- Email: [email protected]
Silicon Ultra fast Cameras for electron and γ sources In Medical Applications: a progress report
Nuclear Physics B (Proc. Suppl.) 150 (2006) 308–312 www.elsevierphysics.com
Silicon Ultra fast Cameras for electron and γ sources In Medical Applications: a progress report∗ A. Bulgheronia † , L. Badanob , D. Berstc , C. Bianchid , J. Bole , M. Cacciaa , C. Cappellinia , G. Clausc , C. Colledanic , L. Conted , A. Czermakf , G. Deptuchc , W. de Boere , K. Domanskig , W. Dulinskic , B. Dulnyf , O. Ferrandob, E. Grigorievh‡ , P. Grabiecg , M. Grodnerg , R. Lorussod, B. Jaroszewiczg, M. Jastrzabi L. Jungermanne , T. Klatkai , A. Kociubinskig , M. Kozieli, W. Kucewiczi , K. Kucharskig , S. Kutai , J. Marczewskig , A. Mozzanicaa, H. Niemeci , R. Novariod, L. Paoluccia, Y. Popowskih, M. Prest, oa , A. Przykuttaj, J-L Riesterc , M. Roverea, M. Sapori , H. Schweickertk, B. Sowickif , B. Span` i g f M. Szelezniak , D. Tomaszewski , A. Zalewska a
Universit` a dell’Insubria, Dipartimento di Fisica e Matematica – Como (Italy) b
Fondazione per Adroterapia Oncologica – Novara (Italy)
c Universit´e Luis Pasteur, Laboratoire d’Electronique et de Physique des Syst`emes Instrumentaux – Strasbourg (France) Centre National de la Recherce Scientifique / IN2P3 – Paris (France) d
Universit` a dell’Insubria, Dipartimento di Scienze Cliniche e Biologiche – Varese (Italy)
e
Universitaet Karlsruhe, Institut fuer Experimentelle Kernphysik – Karlsruhe (Germany) f
H. Niewodniczanski Insitute of Nuclear Physics – Krakow (Poland)
g
Institute of Electron Technology – Warsaw (Poland)
h
Universit´e de Gen`eve, Gen`eve (Switzerland)
i
AGH - University of Science and Technology Electronics Department, – Krakow (Poland), j
Eurotope Entwicklungsgesellschaft fuer isotopentechnologien – Berlin (Germany)
k
ZAG-Zyklotron AG – Karlsruhe (Germany)
SUCIMA (Silicon Ultra fast Cameras for electron and γ sources In Medical Applications) is a project approved by the European Commission within the Fifth Framework Programme, with the primary goal of developing a real time dosimeter based on direct detection of ionising particles in a position sensitive Silicon sensor. The main applications of this device are imaging of intravascular brachytherapy radioactive sources with activities up to 3 GBq and real time monitoring of hadrontherapy beams. In order to perform a feasibility study, during the first two years a real time dosimeter has been engineered using Silicon microstrip detectors read out by an integrating dead-timeless front-end electronics. The prototypes have been qualified as relative dosimeter with respect to certified secondary standards; moreover, further measurements are on going in order to investigate the possibility to use the sensors as absolute dosimeters. Since the final device is supposed to provide a two dimensional image, two different Monolithic Active Pixel dosimeters have been designed and produced by the collaboration based on CMOS and Silicon On Insulator technologies. The main features of the two sensors are presented in this paper. 0920-5632/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2004.08.044
A. Bulgheroni et al. / Nuclear Physics B (Proc. Suppl.) 150 (2006) 308–312
1. Introduction SUCIMA (Silicon Ultrafast Cameras for electrons and γ sources In Medical Applications) is an European Commission Project, within the Fifth Framework programme, started in November 2001 and with a three year duration. The main goal of the SUCIMA project is the development of an advanced imaging technique of extended radioactive sources used in medical applications, where imaging has to be intended as the record of a dose map [1]. The two main medical applications foreseen by the Collaboration are: intravascular brachytherapy and beam monitoring of proton and light ion beams used in radiotherapy, briefly described in the following. 