6
2002 IEEE NSS/MIC pCT: Hartmut F.-W. Sadrozinski , SCIPP
Studies in Proton Computed Tomography
Collaboration Loma Linda University Medical Center – UC Santa Cruz
•
Exploratory Study in Proton Transmission Radiography
– – –
Silicon detector telescope Simple phantom in front Understand influence of multiple scattering and energy resolution on image
•
Theoretical Study (GEANT4 MC simulation)
– –
Evaluation of MCS, range straggling, and need for angular measurements Optimization of energy
2002 IEEE NSS/MIC pCT: Hartmut F.-W. Sadrozinski , SCIPP
Exploratory Proton Radiography Set-up
Proton Beam from Loma Linda University Medical Ctr @ 250 MeV Degraded down to 130 MeV by 10” wax block Object is aluminum annulus 5 cm long, 3 cm OD, 0.67 cm ID Very large effects expected, x =
r
*l = 13.5 g/cm 2 Traversing protons have 50 MeV, by-passing protons have 130 MeV Silicon detector telescope with 2 x-y modules: measure energy and location of exiting protons Wax block Air Air
Object
Beam from Synchrotron 30 cm 27.3 cm y x
Si Modules
x y
250MeV 130MeV 50 + 130MeV
2002 IEEE NSS/MIC pCT: Hartmut F.-W. Sadrozinski , SCIPP
Silicon Detector Telescope
Simple 2D Silicon Strip Detector (SSD) Telescope of 2 x-y modules built for Nanodosimetry
•
2 single-sided SSD / module
measure x-y coordinates •
GLAST Space Mission developed SSD
194 m pitch, 400 m thickness
6.4 cm
•
GLAST Readout
1.3 s shaping time Binary readout Time-over-Threshold TOT Large dynamic range
5 x 64 channels
2002 IEEE NSS/MIC pCT: Hartmut F.-W. Sadrozinski , SCIPP
Time-Over-Threshold ~ Energy Transfer
Digitization of position (hit channel) and energy deposit (TOT)
Time-over-Threshold TOT Pulse Threshold
TOT
charge
LET 120 100 80 TOT [us] 60 40 20 0 0 TOT Measurement vs Charge 50 100 Input Charge [fC] 150 200
2002 IEEE NSS/MIC pCT: Hartmut F.-W. Sadrozinski , SCIPP
Calibration of Proton Energy vs. TOT
Good agreement between measurement and MC simulations 100 TOT vs Proton Energy Measurement and Expectation TOT Saturation ToT measured TOT expected TOT [us] 0.4
0.3
0.2
0.1
0 10 Proton Energy Resolution 100 Proton Energy [MeV] 0.4
0.3
0.2
0.1
0 1000 10 10 LLUMC Synchrotron P Beam GLAST SLAC Test Beam 100 1000 Proton Energy [MeV] 10 4 Derive energy resolution from TOT vs. E plot
2002 IEEE NSS/MIC pCT: Hartmut F.-W. Sadrozinski , SCIPP
Image of Al Annulus
Subdivide SSD area into pixels 1.
2.
Strip x strip 194um x 194um 4 x 4 strips (0.8mm x 0.8mm) Image corresponds to average energy in pixel
2002 IEEE NSS/MIC pCT: Hartmut F.-W. Sadrozinski , SCIPP
Energy Resolution => Position Resolution
Slice of average pixel energy in 4x4 pixels (need to apply off-line calibration!)
Hole “filled in” “Fuzzy” Edges
Clear profile of pipe, but interfaces are blurred
2002 IEEE NSS/MIC pCT: Hartmut F.-W. Sadrozinski , SCIPP
Multiple Scattering: Migration
Image Features: Washed out image in 2 nd plane (30cm downstream) Energy diluted at interfaces (Fuzzy edges, Large RMS, Hole filled in partially) Migration of events are explained by Multiple Coulomb Scattering MCS Protons scatter OUT OF target (not INTO). Scatters have larger energy loss, larger angles, fill hole, dilute energy
2002 IEEE NSS/MIC pCT: Hartmut F.-W. Sadrozinski , SCIPP
GEANT4 MC: Use of Angular Information
Si Telescope allows reconstruction of beam divergence and scattering angles Select 2 Areas in both MC and Data A = inside annulus : Wax + Al B = outside annulus : Wax only Angular distributions well understood
2002 IEEE NSS/MIC pCT: Hartmut F.-W. Sadrozinski , SCIPP
GEANT4 MC: Migration
Beam profile in slice Migration out of object Energy of protons entering front face Protons entering the object in front face but leaving it before the rear face
2002 IEEE NSS/MIC pCT: Hartmut F.-W. Sadrozinski , SCIPP
GEANT4 MC: Use of Angular Information
Angular Cut at
MCS of the Wax
Energy Profile before (after ) Angle Cut
Less Migration Sharp Edges ( Energy Average ) Sharp Edges ( Energy RMS )
Energy RMS before (after ) Angle Cut
Angular cut improves the contrast at the interfaces
2002 IEEE NSS/MIC pCT: Hartmut F.-W. Sadrozinski , SCIPP
Conclusions
• • • •
Present status of pCT: Long tradition, increased interest with many new proton accelerators (see next talk by Stephen G. Peggs) pCT will be useful for treatment planning (reconstruction of true density distribution) Potential dose advantage wrt X-rays ( see Poster M10-204 by Satogata et al. ) Use of GEANT4 simulation program aids in planning of experiments (correlation of energy and angle, “migration”) (see Poster M6-2, L. R. Johnson et al.)
• • •
Our future plans: Optimization of beam energy Investigation of optimal energy measurement method Dose – contrast - resolution relationship on realistic phantoms