Compton Imaging for In-Situ Verification of Particle ...
Transcript of Compton Imaging for In-Situ Verification of Particle ...
Compton Imaging for In-Situ Verification of Particl e Therapy
From Concept to Demonstration
Kai VetterDepartment of Nuclear Engineering, UC Berkeley
Nuclear Science Division, LBNL
2nd Workshop on Hadron Beam Therapy of Cancer
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2nd Workshop on Hadron Beam Therapy of Cancer
Erice, Sicily, Italy
May 20 - 27, 2011
Outline
• What we normally do in Berkeley …
• Goal of gamma-ray imaging for particle therapy (bri ef reminder…)� State-of-the art detection and imaging: PET imaging of ββββ+ emitters
• Other signatures – The potential …� Discrete lines from many levels of several radioiso topes� Bone vs. Tissue� Excitation functions
• Imaging of prompt gamma rays – The challenge …
� Concept and Implementations of Compton imaging
� Advantages and Challenges
� Image reconstruction – limited angle “tomography”
• Status of first simple demonstration experiment – The reality …
• Summary and outlook – The future …
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What we actually do in Berkeley …
Applications
BeARINGNuclear EngineeringUC Berkeley
Applied Nuclear PhysicsNuclear Science DivisionLBNL
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Research
Radiation Detection
A few examples …
• Fundamental and Nuclear Physics� Gamma-ray tracking arrays for nuclear physics appli cations� Ultra-low noise radiation detection
� Neutrino-less double beta decay in 76Ge – MAJORANA PROJECT
� Coherent neutrino-nucleus scattering
• Gamma-ray imaging� Nuclear physics� Nuclear physics� Astrophysics� Nuclear nonproliferation and safeguards� Homeland security
• Fukushima� Research – Nuclear forensics … understand “fallout” and
distribution of radio-tracers from Japan in environ ment …� Education of general public …
� http://www.nuc.berkeley.edu/UCBAirSampling
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Gamma-Ray Imaging: From µµµµm2 to m 2
50µm
Electron-Tracking based Compton imaging� High-resolution CCD w/ 10 µµµµm pixel size
ier
eer
ger
Large-area coded-aperture imaging� Standoff detection � Machine vision and visual and gamma- ray
image information in 3D
2.5 m
Scientific CCD
5
pixe
l ene
rgy
(keV
)
E = 372 keV
50µm
Compton-scatter induced electron track
Full Cone Back-projection
θ
Φ
Partial Cone Back-projection
2.5 m
100 10x10x10cm 3
NaI detectors
3D object tracking
The “Nuclear Street View”
Goal: Detect weak signal out of complex and changing background• Challenge in all imaging applications: Medical imaging, astrophysics, nuclear safeguards, etc.• Merge gamma-ray spectral and location information with visual and object information in 3D!• Create a data base of 3D radiation “backgrounds” (“clickable” objects, returning spectra on 5-
10 m grid
Examples – Cont’d: MISTI!
• MISTI characteristics– Mobile system w/ communication
and GPS capabilities– Optical and infrared cameras– 100 (4”)3 NaI(Tl) detectors + passive
coded aperture– 28 100% HPGe detectors
➥Excellent identification,
MISTI: Mobile Imaging and Spectroscopic Threat Identification, developed by NRL
� Many useful tools and instruments for research and education at UCB-NE!
➥Excellent identification, localization, and object capture
– Extensive and systematic measurements of backgrounds
– Analysis and modeling of background
– Provide background data and models to DNDO and user community
Goal of Gamma-Ray Imaging for Particle Therapy
• Goal: In-vivo treatment verification� Verify actual beam location in object in-situ� Determine range of particles
� Better translation of gamma-ray emission distributi on to dose distribution in 3D
� Reduce systematic uncertainties in comparative stud ies � Reduce systematic uncertainties in comparative stud ies
• Ideally: Instantaneous verification of irradiation field and particle range!� May be even tracking moving beam for dynamic
treatment?
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Approach and Challenges for Imaging
• Approach: Gamma-ray imaging� Observe annihilation radiation from β+ decay: Positron Emission Tomography (PET) of nuclei
decaying by β+ decay resulting in the emission of two 511 keV photons: C-10, C-11, N-13, O-15, …; β+ emitter are either delivered as a beam or are produced in nuclear reactions induced by protons or heavy ions
� Observe “direct” and prompt gamma-ray decay in situ: Single-Photon Emission Computed Tomography (SPECT) by imaging de-excitation of nuclear states populated in nuclear beam-target reactions; Radioisotope-specific gamma-ray imaging (C-12, O-16, Ca-40, …)
• Challenge:• Challenge:� Convert 3D gamma-ray distribution into 3D dose distribution - Modeling� In situ measurements: Very complex and high flux radiation field, particularly for E/u > 100
MeV/u!