1.1. Intravascular brachyteraphy Coronary artery diseases are the leading cause of morbidity and mortality in the western world. Re-establishing a stable and normal artery cross section (lumen) is the primary goal of angioplasty. Re-narrowing of the artery (restenosis) is the major limitation of angioplasty. Clinical studies indicate that intra-arterial irradiation reduces substantially the problem of restenosis [2]. Local radiotherapy (named intravascular brachytherapy) is performed on a few centimeter long section of the vessel and it is usually accomplished by multiple point-like radioactive sources. During the radiation treatment the patient will have significantly reduced arterial blood flow, therefore, in order to reduce risks of complications, doses in excess of 5 Gy/min are achieved with a total delivered dose between 8 to 30 Gy. These high dose rates are accomplished by β emitting source with activities in the GBq range. 1.2. Hadrontherapy beam monitor Radiotherapic treatments based on X-rays are currently envisaged for 50% of patients affected by tumours. Among these, 30-40% (i.e. 25 000 patients per year in Europe) are diagnosed as having a tumour or lesions that could benefit from irradiation with light ion beams and no better ∗ Authors’
research is supported by the European Commission under the contract G1RD-CT-2001-00561 † Corresponding author; [email protected] ‡ on leave of absence from ITEP, Moscow, Russia
309
alternative exists for a sub-set corresponding to 10% of them [3]. The beam diagnostic system of a hospital based light ion accelerator for tumour radiotherapy is crucial as it determines an efficient and safe operation of the beam lines. The real time beam monitor proposed by the collaboration is based on the detection of secondary electrons emerging from a thin foil crossed by the beam. The beam size, position and intensity are determined focusing the secondary electrons accelerated up to 20 keV onto a position and energy sensitive detector [4]. 2. Detector R&D The key feature of the proposed detector is the reconstruction of the spatial distribution of energy deposited by a continuos flow of particles springing off an extended source. The applications described above are determing the boundary conditions for the detector R&D (listed in Table 1 and in [1]). As far as radiation tolerance is concerned, it is worth mentioning that the major constraints are expected by imaging brachytherapy sources; in fact secondary electrons from the target in the beam monitor will have a maximum kinetic energy of 20 keV, corresponding to 3 μm range in Si, and will be absorbed in the sensitive volume of the sensor without affecting the front end circuit. On the other hand, the requirement of sensitivity to low energy particles is heavily constraining the sensor technology, since any dead layer has to be avoided. The major goal of the project is the development of a monolithic pixel detector in CMOS and SOI technology fullfilling those requirements; in order to provide an early feedback by the end-users, a hybrid detector based on the Silicon micro-strips sensors from the AGILE experiment has been engineered and used in a feasibility study [5]. 2.1. CMOS sensors The use of specialized CMOS imagers (from the MIMOSA’s family) for charged particle detection has been recently demonstrated, with emphasis on readout speed and on resolution at the micron level for particle tracking in high energy physics applications [6]. The SUCIMA
310
A. Bulgheroni et al. / Nuclear Physics B (Proc. Suppl.) 150 (2006) 308–312
Table 1 Specific requirements on the detector by brachytherapy and real time beam monitor applications. A demagnification factor 5 has been assumed for real time beam imaging. Requirement Real time monitor Brachytherapy 2 Sensitive Area 15 × 15 mm 70 × 30 mm2 Granularity ≈ 0.200 mm ≈ 0.050 mm Read-out speed 10 000 frames/s no special request Dynamic range 0.2 - 2000 m.i.p./pixel/100μs 1 m.i.p./pixel/100μs Radiation tolerance 5 - 5000 rad/s 2 - 22 rad/s 55
Fe spectrum before and after irradiation
Entries
development focuses on radiation hardness and on backthinning, with the aim to enhance the sensitivity to low energy particles.
