1. DITANET Experienced Researcher
A silicon strip detector for a novel 2D dosimetric method for complex radiotherapy treatment verification
Alessio Bocci
DITANET Experienced Researcher
DITANET Workshop 08 November Alessio Bocci, CNA

2. Outline Complex radiation therapy treatments - IMRT
Detectors for dosimetric applications
RADIA2 project : experimental set-up
Measurements and results
Conclusions
DITANET Workshop 08 November Alessio Bocci, CNA

3. Motivation and Objective
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.
Objective
Characterization 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 Alessio Bocci, CNA

4. Intensity Modulated Radiation Therapy
Many beam directions and entrance points
for conformal doses distributions
modulating in space the fluence of each radiation field
Radiation therapy isa well established technique in the treatment of tumors. IMRT uses gamma-rays photons and it is a complicated tecnique
Conformal doses distributions are obtained by irradiating the patient through many beam directions and entrance points, and by modulating in space the fluence of each radiation field
DITANET Workshop 08 November Alessio Bocci, CNA

5. Dosimetry for radiotherapy verification
2D Detectors dedicated to radiotherapy
verification plans
Ionization chambers – “gold standard” detectors
Radiographic and radiochromic films
Semiconductor dosimeters: Silicon diodes
DITANET Workshop 08 November Alessio Bocci, CNA

6. Dose distribution verification
Film dosimeters: traditional detectors for verifying treatment plans dose distribution
Because Treatment Planning Systems (TPS) might miscalculate the dose delivered to the patient, dose distribution verification is essential before the irradiation of the patient
Ionization chambers and dosimetric films for planar fluence verification ara common devices for the quality assurance of the planning verification
Coronal plane
(ventral and dorsal)
Film dosimetry used as 2D dosimeters :
Advantages: high spatial resolution (sub-mm), good uniformity, axial plane
Disadvantages: Unusable as on-line detectors
and are unreliable and time consuming detectors
Axial plane
(inferior and
superior)
Sagittal plane
DITANET Workshop 08 November Alessio Bocci, CNA

7. 2D Digital Detectors in radiotherapy treatments
Single silicon detectors and ionization chambers assembled for 2D detectors
IMRTLog (ONCOlog Medical) 2D array silicon diodes
spatial resolution
0.5 to 1.0 cm
I’MRT MatriXX (Scanditronix/Wellhöfer)
array of ionizations chambers
On-line detectors
Space resolution is high, but granularity is limited by assembling difficulties.
MapCHECK (Sun Nuclear) silicon diodes
Spatial resolution is still poor with respect to film dosimeters
These 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 Alessio Bocci, CNA

8. Traditional detectors 2D commercial digital detectors
New detection systems
Traditional detectors
New detection systems
Radiographic films
Film dosimeters
2D commercial digital detectors
New detection systems
On-line no
Spatial resolution
poor
2D detectors
yes
Not monolithic!
Axial plane
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
inexpensive
radiation hard
easy to use
DITANET Workshop 08 November Alessio Bocci, CNA

9. From Nuclear Physics to Medical Applications
Medical applications can benefit from the developments on nuclear and high energy physics detector technology
Silicon strip detectors mounted
@ CNA in a telescope configuration
Silicon strip detectors Virgen Macarena Hospital in Seville
Many efforts were done to develop silicon detectors for medical physics applications, taking advantage of the experience earned in detector technology from high energy physics research (i.e., on silicon tracking detectors and data acquisition systems)
silicon tracking detectors
silicon detectors for medical
applications
DITANET Workshop 08 November Alessio Bocci, CNA

10. RADIA2 Project Si-DETECTOR
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
In this work, a feasibility study of a silicon strip detector to be used for obtaining dose maps in axial plane of a cylindrical phantom, to be applied to radiotherapy treatment verification is presented
DITANET Workshop 08 November Alessio Bocci, CNA

11. Why Silicon detectors ? Advantages:
Linear relationship between photon energy and e/h pairs ;
High sensitivity (Si eV/pair – sensitivity per unit volume: 640 nC Gy-1/mm3 )
(about 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 ;
C. Talamonti et al, NIM-A 658 (2011) 84–89
DITANET Workshop 08 November Alessio Bocci, CNA

12. Single-sided-Si-strip detectors (SSSSD)
γ photons
Radiotherapy energies
photon interactions :
Compton Effect
Secondary electrons from the phantom interacts centemeters away
Water-equivalent phantom
At therapy energies the interaction cross section of photons with the phantom material is dominated by Compton scattering, non-local contributions of secondary electrons from primary photons interacting centimeters away, contribute to the deposited dose
Signals from each strip are converted to the
absorbed dose
DITANET Workshop 08 November Alessio Bocci, CNA