� Photons: Many reaction channels, Bremsstrahlung
� Neutrons
� PET: Long half lives of β+ decay, e.g. in C-11; So far, mainly post-treatment measurements, limited spatial resolution and image quality (e.g. limited angle tomography), washout effects
� SPECT: Sensitivity and resolution at 1-7 MeV?
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Count-rate capabilities, neutron-gamma ray discrimination?
Compare Prompt Gamma (PG) w/ PET (MGH)
M. Moteabbed et al, PMB 56 (2011) 1063“Monte Carlo patient study on the comparison of prompt gamma and PET imaging for range verification in proton therapy”
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Signatures: The Potential …
• Discrete lines from many levels of several radioiso topes
• Protons + PMMA
4,E-03
5,E-03
6,E-03
7,E-03
# o
f G
am
ma
s p
er
Pro
ton 100 MeV 200 MeV 300 MeV
GEANT-4.9
C-12, O-16, H
C-12
4439 keV2+
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0,E+00
1,E-03
2,E-03
3,E-03
4,E-03
0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 5 5,5 6 6,5 7 7,5 8 8,5 9 9,5 10
# o
f G
am
ma
s p
er
Pro
ton
Energy (MeV)
4439 keV
0 keV0+
O-16
6049 keV
0 keV
0+
0+
6130 keV
6917 keV7117 keV
3-
2+1-
Signatures: The Potential …
0,001
0,0015
0,002
0,0025
# o
f G
am
ma
s p
er
Pro
ton
200 MeV 100 MeV 50 Mev
5
7 8
• Discrete lines from many levels of several radioiso topes
• Protons + PMMA
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0
0,0005
0,6 1,6 2,6 3,6 4,6 5,6 6,6 7,6 8,6 9,6
# o
f G
am
ma
s p
er
Pro
ton
Energy (MeV)
3 4
6
910
11
131
2
1415
17 1819
7 816
1: .718 MeV
• p + 12C � 2p + n + 10B
2: 1.02 MeV
• p + 12C � 2p + n + 10B
• p + 12C � p + n + 11C
3: 1.4 MeV
• p + 12C � p + n + 11C
4: 1.61 MeV
• n + 12C � p + 12B
5: 2.01 MeV
• p + 12C � p + n + 11C
6: 2.13 MeV
• p + 12C � p + n + 11C
• p + 12C � 2p + 11B
7: 2.23 MeV
• p + 12C � 2p + 11B
8: 2.3 MeV
• p + 12C � 2p + 11B
• p + 16O � n + 2p + 14N
• P + 16O � α + 13N
9: 2.88 MeV
• p + 12C � 2p + 11B
10: 3.33 MeV
• P + 12C � p + n + 11C
• P + 12C � 2p + 11B
11: 4.33 MeV
• p + 12C � p + n + 11C
12: 4.78 MeV
• p + 12C � 2p + 11B
13: 5.02 MeV
• P + 12C � 2p + 11B
14: 5.21 MeV
• p + 16O � 2p + 15N
15: 6.05 MeV
• p + 16O� p + 16O
16: 6.13 MeV
• p + 16O� p + 16O
• p + 16O � 2p + 15N
• P + 16O � p + n + α + 11C
17: 6.48 MeV
• P + 12C � p + n + 11C
18: 6.92 MeV
• p + 16O � p + 16O
19: 7.12 MeV
• p + 16O � p + 16O
Signatures: The Potential …
• Discrete lines from many levels of several radioiso topes
• Protons + PMMA GEANT-4.9
0,0015
0,002
# o
f G
am
ma
s p
er
Pro
ton
100 MeV 200 MeV 300 MeV
DetectorDoppler Broadening
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0
0,0005
0,001
1 1,5 2 2,5 3 3,5 4 4,5 5 5,5 6 6,5 7 7,5 8 8,5 9 9,5 10
# o
f G
am
ma
s p
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Pro
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Energy (MeV)
Signatures: The Potential …
• Bone vs. TissueCan we “track” beam through different materials? GEANT-4.9
Bone
0,004
0,005
0,006
# o
f G
am
ma
s p
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Pro
ton
300 MeV 200 MeV 100 MeV
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0
0,001
0,002
0,003
1 1,5 2 2,5 3 3,5 4 4,5 5 5,5 6 6,5 7 7,5 8
# o
f G
am
ma
s p
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Pro
ton
Energy (MeV)
Signatures: The Potential …
• Bone vs. TissueCan we “track” beam through different materials? GEANT-4.9
Bone0,0008
0,001
# o
f G
am
ma
s p
er
Pro
ton
Acrylic Bone 6 mm Bone with AcrylicTissue(PMMA)
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0
0,0002
0,0004
0,0006
1 1,5 2 2,5 3 3,5 4
# o
f G
am
ma
s p
er
Pro
ton
Energy (MeV)
Signatures: The Potential …
• Excitation Functions …Is there complementary information in the gamma-ray emission ?