600 Lengend Before irradiation After 500 krad After 1 Mrad
500
400
2.1.1. Radiation hardness A preliminary study of radiation tolerance of a CMOS particle sensor [7] has shown a significant charge collection inefficiency after a few hundreds krad dose by ionising radiation. Further investigations lead to the hypothesis that the charge losses may be explained by the existence of a competitive collection path through the P-well embedding the electronics, partially depleted by the bias voltage of the reset transistor. In order to overcome this problem, a specific layout has been developed where the readout electronics of four pixels is insulated using a circular N-well guard ring and four L-shaped sensing N-well diodes surrond the periphery. The first SUCIMA prototype, named SUCCESSOR1 (SUCIMA CMOS ChargE SenSOR), has been sumitted in AMIS 0.35 μm technology implementing several different layouts. Preliminary irradiation tests have proven the tolerance at least up to 1 Mrad (Figure 1) and are being continued on a larger sample of chips and to higher doses. 2.1.2. Backthinning An intense program on backthinning of the Silicon bulk down to the epitaxial layer is currently ongoing on the final large scale prototype designed for the beam monitor application, while a preliminary technological test has been done on 8 wafers with 30 MIMOSA 5 sensors each. Chip characterization tests are still on going but, as of
300
200
100
0 0
50
100
150
200
250
300
350
400 450 ADC counts
55
Figure 1. Fe spectra for a 3 × 3 pixels cluster before irradiation, after 500 krad and after 1 Mrad.
today, neither a reduction in the overall yield has been observed nor a change in the sensor figure of merit. To prove the sensitivity to short range particles a counting experiment with α particles 241 Am source has been set up. The practifrom cal range of α particles in Silicon (Figure 2) can be tuned changing the kinetic energy of the impinging particles simply varying the distance in air between the source and the sensor. A Monte Carlo simulation has been perfomed to estimate the α range, the straggling and the energy spectra at different source detector distances. The geometry of the source and detector system and the random generation of the α particle direction have been coded in a dedicated program while the ion transport and energy loss
311
A. Bulgheroni et al. / Nuclear Physics B (Proc. Suppl.) 150 (2006) 308–312 Number of detected particles (normalized)
Range [um]
Alpha particle range in Si vs air thickness 25
1
20
0.8
15
0.6
10
0.4
5
0.2
Legend Extended source in air Experimental data
0 0
0.5
1
1.5
2
2.5
3
3.5 4 Air gap [cm]
Figure 2. α particle range as a function of the source–detector distance in air. At 3 cm the energy spectrum of the impinging particles is centered around 1.9 M eV with an r.m.s. of 100 keV , while the range straggling is at the 7% level.
was based on SRIM1 . Simulation and experimental results are plotted in Figure 3 where no loss in the counting rate beyond the pure geometrical effect is observed. This preliminary experiment is proving that the sensor is able to detect particles having a pratical range in Silicon of only a few microns. Extensive tests proving the sensitivity to low energy e− are on going with a hybrid photodiode setup. 2.1.3. Larger scale submissions Two full scale prototypes have been finalized. The sensors customized for the beam monitor features a sensitive area of 17 × 19 mm2 ; it has been submitted in AMS 0.6 μm technology and the delivery is expected by the end of July 2004. The sensor for brachytherapy source dosimetry with the improved radiation tolerance and a sensitive area of 7.7 × 8.2 mm2 is being submitted in AMIS 0.35 μm. 2.2. SOI sensors Silicon On Insulator technology offers the possibility of engineering a monolithic device with a fully depleted sensitive volume. This novel sensor relies on the integration of the Front End elec1 This
software is available at http://www.srim.org
0 0
0.5
1
1.5
2
2.5 3 3.5 4 Source detector distance [cm]
Figure 3. Number of detected α particles versus the source–detector distance. The number of entries has been normalized to the number obtained at the smallest distance (0.2 cm).