13. RADIA2 Project – Collaboration
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
DITANET National Accelerator Centre (CNA)
Department of Atomic, Molecular and Nuclear Physics (FAMN),
University of Seville
3. Virgen Macarena University Hospital, Seville
4. School of Engineering, University of Seville
5. Instalaciones Inabensa S.A.
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
A. Bocci et. al., A silicon strip detector for a novel 2D dosimetric method
for radiotherapy treatment verification
submitted to NIM-a (October 2011)
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)
DITANET Workshop 08 November Alessio Bocci, CNA

14. LINAC accelerator University Hospital Virgen Macarena
(Seville, Spain)
Siemens PRIMUS linac dual energy machine operating at 6 MV photon
mode
Siemens PRIMUS linac dual energy machine operating at 6 MV photon
mode has been used to test the detection system.
A treatment planning system TPS (Philips Pinnacle) was used to calculate dose
distributions. Calculations were compared to experimental data
DITANET Workshop 08 November Alessio Bocci, CNA

15. Experimental Set-up 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 Alessio Bocci, CNA

16. Detector in the axial plane to the beam direction (axial plane)
Set-up 2:
The active area of the
detector is parallel
to the beam direction (axial plane)
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
This work is part of a more ambitious project aiming to:
Employ this prototype for obtaining D dose maps by an in-house developed algorithm dedicated to verify IMRT treatment plans.
This system is patent pending
DITANET Workshop 08 November Alessio Bocci, CNA

17. Electronics discrete electronics developed in-house
School of Engineering, University of Seville
School of Engineering, University of Seville
Charge integrators for each strip (electrometers) digitized (12 bits)
and analyzed by a Digital signal processor (DSP)
Virgen Macarena
University Hospital,
Seville
A PC allows to control and to retrieve data via an RS-232 serial bus based on a LabVIEW software
DITANET Workshop 08 November Alessio Bocci, CNA

18. Measurements Set-up 1: Linearity Detector characterization Uniformity
Calibration
Percent Depth Dose (PDD)
Penumbra
Set-up 2:
TPS and Geant4 Simulations
Angular measurements
Final calibration
Detector
characterization
Angular response
DITANET Workshop 08 November Alessio Bocci, CNA

19. Measurements Set-up 1: Linearity Detector characterization Uniformity
Calibration
Percent Depth Dose (PDD)
Penumbra
Set-up 2:
TPS and Geant4 simulations
Angular measurements
Final calibration
Detector
characterization
Angular response
DITANET Workshop 08 November Alessio Bocci, CNA

20. Linearity with dose better than 0.1 %
Set-up 1:
SSSSD perpendicular
to the beam direction
Linearity with dose better than 0.1 %
for all channels
DITANET Workshop 08 November Alessio Bocci, CNA

21. Measurements Set-up 1: Linearity Detector characterization Uniformity
Calibration
Percent Depth Dose (PDD)
Penumbra
Set-up 2:
TPS and Geant4 simulations
Angular measurements
Final calibration
Detector
characterization
Angular response
DITANET Workshop 08 November Alessio Bocci, CNA

22. Uniformity better than 0.5 %
Set-up 1:
SSSSD perpendicular
to the beam direction
Non-uniformities depend by the different strip efficiency and gain of the electronics
Uniformity better than 0.5 %
for all channels
DITANET Workshop 08 November Alessio Bocci, CNA

23. Measurements Set-up 1: Linearity Detector characterization Uniformity
Calibration
Percent Depth Dose (PDD)
Penumbra
Set-up 2:
TPS and Geant4 simulations
Angular measurements
Final calibration
Detector
characterization
Angular response
DITANET Workshop 08 November Alessio Bocci, CNA

24. Calibration Set-up 1: SSSSD perpendicular to the beam direction
Monitor Units –> Voltage -> cGy
Calibration in standard condition
radiation field 10 × 10 cm2
source-to-surface distance (SSD) = 100 cm
1.5 cm of water-equivalent solid slabs
DITANET Workshop 08 November Alessio Bocci, CNA

25. Measurements Set-up 1: Linearity Detector characterization Uniformity
Calibration
Percent Depth Dose (PDD)
Penumbra
Set-up 2:
TPS and Geant4 simulations
Angular measurements
Final calibration
Detector
characterization
Angular response
Following clinical protocols
DITANET Workshop 08 November Alessio Bocci, CNA

26. The difference between SSSSD and ionization chamber is:
Percent Depth Dose
Set-up 1:
SSSSD perpendicular
to the beam direction
Dose at different depth measured using different water-equivalent solid slabs
The difference between SSSSD and ionization chamber is:
0.68 % at 10 cm and 0.73 % at 15 cm
DITANET Workshop 08 November Alessio Bocci, CNA