• Plot #specific gamma rays vs. location/ depth of em ission GEANT-4.9
Tissue (PMMA)
4.4 MeV gamma ray emission vs. depth
Not just C-12 but also B-10 and others6.050 MeV gamma ray emission vs. depth
Depth of penetration
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5.2 MeV gamma ray emission vs. depth718 keV gamma ray emission vs. depth867 keV gamma ray emission vs. depth
�Plenty of physics to be explored and to be used to improve in-beam verification
Imaging of Prompt Gamma Rays: The Challenge …
• Efficiency and resolution achievable in the imaging of 1 MeV – 7 MeV gamma rays?� Challenge: Highly penetrating and only multiple int eractions in detection
process� Collimator-based systems?
� Very limited sensitivity due to thick absorbers (at tenuation and scatter)
� Optical systems?� Optical systems?
� Limited opening angle, very small FOV, multiple int eractions in detections,…
� Compton imaging?
� In principle, very high angular resolution at MeV ga mma rays possible (<< 1 deg)
� Highest sensitivity of all imaging modality
� BUT:
� Range of secondary particles?
� Efficiency and resolution that can actually be achi eved?
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Concept of Gamma-Ray Tracking based Compton Imaging
2cmE
r1
r2r3
r4
θ
1E
γE
12rr
sourcesource� Gamma rays interact several times with detector via Compton
interaction (e.g. until it is stopped by the photo-electrical effect)
� The interaction pathway is determined from the measured positions and energies of individual interactions (tracking)
� Energies and positions of first two interactions define cone of incident angles (electron path is not measured)
� Cones are projected on plane or sphere (one circle per event) for 2D or into cube (one cone per event) for 3D imaging
( )1
2011cos
EEEcmE−
−=γγ
θThe Compton scattering formula gives θ:
4321 EEEEE +++=γ
source
3 components critical for Compton imaging:
� Position Resolution
(distance between first two interactions)
� Energy Resolution
(energy deposition/ scattering angle)
� Intrinsic Electron Momentum
(scattering angle, gamma-ray energy)
� Tracking allows us to distinguish between
gamma rays and neutrons
Advantages and Implementations
• General Benefits of Gamma-Ray Tracking based Compto n imaging� No collimator-based trade-off between efficiency and resolution� No image degradation due to collimator scattering and penetration� 3D tomographic information with limited view (1-2 views)� Compact and flexible systems possible � Excellent spatial resolution for E > 500 keV� Scalable sensitivity� Differentiation of neutrons and photons by gamma-ray tracking� Large Field-of-View
• Implementations• Implementations� Gas detectors, Scintillators, and Semiconductors… � However, combine high sensitivity and 3D position resolution?
⇒ Semiconductor-based instruments� E.g. Si, Ge, CdZnTe, CdTe, …� Energy resolution: ≤ 2%� Position resolution: Combination of 2D segmentation and signal processing⇒ < 1 mm in 3D (high granularity in 3D)
� Efficiency: Density of solid: 2-7 g/cm3; Volumes: 1 - >100 cm3
� Count rate capabilities? Granularity and digital signal processing helps
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Achievable Spatial Resolution
• Determined by Doppler broadening, energy resolution, and position resolution
• Doppler broadening � Angular resolution of 0.5 deg � Angular resolution of 0.5 deg
translates into < 1mm spatial resolution at distances of up to 20 cm
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The Compact Compton Imager CCI
� 2 HPGe +2 Si(Li) large and segmented detectors in two cryostats & 2nd generation digital DAQ� Si(Li): Each 32+32 strips w/ 2 mm pitch size; 10 mm
thickness; 1.9 keV at 60 keV� HPGe: Each 37+37 strips w/ 2 mm pitch size; 15 mm
thickness; 1.7 keV at 60 keV
� Compact, high-bandwidth and resolution preamplifiers� Fully digital data acquisition system� State-of-the art graphical user interface to setup,
monitor, display, and analyze data.
Assembled CCI-2 instrument
Si+Ge detectors
Photo camera
Pre-amplifiers
monitor, display, and analyze data.� Realtime imaging and gating capabilities
detectors
Dewar 20 cm
Si-II Ge-II Ge-ISi-I
“Static” Tomographic Compton Imaging
• Compton imaging enables 3D or tomographic imaging for objects in near field (Distance < Detector dimension/2)
• Experimental demonstration using CCI-1 and iterative image reconstruction:
4 mm
10 mm2 spherical 113Sn sources (391 keV):Diameter: Each 4 mm
DSSD-Si(Li)
CCI-1
Distance: 10 mm
DSSD-HPGe
3D reconstruction to ~ 1 mm with one view!