tronics in the device layer of a SOI wafer with a high resistive substrate. The fundamental principles and the technological sequence have been described elsewhere ([9]). In order to validate the concept, a special test vehicle including 8 × 8 pixels matrices was designed and fabricated. 2.2.1. Functionality assessment Sensitivity to ionising radiation. The sensor sensitivity to ionising radiation has been 90 tested using a β emitter ( Sr). The typical Landau shape of the cluster pulse height is compared to the distribution of the output voltage once the pedestal has been subtracted (Figure 4). Sensitivity to short range particles. Since the SOI option allows the use of a fully depleted sensor, no problems with short range particles detection are expected, once the particle range is greater than the non sensitive layer and the ohmic contact region. This dead layer can be easily reduced below 1μm. A test with an α emitter proved the sensitivity to short range particles [10]. Dynamic range. According to the specifications (Table 1) the detector has been designed to have a very high dynamic range.
312
A. Bulgheroni et al. / Nuclear Physics B (Proc. Suppl.) 150 (2006) 308–312 90
Entries
Sr Signal Legend Output voltage Gaussian fit MIP signal Landau fit
100
80
60
40
20
0 -40
REFERENCES -20
0
20
40
60
80
100
120
140 160 180 ADC counts
Figure 4. The Landau shape of cluster pulse height created by a MIP is compared to the output voltage distribution after pedestal subtracted.
A fairly good linearity up to 80 minimum ionizining particles has been measured in [10] both by increasing the charge injected from an external voltage generator to a readout channel and by increasing the number of infrared laser pulses shining directly on the backplane of the test matrices. 2.2.2. Large scale prototype A new large scale prototype with 128 × 128 pixels 150μm pitch and a sensitive area of 19.6 × 19.6 mm2 has been submitted for production at the Institute of Electron Technology in Warsaw. The design of this sensor is such that two sensors can be stitched with a very narrow dead area in between, doubling the overall sensitive area. Moreover an adapter board with a multiplexed connection to the DAQ2 and a mosaic of several sensors is in production. 3. Conclusion The SUCIMA collaboration involves Medical Doctors, Physicists, Engineers and industrial partners, which provide the synergy to achieve the ambitious goals of the project, namely fast 2 The
real time monitoring of a hadron beam in radiotherapy treatments and dosimetry of extended radioactive sources. After thirty months since the beginning, the project can be considered on schedule and all of the milestones in the workplane, assumed to be completed by the end of 2004, have been achieved.
DAQ has also been developed within the collaboration. It is described in detail in [11].
1. M. Caccia et al., Nuclear Physics B (Proc. Suppl.) 125 (2003) 133-138 2. V. Verin et al., New Engl. Jou. Med. 344 (2001) 243 3. U. Amaldi and B. Larsson (eds), Hadrontheraphy in oncology, Proceedings of the First International Symposium on Hadrontherapy, Como, Italy, 18–21 October 1993; Excerpta Medica, Elsevier International Congress Series 1077 4. L. Badano et al., Proceedings of the 6th European Workshop on Beam Diagnostic and Instrumentation for Particle Accelerators, DIPAC - Mainz 2003, pp. 77-79. 5. C. Cappellini et al., Nuclear Inst. and Methods in Physics Research, A 527 (2004) 46 – 49 6. G. Deptuch et al., IEEE Trans. Nucl. Sci. 49 (2002) 601 7. M. Deveaux et al., Nuclear Inst. and Methods in Physics Research, A 512 (2003) 71 – 76 8. J. F. Ziegler, J. P. Biersack, U. Littmark, The Stopping and Range of Ions is Solids Pergamon Press, New York (2003) 9. M. Amati et al., Nuclear Inst. and Methods in Physics Research, A 511 (2003) 265 – 270 ˙ 10. J.Marczewski et al., IEEE Trans. on Nucl. Sci. Volume 51, Issue 3, Pages 10124 – 1028 11. A. Czermak et al., Proceedings of the 8th ICATPP - Como (2003)
