Treatment planning dosimetric parameters for a 90Y coil source used in intravascular brachytherapy
Dosimetric characterization with 62MeV protons of a silicon-segmented detector for 2D dose...
Transcript of Dosimetric characterization with 62MeV protons of a silicon-segmented detector for 2D dose...
Dosimetric characterization with 62 MeV protons of a silicon segmented detector
for 2D dose verifications in radiotherapyfor 2D dose verifications in radiotherapy
C. Talamonti
M. Bruzzi,M. Bucciolini, L Marrazzo D MenichelliL. Marrazzo, D. Menichelli
University of FlorenceINFN Florence
G.A.P. Cirrone, G. CuttoneINFN-LNS
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INFN LNS
Outline
MAESTRO
Ou e
• MAESTRO• Detector• Dosimetric characterization with protons
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Clinical dosimetry in radiotherapy is well known matter but highconformal radiotherapy modalities (IMRT, Stereotactic treatmentswith photons and protons IMPT) pose problems due to the smallwith photons and protons, IMPT) pose problems due to the smallradiation fields with high dose gradients, to the variation in spaceand time of the dose rate and to the variation in space and time ofth b tthe beam energy spectrum.
IMRT
IMPT
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IMRT
45,000 4540,000 patients
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22 PT centers
15 000
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PT center under operation10,000
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1950 1960 1970 1980 1990 2000 20100
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1950 1960 1970 1980 1990 2000 2010
In the framework of the European IntegratedIn the framework of the European Integratedproject MAESTRO( h d d Ad d i f Si l i d(Methods and Advanced Equipment for Simulation and Treatmentin Radio-Oncology, no. LSHC-CT-2004-503564),a dosimetric detector adequate for 2D pre-treatment dose verifications was developed.
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• The research is focused on point, 2D and 3Ddosimeters.
• Diamond sensors for miniature dosimeters • Optical Fibre Dosimeter
• 2D large area ionisation planar silicon detectors • Gas detectors • Pixel Ionisation Chambers for Proton therapy & IMRT • Large area thermoluminescent dosimeters
• Gel dosimetry optical readout systems by optical computed tomography • Three-Dimension Dosimetry with Plastic
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lid i l d dMAESTRO 2D validation protocol and procedures
1) Detector working in integration mode9) Linearity vs. absorbed dose
Requirement: < 1%in 0 1 2000 cGy rangein 0.1- 2000 cGy range
2) Spatial resolution: sensor sizeRequirement: 1-2 mm (photons)
1 mm (protons)
10) Background signalRequirement: < 0.1% of radiation induced signal
3) Spatial resolution: granularityRequirement: 1-2 mm (photons)
1 mm (protons)
11) Energy dependenceRequirement: < 1%
photons in 4–25 MV rangeProtons in 20-200 MeV range
12) LET D d4) Dose rate dependence Requirement: < 1%
in the range 1- 400 cGy/min
12) LET DependenceRequirement: < 1%
5) Short-term precisionRequirement:
response repeatability < 0.5%13) Water equivalence
6) Fast detector responseRequirement: detector able to follow the linac output variation
14) Angular dependenceRequirement: < 1%equ e e t: detecto ab e to o ow t e ac output va at o equ e e t: %
7) Detector areaRequirement: ≥ 20 cm x 20 cm
15) Transparency for beam monitoring devices
8) Radiation hardness 16) Reproducibility
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8) Radiation hardnessRequirement: as much as possible (different element of matrix)
Requirement: < 1%
The requirements on the idealqdetector for dose evaluation inradiotherapy are such that onlyfew solutions exist but no one hasfew solutions exist but no one hasthe combined performance onhigh sensitivity, small dimensions
445 silicon diodes
22X22 cm2 diodes Pitch 1.0 cm
and separation distance, tissueequivalence with high precisionresponse and perfect stability 1024 cylindricalresponse and perfect stability.
729
1024 cylindrical ionization chambers
24 x 24 cm2
ionization chambers
27x27 cm2
Pitch 10 mm
Pitch 7.5mm
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Pitch 10 mm
Our goal was to develop a device adequate for 2Dg p qpre-treatment in phantom dose verifications inconformal radiotherapy on a beam-by-beam basis.py yAccurate determination of the 2D absorbed dose
distribution requires detectors with high spatial
resolution, a response independent of the dose rate,eso ut o , a espo se depe de t o t e dose ate,
of the energy, fast, stable in time, with a good
linearity and high dynamic range.
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Italian patent N FI2006A000166
It is a modular detector, based on a monolithic siliconsegmented sensor, with a n-type implantation on an epitaxialg , yp p pp-type layer. Each pixel element is 2x2 mm2 and thedistance center-to-center is 3 mm. The sensor is composedof 21x21 pixels Area 6 29x6 29 cm2
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of 21x21 pixels. Area 6.29x6.29 cm2.
