DITANET Workshop 08 November 2011 Alessio Bocci, CNA 1
A silicon strip detector for a novel 2D dosimetric method for complex
radiotherapy treatment verification
Alessio BocciDITANET Experienced Researcher
Complex radiation therapy treatments - IMRTDetectors for dosimetric applications
RADIA2 project : experimental set-upMeasurements and resultsConclusions
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 2
Outline
Motivation and Objective
Motivation:Cancer is the second most frequent cause of death in developed countries. At present, although surgery is the most effective way to remove the malignant tissue, when it is combined with radiation therapy improves the cure rate by 40% approximately.
ObjectiveCharacterization of a silicon strip detector dedicated to 2D dose measurements in the axial plane of a phantom for the verification of complex radiation therapy treatment plans (i.e. IMRT)
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 3
Many beam directions and entrance points for conformal doses distributions
modulating in space the fluence of each radiation field
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 4
Intensity Modulated Radiation Therapy
Dosimetry for radiotherapy verification
Ionization chambers – “gold standard” detectors
Radiographic and radiochromic films
Semiconductor dosimeters: Silicon diodes
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 5
2D Detectors dedicated to radiotherapy verification plans
Film dosimetry used as 2D dosimeters : Advantages: high spatial resolution (sub-mm), good uniformity, axial planeDisadvantages: Unusable as on-line detectors and are unreliable and time consuming detectors
Film dosimeters: traditional detectors for verifying treatment plans dose distribution
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 6
Dose distribution verification
Axial plane(inferior and
superior)
Coronal plane(ventral and dorsal)
Sagittal plane
IMRTLog (ONCOlog Medical) 2D array silicon diodes spatial resolution
0.5 to 1.0 cm
I’MRT MatriXX (Scanditronix/Wellhöfer)array of ionizations chambers
MapCHECK (Sun Nuclear) silicon diodes
Spatial resolution is still poor with respect to film dosimetersThese devices are useful only for one irradiation angle and they can measure dose distribution
only in the coronal plane of the patient
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 7
2D Digital Detectors in radiotherapy treatments
Single silicon detectors and ionization chambers assembled for 2D detectors
New detection systemsTraditional detectors
New detection systems
It is necessary to develop new detection systems that enhance the traditional ones, and that are able to verify in a simple and accurate way complex treatment planning
Radiographic films
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 8
Film dosimeters
2D commercial digital
detectors
New detection systems
On-line no
Spatial resolution
poor
2D detectors yesNot monolithic!
Axial plane no
inexpensiveradiation hard
easy to use
Silicon strip detectors mounted @ CNA in a telescope configuration
Silicon strip detectors mounted @ Virgen Macarena Hospital in Seville
silicon tracking detectors silicon detectors for medicalapplications
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 9
From Nuclear Physics to Medical ApplicationsMedical applications can benefit from the developments on nuclear and high energy physics
detector technology
• Commercial silicon detector • Low cost
Normally used on particle detection (W1 type from Micron Semiconductor Ltd)• Single sided 16 strips (3.1 mm pitch)• Active area 50 x 50 mm² & 500 µm thick
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 10
RADIA2 Project Si-DETECTOR
Advantages:
Linear relationship between photon energy and e/h pairs ;
High sensitivity (Si - 3.6 eV/pair – sensitivity per unit volume: 640 nC Gy-1/mm3 )(about 18000 times the sensitivity per unit volume of an ionization chamber) ;
Small active volume that allows to obtain high spatial resolution ;
Well developed technology for the production of segmented monolithic planar detectors ;
Radiation hard material ;
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 11
Why Silicon detectors ?
C. Talamonti et al, NIM-A 658 (2011) 84–89
Signals from each strip are converted to the
absorbed dose
Radiotherapy energies photon interactions :
Compton Effect
Secondary electrons from the phantom interacts centemeters
away
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 12
Single-sided-Si-strip detectors (SSSSD)
Water-equivalent phantom
γ photons
Z. Abou-Haidar1, M. A. G. Alvarez1 ,R. Arrans3, A. Bocci1, M. A. Cortes-Giraldo2 , J. M. Espino2 ,M. I. Gallardo2, A. Perez Vega-Leal4
F. J. Perez Nieto5, J. M. Quesada2
1. DITANET group @ National Accelerator Centre (CNA)2. Department of Atomic, Molecular and Nuclear Physics (FAMN),
University of Seville3. Virgen Macarena University Hospital, Seville4. School of Engineering, University of Seville