Silicon Ultra fast Cameras for electron and γ sources In Medical Applications: a progress report∗ A. Bulgheronia † , L. Badanob , D. Berstc , C. Bianchid , J. Bole , M. Cacciaa , C. Cappellinia , G. Clausc , C. Colledanic , L. Conted , A. Czermakf , G. Deptuchc , W. de Boere , K. Domanskig , W. Dulinskic , B. Dulnyf , O. Ferrandob, E. Grigorievh‡ , P. Grabiecg , M. Grodnerg , R. Lorussod, B. Jaroszewiczg, M. Jastrzabi L. Jungermanne , T. Klatkai , A. Kociubinskig , M. Kozieli, W. Kucewiczi , K. Kucharskig , S. Kutai , J. Marczewskig , A. Mozzanicaa, H. Niemeci , R. Novariod, L. Paoluccia, Y. Popowskih, M. Prest, oa , A. Przykuttaj, J-L Riesterc , M. Roverea, M. Sapori , H. Schweickertk, B. Sowickif , B. Span` i g f M. Szelezniak , D. Tomaszewski , A. Zalewska a
Universit` a dell’Insubria, Dipartimento di Fisica e Matematica – Como (Italy) b
Fondazione per Adroterapia Oncologica – Novara (Italy)
c Universit´e Luis Pasteur, Laboratoire d’Electronique et de Physique des Syst`emes Instrumentaux – Strasbourg (France) Centre National de la Recherce Scientifique / IN2P3 – Paris (France) d
Universit` a dell’Insubria, Dipartimento di Scienze Cliniche e Biologiche – Varese (Italy)
e
Universitaet Karlsruhe, Institut fuer Experimentelle Kernphysik – Karlsruhe (Germany) f
H. Niewodniczanski Insitute of Nuclear Physics – Krakow (Poland)
g
Institute of Electron Technology – Warsaw (Poland)
h
Universit´e de Gen`eve, Gen`eve (Switzerland)
i
AGH - University of Science and Technology Electronics Department, – Krakow (Poland), j
Eurotope Entwicklungsgesellschaft fuer isotopentechnologien – Berlin (Germany)
k
ZAG-Zyklotron AG – Karlsruhe (Germany)
SUCIMA (Silicon Ultra fast Cameras for electron and γ sources In Medical Applications) is a project approved by the European Commission within the Fifth Framework Programme, with the primary goal of developing a real time dosimeter based on direct detection of ionising particles in a position sensitive Silicon sensor. The main applications of this device are imaging of intravascular brachytherapy radioactive sources with activities up to 3 GBq and real time monitoring of hadrontherapy beams. In order to perform a feasibility study, during the first two years a real time dosimeter has been engineered using Silicon microstrip detectors read out by an integrating dead-timeless front-end electronics. The prototypes have been qualified as relative dosimeter with respect to certified secondary standards; moreover, further measurements are on going in order to investigate the possibility to use the sensors as absolute dosimeters. Since the final device is supposed to provide a two dimensional image, two different Monolithic Active Pixel dosimeters have been designed and produced by the collaboration based on CMOS and Silicon On Insulator technologies. The main features of the two sensors are presented in this paper. 0920-5632/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2004.08.044
A. Bulgheroni et al. / Nuclear Physics B (Proc. Suppl.) 150 (2006) 308–312
1. Introduction SUCIMA (Silicon Ultrafast Cameras for electrons and γ sources In Medical Applications) is an European Commission Project, within the Fifth Framework programme, started in November 2001 and with a three year duration. The main goal of the SUCIMA project is the development of an advanced imaging technique of extended radioactive sources used in medical applications, where imaging has to be intended as the record of a dose map [1]. The two main medical applications foreseen by the Collaboration are: intravascular brachytherapy and beam monitoring of proton and light ion beams used in radiotherapy, briefly described in the following. 