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The author research is supported by the European
Community under under the contract
G1RD-CT-2001-00561
A NOVEL b PARTICLES SILICON DOSIMETER
Chiara Cappellini University of Insubria-Como
IEEE NSS-MIC conference Rome, 18/21 October 2004
Chiara Cappellini University of Insubria-Como
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SUCIMA PROJECT

• Sucima, Silicon Ultrafast Camera for b and g
  sources In Medical Applications, is a research
  project approved by the European Commission
  within the 5th framework program
• The project is coordinated by University of
  Insubria and eleven partners from five European
  countries are involved
• The main goal of the project is the development
  of a novel type of Silicon real time, high
  granularity, monolithic, pixel dosimeter to be
  used in medical application
• Two are the major application foreseen by the
  collaboration

Hadrotherapy
IV-Brachytherapy
IEEE NSS-MIC conference Rome, 18/21 October 2004
Chiara Cappellini University of Insubria-Como
http//sucima.dipscfm.uninsubria.it
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THE HYBRID SOLUTION
The final SUCIMA sensor have been manufactured in
CMOS and SOI monolithic technology
CMOS
Brachytherapy
Dr. Grzegorz Deptuch Photodetectors and
Radiation imaging N41-2.
SOI
Prof. Wojtek Kucewicz New Solid State Detectors
N28-2.
In the following..
Dr. Laura Badano Beam Instrumentation N46-3
Hadrotherapy
In order to have an early feed-back from the
medical end users hybrid prototypes have been
developed
IEEE NSS-MIC conference Rome, 18/21 October 2004
Chiara Cappellini University of Insubria-Como
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THE SENSOR

• Produced by HAMAMATSU on AGILE design
• Dimension 9.5 x 9.5 cm2
  Thickness 410mm
• 768 strips 121 ?m pitch
• Leakage current 0.1nA/strip _at_ 80 V (full
  depletion)

Barbiellini, G. and others, Nucl. Instr. and
Meth. A490 (2002) 146

• 6x128 channels, pitch100 mm
• 4 different gains, integrating
• Range 405, 41000 fC (110-11000 mip)
• double samplehold -gt no dead-time

IEEE NSS-MIC conference Rome, 18/21 October 2004
Chiara Cappellini University of Insubria-Como
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SENSOR QUALIFICATION
SILICON STRIPS SILICON STRIPS
STABILITY 99.8
REPEATABILITY 98.5
LINEARITY gt98
UNIFORMITY 97

• Infra red laser (l 1024 nm) on a mm 3D movement
  station
• Sensor qualification in terms of stability,
  repeatability, linearity and uniformity of
  response

IEEE NSS-MIC conference Rome, 18/21 October 2004
Chiara Cappellini University of Insubria-Como
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ASSESSMENT OF RELATIVE DOSIMETRY
Acquisition of DDC in PMMA phantoms and
comparison with qualified dosimeters MC
Yexp(AxB) Yexp(AxB) Yexp(AxB)
A B
Si - 0.82?0.02 1.89?0.09
Gaf - 0.87?0.04 2.08?0.26
Opt. - 0.77?0.02 1.75?0.04
MC -0.82?0.005 1.86?0.02
According to the AAPM tg60 prescriptions
PMMA
90Sr/Y
A 1 mCi
IEEE NSS-MIC conference Rome, 18/21 October 2004
Chiara Cappellini University of Insubria-Como
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ASSESSMENT OF RELATIVE DOSIMETRY
Acquisition of azimuthal profiles in PMMA
phantoms and comparison with qualified dosimeters
?in 0,74 mm ?ext 1,19 mm ?source 0,64
mm ?tunnel 1,50 mm 85 ?m of fall off source ?
10 dishomogenity
IEEE NSS-MIC conference Rome, 18/21 October 2004
Chiara Cappellini University of Insubria-Como
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TOWARDS ABSOLUTE DOSIMETRY From strips to
pixels
To fully qualify the system it is necessary to
prove the possibility of absolute dosimetry, i.e.
to directly measure the dose from the energy
released in the sensor. But using strip detector,
the problem is how to convert the charge
integrated along one strip to that released in
each point of the sensor!
1D
2D
To prove the principle, the idea is to use the
signal information from the strips and the
geometrical information one can get from
GafChromic films
IEEE NSS-MIC conference Rome, 18/21 October 2004
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1st step digitising the Gaf
A.U.
pixel rows
silicon strips
From the 2D dose map it is possible to get the
integrated dose along one dimension. This
information corresponds to the one returned by
the strips
D 17x3-23.96x224.94x-0.3941
IEEE NSS-MIC conference Rome, 18/21 October 2004
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3rd step scaling factor
95 of the fitted function peak value 20 of
the signal ? statistically significant value
A
B
define a length along which we assume a uniform
dose release
and a scaling factor for the strips outcome
IEEE NSS-MIC conference Rome, 18/21 October 2004
Chiara Cappellini University of Insubria-Como
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4th step scaling the strips outcome
Finally we get the released DOSE !!!
? 3
IEEE NSS-MIC conference Rome, 18/21 October 2004
Chiara Cappellini University of Insubria-Como
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The Dose Rate

• Still a systematic error
• Enhanced in the edges

• Detection efficiency energy dependence

144 Ce source

• Blurring of the image

Further investigate the acquisition geometry and
the densitometer output
90Sr source

• Keep in mind

mm
IEEE NSS-MIC conference Rome, 18/21 October 2004
Chiara Cappellini University of Insubria-Como
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CONCLUSIONS
Thanks!!!

• 8 full size board have been assembled and
  qualified

• The possibility of relative dosimetry has been
  well assessed and proved
• Promising results have been obtained by the
  geometrical analysis with Gafchromics films
• Measurement with the pixel sensors are scheduled
  in the nearest future
• Studies on the possibility of Radiotherapic beams
  profilometry have been undertaken
• In this concern spectrometric measurements of the
  scattered radiation are also planned

Chiara Cappellini University of Insubria-Como
IEEE NSS-MIC conference Rome, 18/21 October 2004