5. Instalaciones Inabensa S.A.
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 13
RADIA2 Project – Collaboration
A. Bocci et. al., A silicon strip detector for a novel 2D dosimetric method for radiotherapy treatment verification
submitted to NIM-a (October 2011)
A. Bocci et. al., Empirical characterization of a silicon strip detector for a novel 2d mapped method for dosimetric verification of radiotherapy treatments, Radiotherapy and Oncology, Volume 99, Supplement 1, May 2011, Page S172
M. A. Cortes-Giraldo et al. , "Geant4 Simulation to Study the Sensitivity of a MICRON Silicon Strip Detector Irradiated by a SIEMENS PRIMUS Linac",
Progress in Nuclear Science and Technology, in press (2011)
Siemens PRIMUS linac dual energy machine operating at 6 MV photon
mode
University Hospital Virgen Macarena(Seville, Spain)
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 14
LINAC accelerator
A treatment planning system TPS (Philips Pinnacle) was used to calculate dosedistributions. Calculations were compared to experimental data
Two phantoms prototypes were designed and built Polyethylene slab material Cylindrical phantom
1. A slab phantom for:detector characterization
(sensitive area perpendicular to the beam direction)
2. A cylindrical phantom for:angular response measurements &
2D treatment plans verification in the axial plane
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 15
Experimental Set-up
Set-up 2:The active area of the
detector is parallelto the beam direction (axial plane)
This work is part of a more ambitious project aiming to:
Employ this prototype for obtaining 2D dose maps by an in-house developed algorithm dedicated to verify IMRT treatment plans.This system is patent pending
Since common ways to present dose distributions is a dose map in the patient axial plane, as an innovation the detector was placed in the cylindrical phantom in the axial plane, parallel to the beam axis
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 16
Detector in the axial plane
Charge integrators for each strip (electrometers) digitized (12 bits) and analyzed by a Digital signal processor (DSP)
discrete electronics developed in-house
A PC allows to control and to retrieve data via an RS-232 serial bus based on a LabVIEW software
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 17
Electronics
School of Engineering, University of Seville School of Engineering, University of Seville
Virgen MacarenaUniversity Hospital,
Seville
Set-up 1:• Linearity• Uniformity• Calibration• Percent Depth Dose
(PDD)• Penumbra
Set-up 2:• TPS and Geant4
Simulations• Angular measurements• Final calibration
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 18
MeasurementsDetector
characterization
Angular response
Set-up 1: Linearity • Uniformity• Calibration• Percent Depth Dose
(PDD)• Penumbra
Set-up 2:• TPS and Geant4
simulations• Angular measurements• Final calibration
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 19
MeasurementsDetector
characterization
Angular response
Linearity with dose better than 0.1 %for all channels
Set-up 1:SSSSD perpendicular to the beam direction
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 20
Linearity
Set-up 1:• Linearity Uniformity• Calibration• Percent Depth Dose
(PDD)• Penumbra
Set-up 2:• TPS and Geant4
simulations• Angular measurements• Final calibration
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 21
MeasurementsDetector
characterization
Angular response
Uniformity better than 0.5 %for all channels
Set-up 1:SSSSD perpendicular to the beam direction
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 22
Uniformity
Non-uniformities depend by the different strip efficiency and gain of the electronics
Set-up 1:• Linearity • Uniformity Calibration• Percent Depth Dose
(PDD)• Penumbra
Set-up 2:• TPS and Geant4
simulations• Angular measurements• Final calibration
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 23
MeasurementsDetector
characterization
Angular response
Calibration in standard conditionradiation field 10 × 10 cm2
source-to-surface distance (SSD) = 100 cm 1.5 cm of water-equivalent solid slabs
Set-up 1:SSSSD perpendicular to the beam direction
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 24
Calibration
Monitor Units –> Voltage -> cGy
Set-up 1:• Linearity • Uniformity• Calibration Percent Depth Dose
(PDD)• Penumbra
Set-up 2:• TPS and Geant4
simulations• Angular measurements• Final calibration
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 25
MeasurementsDetector
characterization
Angular response
The difference between SSSSD and ionization chamber is: 0.68 % at 10 cm and 0.73 % at 15 cm
Set-up 1:SSSSD perpendicular to the beam direction
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 26
Percent Depth Dose
Dose at different depth measured using different water-equivalent solid slabs
Set-up 1:• Linearity • Uniformity• Calibration• Percent Depth Dose
(PDD) Penumbra
Set-up 2:• TPS and Geant4
simulations• Angular measurements• Final calibration
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 27
MeasurementsDetector
characterization
Angular response
SSSSD penumbra value larger than the one obtained when using a single silicon detector This was mainly due to the SSSSD strips pitch of 3.1 mm
Geant4 simulations gave compatible resultsImprovements with a future prototype (next project)
Set-up 1:SSSSD perpendicular to the beam direction
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 28
Penumbra
SSSSD: 6.17 ± 0.56 mm - single silicon diode: 3.92 ± 0.20 mmRegion between 20 % and 80 % of the maximum dose levels at 1.5 cm water depth
Set-up 1:• Linearity • Uniformity• Calibration• Percent Depth Dose
(PDD)• Penumbra
Set-up 2: Geant4 simulations
and TPS calculations• Angular measurements• Final calibration
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 29
MeasurementsDetector
characterization
Angular response
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 30
Geant4 simulations and TPS calculationsTreatment headGeometry Model Phantom SSSSD Detector
M. A. Cortés Giraldo, Ph. D. Thesis, 2011
The geometry of the Siemens treatment head at 6 MV nominal energy photons, was reproduced in detail
The geometric model of the phantoms and of the SSSSD was also reproduced
The absorbed dose in each strip was calculated
Geant4 Simulations were also performed for calculating the dose-to-water case for comparisons with TPS calculations
M. A. Cortes-Giraldo et al. , "Geant4 Simulation to Study the Sensitivity of a MICRON Silicon Strip Detector Irradiated by a SIEMENS PRIMUS Linac",
Progress in Nuclear Science and Technology, in press (2011)
Set-up 1:• Linearity • Uniformity• Calibration• Percent Depth Dose
(PDD)• Penumbra
Set-up 2:• Geant4 simulations and
TPS calculations Angular measurements• Final calibration
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 31
MeasurementsDetector
characterization
Angular response
Angular response00
450
3150
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 32
gantrydetector
Set-up 2:SSSSD parallel
to the beam direction
Two experimental measurements
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 33
Angular ResponseComparison between exp.