1.1. Intravascular brachyteraphy Coronary artery diseases are the leading cause of morbidity and mortality in the western world. Re-establishing a stable and normal artery cross section (lumen) is the primary goal of angioplasty. Re-narrowing of the artery (restenosis) is the major limitation of angioplasty. Clinical studies indicate that intra-arterial irradiation reduces substantially the problem of restenosis [2]. Local radiotherapy (named intravascular brachytherapy) is performed on a few centimeter long section of the vessel and it is usually accomplished by multiple point-like radioactive sources. During the radiation treatment the patient will have significantly reduced arterial blood flow, therefore, in order to reduce risks of complications, doses in excess of 5 Gy/min are achieved with a total delivered dose between 8 to 30 Gy. These high dose rates are accomplished by β emitting source with activities in the GBq range. 1.2. Hadrontherapy beam monitor Radiotherapic treatments based on X-rays are currently envisaged for 50% of patients affected by tumours. Among these, 30-40% (i.e. 25 000 patients per year in Europe) are diagnosed as having a tumour or lesions that could benefit from irradiation with light ion beams and no better ∗ Authors’
research is supported by the European Commission under the contract G1RD-CT-2001-00561 † Corresponding author; [email protected] ‡ on leave of absence from ITEP, Moscow, Russia
309
alternative exists for a sub-set corresponding to 10% of them [3]. The beam diagnostic system of a hospital based light ion accelerator for tumour radiotherapy is crucial as it determines an efficient and safe operation of the beam lines. The real time beam monitor proposed by the collaboration is based on the detection of secondary electrons emerging from a thin foil crossed by the beam. The beam size, position and intensity are determined focusing the secondary electrons accelerated up to 20 keV onto a position and energy sensitive detector [4]. 2. Detector R&D The key feature of the proposed detector is the reconstruction of the spatial distribution of energy deposited by a continuos flow of particles springing off an extended source. The applications described above are determing the boundary conditions for the detector R&D (listed in Table 1 and in [1]). As far as radiation tolerance is concerned, it is worth mentioning that the major constraints are expected by imaging brachytherapy sources; in fact secondary electrons from the target in the beam monitor will have a maximum kinetic energy of 20 keV, corresponding to 3 μm range in Si, and will be absorbed in the sensitive volume of the sensor without affecting the front end circuit. On the other hand, the requirement of sensitivity to low energy particles is heavily constraining the sensor technology, since any dead layer has to be avoided. The major goal of the project is the development of a monolithic pixel detector in CMOS and SOI technology fullfilling those requirements; in order to provide an early feedback by the end-users, a hybrid detector based on the Silicon micro-strips sensors from the AGILE experiment has been engineered and used in a feasibility study [5]. 2.1. CMOS sensors The use of specialized CMOS imagers (from the MIMOSA’s family) for charged particle detection has been recently demonstrated, with emphasis on readout speed and on resolution at the micron level for particle tracking in high energy physics applications [6]. The SUCIMA
310
A. Bulgheroni et al. / Nuclear Physics B (Proc. Suppl.) 150 (2006) 308–312
Table 1 Specific requirements on the detector by brachytherapy and real time beam monitor applications. A demagnification factor 5 has been assumed for real time beam imaging. Requirement Real time monitor Brachytherapy 2 Sensitive Area 15 × 15 mm 70 × 30 mm2 Granularity ≈ 0.200 mm ≈ 0.050 mm Read-out speed 10 000 frames/s no special request Dynamic range 0.2 - 2000 m.i.p./pixel/100μs 1 m.i.p./pixel/100μs Radiation tolerance 5 - 5000 rad/s 2 - 22 rad/s 55
Fe spectrum before and after irradiation
Entries
development focuses on radiation hardness and on backthinning, with the aim to enhance the sensitivity to low energy particles.