27. Measurements Set-up 1: Linearity Detector characterization Uniformity
Calibration
Percent Depth Dose (PDD)
Penumbra
Set-up 2:
TPS and Geant4 simulations
Angular measurements
Final calibration
Detector
characterization
Angular response
DITANET Workshop 08 November Alessio Bocci, CNA

28. Penumbra
Region between 20 % and 80 % of the maximum dose levels at 1.5 cm water depth
SSSSD: 6.17 ± 0.56 mm - single silicon diode: 3.92 ± 0.20 mm
Set-up 1:
SSSSD perpendicular
to the beam direction
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 results
Improvements with a future prototype (next project)
DITANET Workshop 08 November Alessio Bocci, CNA

29. Measurements Set-up 1: Linearity Detector characterization Uniformity
Calibration
Percent Depth Dose (PDD)
Penumbra
Set-up 2:
Geant4 simulations and TPS calculations
Angular measurements
Final calibration
Detector
characterization
Angular response
DITANET Workshop 08 November Alessio Bocci, CNA

30. Geant4 simulations and TPS calculations
Treatment head
Geometry Model
Phantom
SSSSD Detector
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)
M. A. Cortés Giraldo, Ph. D. Thesis, 2011
DITANET Workshop 08 November Alessio Bocci, CNA

31. Measurements Set-up 1: Linearity Detector characterization Uniformity
Calibration
Percent Depth Dose (PDD)
Penumbra
Set-up 2:
Geant4 simulations and TPS calculations
Angular measurements
Final calibration
Detector
characterization
Angular response
DITANET Workshop 08 November Alessio Bocci, CNA

32. Angular response 00 Set-up 2: SSSSD parallel to the beam direction 450
Two experimental measurements
gantry
detector
3150
DITANET Workshop 08 November Alessio Bocci, CNA

33. Comparison between exp. data, TPS and Geant4
Angular Response
Steps of 450
Set-up 2:
SSSSD parallel
to the beam direction
Comparison between exp. data, TPS and Geant4
The agreement between the tendency of experimental data at different angles
and the TPS is notable
This implies that the new calibration factors are independent of the irradiation angle
Constant calibration factors
DITANET Workshop 08 November Alessio Bocci, CNA

34. Measurements Set-up 1: Linearity Detector characterization Uniformity
Calibration
Percent Depth Dose (PDD)
Penumbra
Set-up 2:
Geant4 simulations and TPS calculations
Angular measurements
Final calibration
Detector
characterization
Angular response
DITANET Workshop 08 November Alessio Bocci, CNA

35. Final Calibration Constant calibration factors Set-up 2:
SSSSD parallel
to the beam direction
Calibration factors: Experimental/TPS
gantry
detector
Calibration factors independent of
angular irradiation and of strip number
DITANET Workshop 08 November Alessio Bocci, CNA

36. Final Calibration Set-up 2: SSSSD parallel Calibrated dose
to the beam direction
Calibrated dose
gantry
detector
Relative difference between the calibrated dose and TPS calculations are better than 2 %
DITANET Workshop 08 November Alessio Bocci, CNA

37. Conclusions
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 pending
OEMP PATENT number P
DITANET Workshop 08 November Alessio Bocci, CNA

38. Future developments
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
DITANET Workshop 08 November Alessio Bocci, CNA

39. RADIA2 Project – Collaboration
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
DITANET National Accelerator Centre (CNA)
Department of Atomic, Molecular and Nuclear Physics (FAMN),
University of Seville
3. Virgen Macarena University Hospital, Seville
4. School of Engineering, University of Seville
5. Instalaciones Inabensa S.A.
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
A. Bocci et. al., A silicon strip detector for a novel 2D dosimetric method
for radiotherapy treatment verification
submitted to NIM-a (October 2011)
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)
DITANET Workshop 08 November Alessio Bocci, CNA

40. Thank you for
your
attention!!!

41. Single Strip and 2D monolithic silicon detectors
Research is directed towards silicon microstrip technology to improve spatial resolution
1. DOSI
2. CMRP DMG
128 phosphor implanted n+ strips on a p-type silicon wafer
Single crystal n-Si
128 channels
32 mm x 0.2 mm
I. Redondo-Fernandez et al,
NIM-a, (2007) 141–144
J. H. D. Wong et al.,
Medical Physics 37 (2010) 427–439
3. European project MAESTRO
Many efforts have been done to develop silicon detectors for medical applications taken the advantage of the experience earned in detector technology from nuclear and high energy physics
Pixellated monolithic silicon detectors such as the 2D array
441 Si n+p diodes
50 µm epi layer growth on MCz p.
Active area: 6.29 x 6.29 cm2.
D. Menichelli et al., Nucl. Instr. and Meth. A, 583, 109 (2007)
DITANET Workshop 08 November Alessio Bocci, CNA