data, TPS and Geant4
Set-up 2:SSSSD parallel
to the beam direction
Steps of 450
The agreement between the tendency of experimental data
at different anglesand the TPS is notable
This implies that the new calibration factors are
independent of the irradiation angle
Constant calibration factors
Set-up 1:• Linearity • Uniformity• Calibration• Percent Depth Dose
(PDD)• Penumbra
Set-up 2:• Geant4 simulations and
TPS calculations• Angular measurements Final calibration
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 34
MeasurementsDetector
characterization
Angular response
Calibration factors: Experimental/TPS
Calibration factors independent of angular irradiation and of strip number
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 35
Final CalibrationSet-up 2:
SSSSD parallelto the beam direction
Constant calibration factors
gantrydetector
Relative difference between the calibrated dose and TPS calculations are better than 2 %
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 36
Final Calibration
Calibrated doseSet-up 2:
SSSSD parallelto the beam direction
gantrydetector
Main Objective: Characterize and benchmark a new detection system based on a Si-strip detector dedicated to 2D dose measurements in the axial plane of a cylindrical phantom
SSSSD characterization: results shows that the prototype is suitable for IMRT verification plans (remarkable linearity, uniformity, PDD)
The angular response of the detector in the axial plane was independent of the irradiation angle and of the strip number
Geant4 simulations gave compatible results with respect to TPS and to experimental data
Final calibration with respect to TPS in the axial plane gives differences smaller than 2 % for all the strips
This system is patent pendingOEMP PATENT number P201101009
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 37
Conclusions
Future: work is in progress in order to obtain 2D dose maps from experimental data in the axial plane using an in-house developed algorithm based on the Radon Transform
A new SSSSD prototype and a new experimental set-up has been designed to improve the spatial resolution, coupling the data acquisition system with a reconstruction algorithm and with an on-line graphical interface software
Future developments
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 38
Z. Abou-Haidar1, M. A. G. Alvarez1 ,R. Arrans3, A. Bocci1, M. A. Cortes-Giraldo2 , J. M. Espino2 ,M. I. Gallardo2, A. Perez Vega-Leal4
F. J. Perez Nieto5, J. M. Quesada2
1. DITANET group @ National Accelerator Centre (CNA)2. Department of Atomic, Molecular and Nuclear Physics (FAMN),
University of Seville3. Virgen Macarena University Hospital, Seville4. School of Engineering, University of Seville
5. Instalaciones Inabensa S.A.
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 39
RADIA2 Project – Collaboration
A. Bocci et. al., A silicon strip detector for a novel 2D dosimetric method for radiotherapy treatment verification
submitted to NIM-a (October 2011)
A. Bocci et. al., Empirical characterization of a silicon strip detector for a novel 2d mapped method for dosimetric verification of radiotherapy treatments, Radiotherapy and Oncology, Volume 99, Supplement 1, May 2011, Page S172
M. A. Cortes-Giraldo et al. , "Geant4 Simulation to Study the Sensitivity of a MICRON Silicon Strip Detector Irradiated by a SIEMENS PRIMUS Linac",
Progress in Nuclear Science and Technology, in press (2011)
Thank you for your
attention!!!
Single Strip and 2D monolithic silicon detectors
Research is directed towards silicon microstrip technology to improve spatial resolution
Pixellated monolithic silicon detectors such as the 2D array
D. Menichelli et al., Nucl. Instr. and Meth. A, 583, 109 (2007)
Single crystal n-Si128 channels
32 mm x 0.2 mm
128 phosphor implanted n+ strips on a p-type silicon
waferJ. H. D. Wong et al.,
Medical Physics 37 (2010) 427–439 I. Redondo-Fernandez et al,
NIM-a, (2007) 141–144
2. CMRP DMG
441 Si n+p diodes50 µm epi layer growth on MCz p.
Active area: 6.29 x 6.29 cm2.
1. DOSI
3. European project MAESTRO
DITANET Workshop 08 November 2011 Alessio Bocci, CNA 29