Development of a camera for imaging of prompt
gamma rays in measurements of proton beam range
P.Busca1,2, C.Fiorini1,2, R.Peloso1,2, M.Basilavecchia3, T.Frizzi3, D. Prieels4,
J. Smeets5*, F. Stichelbaut4, A. Benilov4, F. Roellinghoff4
1Politecnico
di Milano and INFN, Milano, Italy
2XGLab, Milano, Italy
4 Ion Beam Applications S.A., Louvain-la-Neuve, Belgium
5 Department of Nuclear Metrology, Université Libre de Bruxelles, Brussels, Belgium
• Work supported in part by the European Union Seventh Framework Program (FP7/20072013) under grant agreements nos. 241851 (ENVISION) and 264552 (ENTERVISION).
• HICAM gamma detector developed within the EC contract n.LSHC-CT-2006-037737.
• *supported by the Belgian FNRS (aspirant)
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relative dose
Proton therapy
Bragg-peak
g
p
• particle (proton) therapy has a
growing role in cancer treatment.
• possibility to release the maximum
of the dose in the target site,
limiting the dose to normal tissue
depth
• the measurement of the proton beam range in the target is very
important: real range of proton beams in patients may contain
uncertainties of up to 10-15 mm (uncertainties on tissue composition,
density, organ motions, patient positioning, etc).
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One method to measure proton beam range is based on
the measurement of prompt gamma rays (energies up to
10MeV) emitted by excited nuclei during proton irradiation.
(F. Stichelbaut, Y. Jongen, 39th Meet. of the Particle Therapy Co-Operative Group, San Francisco,
October 2003)
p beam
prompt
gs
p beam
target
Monte Carlo
simulation
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Practical concept of a prompt gamma camera which allows
checking in real-time the range of a single pencil beam with a
‘mm’ accuracy
(D. Prieels, J. Smeets, F. Stichelbaut, A. Benilov, J.C. Dehaes, A. Dubus, F. Roellinghoff, 50th Meet. of the
Particle Therapy Co-Operative Group (Philadelphia), May 2011
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HICAM:HIgh resolution gamma CAMera
Research project from European Community
(www.hi-cam.org)
Anger camera principle
scintillator
matrix of
photodetectors
Rigid-Flex
Printed Circuit
cooling systems
bias and
read-out electronic
Silicon
Drift Detectors
- CsI(Tl)
scintillator
- SDDs photodetectors
- 5x6cm2drift
and 10x12cm2 formats
-intrinsic resolution~1mm
- compactness
scintillation entering side
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The HICAM gamma camera development
(R.Peloso, et al., “The HICAM Gamma Camera”, Nuclear Science Symposium Conference Record (NSS/MIC),
2010 IEEE)
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Imaging performances with 99Tc (140keV)
8,7 cm
Resolution, FWHM (mm)
5,0
4,5
4,0
3,5
3,0
2,5
2,0
1,5
1,0
 intrinsic resolution= 0.8mm
0,5
0,0
10,8 cm
corrected for linearity and uniformity
Grid
0
20
40
60
Distance (mm)
LEUHR parallel hole collimator
99Tc
Hole Ø=1mm
Pitch=3mm
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80
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100
Applications of the HICAM gamma camera
50 mm
(P.Busca, et al., “Applications of the HICAM Gamma Camera”, Nuclear Science Symposium Conference
Record (NSS/MIC), 2010 IEEE)
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Modification of the 5x6cm2
HICAM gamma camera
for high-energy (1-10MeV)
imaging
• 1cm thick LYSO scintillator
(h~37%@1MeV, ~22%@5MeV)
• light collection purposely limited (i.e. all
absorbing surfaces) to match readout ASIC
dynamic range (designed for 200keV)
( ~ 5e-/keV, vs. 30ph./keV from LYSO)
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Laboratory characterization
of the camera
1D profile calculation along X:
integration on the Y direction
(1mm bin)
Source: 60Co (1.17MeV, 1.33MeV)
Y
Camera FOV
source
lead block
lead block thickness=3cm
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Area considered for
profile calculation
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X
4
2
Edge profile
x 10
5mm
10mm
15mm
20mm
25mm
30mm
35mm
40mm
45mm
50mm
1.9
1.8
Counts
1.7
1.6
1.5
1.4
1.3
1.2
1.1
10
15
20