600 Lengend Before irradiation After 500 krad After 1 Mrad
500
400
2.1.1. Radiation hardness A preliminary study of radiation tolerance of a CMOS particle sensor [7] has shown a significant charge collection inefficiency after a few hundreds krad dose by ionising radiation. Further investigations lead to the hypothesis that the charge losses may be explained by the existence of a competitive collection path through the P-well embedding the electronics, partially depleted by the bias voltage of the reset transistor. In order to overcome this problem, a specific layout has been developed where the readout electronics of four pixels is insulated using a circular N-well guard ring and four L-shaped sensing N-well diodes surrond the periphery. The first SUCIMA prototype, named SUCCESSOR1 (SUCIMA CMOS ChargE SenSOR), has been sumitted in AMIS 0.35 μm technology implementing several different layouts. Preliminary irradiation tests have proven the tolerance at least up to 1 Mrad (Figure 1) and are being continued on a larger sample of chips and to higher doses. 2.1.2. Backthinning An intense program on backthinning of the Silicon bulk down to the epitaxial layer is currently ongoing on the final large scale prototype designed for the beam monitor application, while a preliminary technological test has been done on 8 wafers with 30 MIMOSA 5 sensors each. Chip characterization tests are still on going but, as of
300
200
100
0 0
50
100
150
200
250
300
350
400 450 ADC counts
55
Figure 1. Fe spectra for a 3 × 3 pixels cluster before irradiation, after 500 krad and after 1 Mrad.
today, neither a reduction in the overall yield has been observed nor a change in the sensor figure of merit. To prove the sensitivity to short range particles a counting experiment with α particles 241 Am source has been set up. The practifrom cal range of α particles in Silicon (Figure 2) can be tuned changing the kinetic energy of the impinging particles simply varying the distance in air between the source and the sensor. A Monte Carlo simulation has been perfomed to estimate the α range, the straggling and the energy spectra at different source detector distances. The geometry of the source and detector system and the random generation of the α particle direction have been coded in a dedicated program while the ion transport and energy loss
311
A. Bulgheroni et al. / Nuclear Physics B (Proc. Suppl.) 150 (2006) 308–312 Number of detected particles (normalized)
Range [um]
Alpha particle range in Si vs air thickness 25
1
20
0.8
15
0.6
10
0.4
5
0.2
Legend Extended source in air Experimental data
0 0
0.5
1
1.5
2
2.5
3
3.5 4 Air gap [cm]
Figure 2. α particle range as a function of the source–detector distance in air. At 3 cm the energy spectrum of the impinging particles is centered around 1.9 M eV with an r.m.s. of 100 keV , while the range straggling is at the 7% level.
was based on SRIM1 . Simulation and experimental results are plotted in Figure 3 where no loss in the counting rate beyond the pure geometrical effect is observed. This preliminary experiment is proving that the sensor is able to detect particles having a pratical range in Silicon of only a few microns. Extensive tests proving the sensitivity to low energy e− are on going with a hybrid photodiode setup. 2.1.3. Larger scale submissions Two full scale prototypes have been finalized. The sensors customized for the beam monitor features a sensitive area of 17 × 19 mm2 ; it has been submitted in AMS 0.6 μm technology and the delivery is expected by the end of July 2004. The sensor for brachytherapy source dosimetry with the improved radiation tolerance and a sensitive area of 7.7 × 8.2 mm2 is being submitted in AMIS 0.35 μm. 2.2. SOI sensors Silicon On Insulator technology offers the possibility of engineering a monolithic device with a fully depleted sensitive volume. This novel sensor relies on the integration of the Front End elec1 This
software is available at http://www.srim.org
0 0
0.5
1
1.5
2
2.5 3 3.5 4 Source detector distance [cm]
Figure 3. Number of detected α particles versus the source–detector distance. The number of entries has been normalized to the number obtained at the smallest distance (0.2 cm).