Attractives of Si:
a) linear relationship between photon energy and e/h pairs; b) hi h iti it (Si 3 6 V/ i ) ll ti l hi hb) high sensitivity (Si ~3.6 eV/pair) small active volume high spatial resolution; c) well developed technology for the production of segmentedc) well developed technology for the production of segmented monolithic planar detectors.
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Commercial single-pad Si dosimeters:
S α L = √(D τ) , D diffusion coefficient , τ minority carrier lifetime:
1/τ = 1/τ0 + K D
Material Problems and solutions
Commercial single-pad Si dosimeters: dependence of sensitivity on dose.
Key idea: to fix the pixel active 500t
/τ /τ0
Key idea: to fix the pixel active volume by limiting its lateral size and depth to values shorter than diffusion length after irradiation at the higher 300
400n-type
p-type
y [n
C/G
y]
g goperative dose.
Sensitivity of silicon is quite high, and 100
200
Sen
sitiv
ity
y gthe subsequent reduction in signal strength is of no concern. 0 2 4 6 8 10 12 14
0
Dose [KGy] G Rikner et al Phys Med Biol 28 1983 1261 12670In practice: lateral size limited by a
guard ring structure; active thickness limited by implanting the pixels upon
50 thi k it i l l
G.Rikner et al.Phys. Med. Biol. 28, 1983, 1261-12670
Standard Si dosimeters Pre-irradiation up to 10kGy
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a 50 μm thick epitaxial layer.p y
Frequent Calibration
-Irradiation of test samples with 6 MeV
Choice of Si material and pixel geometry
pelectrons.-Comparison of samples of different materials(Cz, FZ, epi), resistivity and type (n/p).-p-type Epi diodes show the higher radiationhardness in terms of sensitivity reduction.
1 1
-Measurements on p type, 50 μm thick, epi samples with a different pad to guard-ring distance X.A l d i (20 ) l d th
1,0
1,1
Sen
sitiv
ity 10 μm 20 μm 50 μm 100μm 200 μm 500 μm No GR
-A close guard ring (20 μm) excludes the contributions from the lateral area diffusion.-Sensitivity slightly decreases for Doses up to
0 8
0,9
Nor
mal
ised
S
1.5 kGy (3.5 % for X=10 μm ) and it is almost constant up to 10 kGy (within 1.8%).0 2 4 6 8 10
0,8N
Accumulated Dose [kGy]
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Epitaxial silicon devices for dosimetry applications , Bruzzi M, Bucciolini M, Casati M., Menichelli D., Talamonti C., Piemonte C., Svensson BG., Appl. Phys. Lett. 90, 172109 2007
Design and production of silicon modules
441 Si n+p diodes 50 µm epi layer on p MCz441 Si n+p diodes, 50 µm epi layer on p MCz. Active area: 6.29x6.29 cm2.Segmentation: 21x21 pixel (2×2 mm2 , 3 mm pitch). Overmetal strips to 441 pads along one single sideOvermetal strips to 441 pads along one single side.Diffused guardring structure at 20 µm from pads.DC coupling.
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9-modules design:A single module cut from each wafer. Nine modules will be used to cover an area of about 20×20 cm2. System complexity: ~4k channels
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441ch TERA-based prototype
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Device State Completed /to be completed by:
Silicon Module Designed, Aug. 2005(15 6x6 samples from IRST) manufactured and
tested
441 ch prototype with discrete l t i
Assembled and tested March 2006electronics
ASIC choice and testing Done June 2006
441 ch prototype Design Done Sept. 2006with integrated electronics
Part manufacturing Done Jan. 2007
Assembling Done May 2007
Debug O In progress May 2007Debug O In progress May 2007
Beam test X To be done Sept. 2007
Full detector4k h
Design X Done, in part during 20084k ch Part manufacturing OX In progress, in part
Assembling X To be done
Debug X To be done
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Debug X To be done
Beam Test X To be done
Dosimetric characterizationPh t bPhoton beam
The module was irradiatedwith 6 10 25 MV photonwith 6, 10, 25 MV photonbeams from Precise LINAC(ELEKTA)(ELEKTA)
RD07 International Conference on Large Scale Applications and Radian hardness of Semiconductor detectorsFlorence, June 27-29 2007
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The dosimetric characterization has beenperformed following the protocol and theperformed following the protocol and theprocedures defined inside MAESTRO Project.
Almost all the channels exhibit performanceswithin the project specifications repeatability <0.5%, reproducibility < 1%, deviation fromlinearity < 1%, dose rate dependence < 1%.
Preliminary results of dosimetric characterization of a silicon segmented detector for 2D dose verifications in radiotherapy, C. Talamonti, M. Bruzzi, M. Bucciolini, L. Marrazzo, D. Menichelli Nucl.Instrum.Meth A (in press).
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Dosimetric characterization: P E i lProton Experimental setup
The module wasirradiated with 62MeV protons for
di l li ti tmedical applications atINFN-LNS Catania
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During one irradiation several∑
×≡ nini
QVnFq 1
gsamples (q) are acquired (time>>T=205 ms). They are summedoff line (Q)
∑=i
ninj qQ
off line (Q).