Two 113Sn Spheres, Iterative Reconstruction
Maximum Likelihood EM algorithm
z [mm]
x [m
m]
-10 -5 0 5 10 15 20
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0
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Maximum Likelihood EM algorithm
z [mm]
x [m
m]
-10 -5 0 5 10 15 20
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Maximum Likelihood EM algorithm
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Maximum Likelihood EM algorithm
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Experimental ResultMaximum Likelihood Expectation Maximization
X vs. Z
X vs. Y
Maximum Likelihood EM algorithm
y [mm]
z [m
m]
-55 -50 -45 -40 -35 -30 -25
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0
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Maximum Likelihood EM algorithm
y [mm]
z [m
m]
-55 -50 -45 -40 -35 -30 -25
-10
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0
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10
15
20
y [mm]
x [m
m]
-55 -50 -45 -40 -35 -30 -25
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y [mm]
x [m
m]
-55 -50 -45 -40 -35 -30 -25
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X
Y
Z vs. Y
MLEM Reconstruction of line source on background
• Simulated reconstruction results of a 1 mm x 40 mm l ine source on top of background (SNR = 1:5)
Cs-137 line source40 mm long, 1 mm diameter rod
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DSSD-Si(Li)
CCI-1
DSSD-HPGe
� 3D reconstruction of extended source in background w/ ~mm
resolution at 392 keV and 662 keV.
� Imaging at > 2 MeV (4.4 MeV, 6.1 MeV,…) ?
1st Simple Experiment: The (Current) Reality …
• Recent experiment at LBNL to evaluate challenges and opportunities:� Beam: 88” cyclotron to provide “pencil” beam of
protons at 50 MeV� Target: Tissue-equivalent plastic to create
radiation (gamma rays, neutrons, …) + Dosimetry
� Detector: CCI� Challenges: 1mm pencil beam, high-energy
Compact Compton
Imager CCIBeam collimator
(1mm)
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gamma rays, …
Target(1”x1”x2.5” Lucite)
CCI
Reference Ge detector
Measured Photon Spectra from Protons @ 50 MeV in PMM A
Measured Gamma-Ray Spectrum in Reference Ge Detector
C-12: 4.44 MeV
Double-Escape
O-16: 6.30 MeV
• Escape lines – only full-energy deposition is useful for gamma-ray imaging
• Doppler-broadened lines in C-12 due to emission of gamma rays in flight
• Narrow lines e.g. in O-16 due to emission after stopping
• Continuum background
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Single-Escape
Double-Escape • Continuum background
1st Simple Experiment: The (Current) Reality …
�Preliminary, Online Spectrum
�No refined energy calibration
�No event reconstruction yet
• Multiple strip hits
• Charge loss corrections
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Simulated Ge Detector Spectrum
• Protons + PMMA @ 50 MeV• No other materials, collimators, support,…
B10 (p, 3He)B11 (p,2pn)C11 (p,d)
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Energy [MeV]
C-12
O-16
Summary & Outlook: The future …
• Gamma-ray imaging is potentially a very useful tool for beam and dose verification
• PET instruments imaging 511 keV photons are already being used
• Prompt gamma-ray imaging promises additional benefi ts� In-situ imaging – no washout, fast feedback,…� Radioisotope – specific imaging (C, O, N, Ca, …)� Excitation function measurements (additional handle on activity-dose
conversion)� Semiconductor-based Compton imaging promises high s patial
resolution (<1mm) with compact systems and limited views
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Acknowledgements
• UC Berkeley� Joe Miller, Daniel Bond, Department of Nuclear Engineering
• LBNLLucian Mihailescu, Nuclear Science Division� Lucian Mihailescu, Nuclear Science Division
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Questions?
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Comparison PG vs. PET
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Gamma-ray fluxes… (very preliminary)
• Is there enough or too much information?
• For example, 200 Gp (or 2x10 11 protons)/ treatment in 60 s, or about 10 5 p/ mm 3 /min
• Too much?� E.g. ~20% of protons at 200 MeV produce photons resu lting ~ MHz in
detectordetector
• Enough ?� E.g. ~ 1% of protons at 200 MeV produce full energy detection of
usable gamma rays at ~ kHz
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Prompt emission spectra
C-12
N-14
Relative gamma-ray production as a function of proton energy for carbon (triangle), nitrogen (square), oxygen (diamond) and calcium
(circle). Gamma-ray production for all proton energies is normalized to the maximum production for each element.
O-16
Ca-40
JC Polf et al. Phys.
Med. Biol. 54
(2009) 731–743
Proton beams – difference between gamma-ray activity and dose
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Positron emission of C -12 beams
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