tronics in the device layer of a SOI wafer with a high resistive substrate. The fundamental principles and the technological sequence have been described elsewhere ([9]). In order to validate the concept, a special test vehicle including 8 × 8 pixels matrices was designed and fabricated. 2.2.1. Functionality assessment Sensitivity to ionising radiation. The sensor sensitivity to ionising radiation has been 90 tested using a β emitter ( Sr). The typical Landau shape of the cluster pulse height is compared to the distribution of the output voltage once the pedestal has been subtracted (Figure 4). Sensitivity to short range particles. Since the SOI option allows the use of a fully depleted sensor, no problems with short range particles detection are expected, once the particle range is greater than the non sensitive layer and the ohmic contact region. This dead layer can be easily reduced below 1μm. A test with an α emitter proved the sensitivity to short range particles [10]. Dynamic range. According to the specifications (Table 1) the detector has been designed to have a very high dynamic range.
312
A. Bulgheroni et al. / Nuclear Physics B (Proc. Suppl.) 150 (2006) 308–312 90
Entries
Sr Signal Legend Output voltage Gaussian fit MIP signal Landau fit
100
80
60
40
20
0 -40
REFERENCES -20
0
20
40
60
80
100
120
140 160 180 ADC counts
Figure 4. The Landau shape of cluster pulse height created by a MIP is compared to the output voltage distribution after pedestal subtracted.
A fairly good linearity up to 80 minimum ionizining particles has been measured in [10] both by increasing the charge injected from an external voltage generator to a readout channel and by increasing the number of infrared laser pulses shining directly on the backplane of the test matrices. 2.2.2. Large scale prototype A new large scale prototype with 128 × 128 pixels 150μm pitch and a sensitive area of 19.6 × 19.6 mm2 has been submitted for production at the Institute of Electron Technology in Warsaw. The design of this sensor is such that two sensors can be stitched with a very narrow dead area in between, doubling the overall sensitive area. Moreover an adapter board with a multiplexed connection to the DAQ2 and a mosaic of several sensors is in production. 3. Conclusion The SUCIMA collaboration involves Medical Doctors, Physicists, Engineers and industrial partners, which provide the synergy to achieve the ambitious goals of the project, namely fast 2 The
real time monitoring of a hadron beam in radiotherapy treatments and dosimetry of extended radioactive sources. After thirty months since the beginning, the project can be considered on schedule and all of the milestones in the workplane, assumed to be completed by the end of 2004, have been achieved.
DAQ has also been developed within the collaboration. It is described in detail in [11].
1. M. Caccia et al., Nuclear Physics B (Proc. Suppl.) 125 (2003) 133-138 2. V. Verin et al., New Engl. Jou. Med. 344 (2001) 243 3. U. Amaldi and B. Larsson (eds), Hadrontheraphy in oncology, Proceedings of the First International Symposium on Hadrontherapy, Como, Italy, 18–21 October 1993; Excerpta Medica, Elsevier International Congress Series 1077 4. L. Badano et al., Proceedings of the 6th European Workshop on Beam Diagnostic and Instrumentation for Particle Accelerators, DIPAC - Mainz 2003, pp. 77-79. 5. C. Cappellini et al., Nuclear Inst. and Methods in Physics Research, A 527 (2004) 46 – 49 6. G. Deptuch et al., IEEE Trans. Nucl. Sci. 49 (2002) 601 7. M. Deveaux et al., Nuclear Inst. and Methods in Physics Research, A 512 (2003) 71 – 76 8. J. F. Ziegler, J. P. Biersack, U. Littmark, The Stopping and Range of Ions is Solids Pergamon Press, New York (2003) 9. M. Amati et al., Nuclear Inst. and Methods in Physics Research, A 511 (2003) 265 – 270 ˙ 10. J.Marczewski et al., IEEE Trans. on Nucl. Sci. Volume 51, Issue 3, Pages 10124 – 1028 11. A. Czermak et al., Proceedings of the 8th ICATPP - Como (2003)