The signal is expressed in C0.7
0.8 channel nj=1 j=2 j=3
The signal is expressed in C,assuming the integration on aconventional capacity of 1nF. 0.4
0.5
0.6
ca q
(nC
)
j=1 j=2 j=3q (n
C)
Fluctuations during irradiationsbecause of noise of the device and 0.1
0.2
0.3caric
char
ge q
because of noise of the device anddose rate instability of the beam. 0 500 1000 1500 2000 2500
0
campione index isample
c
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2 70 60
70
80y profile for the 20 mm diameter proton field
4
6
840
50
60
20
30
40
50
Sig
nal (
nC)
row
s 10
12
1420
30
40 Signal (nC
) 0 10 20 30 40 50 600
10
20
y profile (mm)
14
16
18
20 -10
0
10
60
70
80x profile for the 20 mm diameter proton field
Fi ld i 20 di tcolumns
5 10 15 20
20 10
30
40
50
60
Sig
nal (
nC)
Field size 20 mm diameter0 10 20 30 40 50 60
0
10
20
x profile (mm)
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RepeatabilityRepeatability
Dose rateRepeatability
Dose rate(Gy/min) σ%
(%)N0.5(%)
• σn< 0.5% for most of the channels in the radiation field
0.18 0.8 58%
2.5 0.2 100%
if RN ≥2.5 Gy/min. 6.8 0.2 100%
14 0 5 70%14 0.5 70%
MAESTRO requirement: σ% < 0.5 %
N is the percentage of pixels with σ(%) < 0 5%
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N0,5 is the percentage of pixels with σ(%) < 0.5%.
Channel no.325, linearity
Linearity Nominal
2500
3000
3500
4000
C)
, y
Dose rate14 Gy/min
Nominal dose rate(Gy/min)
<dn>n(%)
N1(%)
<an>n(nC/cGy)
<δan>n(nC/cGy)
500
1000
1500
2000
Sig
nal(n
C
14 1 65 0.723 0.002
2.5 1 57 0.895 0.0010 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
0
Dose (cGy)
400
450Channel no.325, linearity
Dose rateRange 20- 5000 cGy
200
250
300
350
Sig
nal(n
C)
2.5 Gy/min
MAESTRO requirement: d<1 %0 50 100 150 200 250 300 350 400 450 500
0
50
100
150
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Dose (cGy)
Output factors (protons)
100
120
80
100
or (%
)
Markusscanditronix diode
40
60
Out
put f
act scanditronix diode
GAFTLDMAESTRO
20
O MAESTRO
00 5 10 15 20 25 30
Collimator diameter (mm)
RD07 International Conference on Large Scale Applications and Radian hardness of Semiconductor detectorsFlorence, June 27-29 2007
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Depth dose measurements (protons)
1.2
1.4
Spread Out Bragg Peak
1
CATANA:
0.6
0.8
Sig
nal (
nC) C N :
62 MeV proton beam
M t i PMMA
0.2
0.4Measurements in PMMA
0 5 10 15 20 25 300
0.2
depth (mm)
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p ( )
di i dRadiation damagePhotons:
The device was exposed to a radiation dose of about 0.5 kGy and the reduction in
sensitivity is about 2%. This result agrees with the results of experiments performed
on single diodes of the same materials.
Considering the results obtained with the
single diode, we expect that the sensitivity g , p y
still decreases with the accumulated dose.
Epitaxial silicon devices for dosimetry applications , Bruzzi M, Bucciolini M, Casati M., Menichelli D., Talamonti C., Piemonte C., Svensson BG., Appl. Phys. Lett. 90, 172109
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Piemonte C., Svensson BG., Appl. Phys. Lett. 90, 172109 2007
P tProtons:The device was exposed to a radiation dose of about 0.6 kGy and the reduction
in sensitivity is about 1,5%.
We still haven’t performed any tests on proton damage of the single diode. We
can just compare this result with the electron curve and this result agrees with
the results already shown. After a sensitivity decrease<of about 7% observed
up to 1.5 kGy, its sensitivity remains constant within 1.8% up to 10 kGy.
The sensitivity should still decrease with the accumulated dose up to 1.5 kGy
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2
1 6
1.8
)
slope=(2.0 +- 0.2) pA/Gy
mar. '07
1.4
1.6rk
cur
rent
(nA
)
1
1.2dar
may '07
0.6
0.8
0 50 100 150 200 250 300 3500.4
dose (Gy)
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C l iConclusions
• We described the device developed inside the MAESTRO projectMAESTRO project
• It is suitable for measurements with proton beams also with low energy protons that correspond to the highestwith low energy protons that correspond to the highest LET.
• Next step is to characterize the new prototype with a• Next step is to characterize the new prototype with a discreet electronics
• We are also planning to performer study of radiation• We are also planning to performer study of radiation damage with proton beam on the single diode
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