25
30
X[mm]
PSD9, Aberystwyth, UK, 15 Sept. 2011
35
40
45
50
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55
Proton range measurements:
the experimental set-up
p beam
slit collimator
opening: 6mm
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electronics
HICAM
camera
g-rays
proton
beam
slit collimator
PMMA target
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Measured energy spectrum
3
10
Counts
LYSO
background
2
10
3-7MeV
range
used in
reconstruction
0
2
4
6
8
10
Energy [MeV]
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12
14
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16
Measured profiles
Profile
Beam energy: 160MeV
Neutron
1800
2500
1600
2000
1400
1200
Counts
Counts
1500
1000
800
1000
500
0
0
20
40
60
80
Width [mm]
100
slits closed
(neutrons + uncorrelated
photons)
600
camera camera camera
position centered position
+ 4cm
- 4cm
400
200
120
0
140
0
20
40
60
80
Width [mm]
100
120
140
Subtraction
subtraction
900
800
central profile
is fitted and
monitored
while moving the
target (and the
Bragg-peak)
700
Counts
600
500
400
300
200
simulation
100
0
0
20
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40
60
80
Width [mm]
100
120
140
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100MeV protons
(preliminary analysis)
-10mm
-8
Fitted edges
x 10
+10mm
0mm
-1mm
-2mm
-3mm
-5mm
-10mm
4
Gammas/Protons
+10mm
3.5
3
2.5
each acquisition:
• 5min.
• 7·1010 protons
2
10
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15
20
25
30
X[mm]
35
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40
45
50
-8
1mm Step
x 10
4.4
Shift accuracy
4.2
4
Fittings
3.8
3.6
reference value
3.4
3.2
X10
X0
X-10
3
2.8
2
20
25
30
Width [mm]
35
40
10
1.5
Theoretical
Measured
8
Accuracy[mm]
Measured Position[mm]
6
4
2
0
1
0.5
-2
-4
0
-6
-8
-0.5
-10
-10
-8
-6
-4
-2
0
2
Theoretical Shift[mm]
4
6
8
10
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-10
-5
0
Theoretical Shift[mm]
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5
10
Precision
reference value
reference position
fitting error
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Precision - 68% confidence interval[mm]
1.3
1.2
1.1
1
0.9
0.8
0.7
0.6
-10
-8
-6
-4
-2
0
2
4
Reference Position[mm]
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6
8
10
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Precision vs. statistics
Precision - 68% confidence interval[mm]
2.5
2
1.5
1
0.5
0
0
10
20
30
40
50
60
Statistics[%]
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70
80
90
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100
7·1010 protons
160MeV protons
-8
(preliminary analysis)
Fitted edges
x 10
+10mm
0mm
-1mm
-2mm
-3mm
-5mm
-10mm
6.5
Gammas\Protons
6
each acquisition:
• 2min.
• 1.7·1010 protons
5.5
5
4.5
10
15
20
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25
30
X[mm]
35
40
45
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50
3
10
Theoretical
Measured
8
2.5
Measured Position[mm]
6
2
Accuracy[mm]
4
2
0
-2
1.5
1
-4
0.5
-6
-8
0
-10
-10
-5
0
Theoretical Shift[mm]
5
-0.5
10
Precision - 68% confidence interval[mm]
Precision - 68% confidence interval[mm]
-5
0
Theoretical Shift[mm]
5
10
15
2.1
2
1.9
1.8
1.7
1.6
1.5
-1
-10
0
1
2
3
4
5
6
Reference Position[mm]
7
8
9
10
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10
5
0
1.7·1010 protons
0
10
20
30
40
50
60
Statistics[%]
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70
80
90
100
Conclusions
• Measurements of prompt gammas correlated to proton range were
successfully made using the HICAM gamma camera
• Although not optimized for 1-10MeV energy range (low efficiency,
low scintillator light collection), satisfactory accuracy and precision
(in the ‘mm’ range) were first measured
Future work
• Further data analysis also to correlate results to dose expected in
patient treatment.
• Measurements to be repeated also with other protons energies
(230MeV).
• Gamma camera to be modified/redesigned to improve efficiency and
speed
PSD9, Aberystwyth, UK, 15 Sept. 2011
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PSD9, Aberystwyth, UK, 15 Sept. 2011
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