A silicon microdosimeter for A silicon microdosimeter for radiation quality assessmentradiation quality assessment

(1) INFN, Sezione di Milano, via Celoria 16, 20133 Milano, Italy.(2) Politecnico di Milano, Dipartimento di Energia, Sezione di Ingegneria Nucleare CeSNEF, via Ponzio 34/3, 20133 Milano, Italy.(3) ARDENT project.

S. AGOSTEO (1,2), C.A. CASSELL(2,3), A. FAZZI (1,2),) M.V.

INTROINI (1,2), M. LORENZOLI (1,2), A. POLA (1,2), E. SAGIA(2,3), V. VAROLI (1,2).

SOLID STATE MICRODOSIMETERSSOLID STATE MICRODOSIMETERS

Si-devices can provide sensitive zones of the order of a micrometer

CHALLENGING DEVICES FOR MICRODOSIMETRY

SpectroscopyChain

Data Analysis

Silicon device

Tissue-equivalent converter

Spectrum of the energy imparted

per event in siliconMicrodosimetric

spectrum in tissue

Analytical corrections

HOW a Si-DEVICE BASED MICRODOSIMETER?…HOW a Si-DEVICE BASED MICRODOSIMETER?…

PN diodes in SOI wafer

[1] B. Rosenfeld, P. Bradley, I. Cornelius, G. Kaplan, B. Allen, J. Flanz, M. Goitein, A.V. Meerbeeck, J. Schubert, J. Bailey, Y. Tabkada, A. Maruashi, Y. Hayakawa, New silicon detector for microdosimetry applications in proton therapy, IEEE Trans. Nucl. Sci. 47(4) (2000) 1386-1394.

[2] P. Bradley, A.B. Rosenfeld, B.J. Allen, J. Coderre, and J. Capala, Performance of silicon microdosimetry detectors in boron neutron capture therapy, Radiation Research 151 (1999) 235-243.

[3] P.D. Bradley, The Development of a Novel Silicon Microdosimeter for High LET Radiation Therapy , Ph. D. Thesis, Department of Engineering Physics, University of Wollongong, Wollongong, Australia (2000).

SEGMENTED SILICON TELESCOPESEGMENTED SILICON TELESCOPE

More than 7000 pixels are connected in parallel to give an effective detection area of the ∆E stage of about 0.5 mm2

∆E stage: matrix of cylindrical diodes (h= 2 µm , d= 9 μm)

500 µm 14 µm

9 µm

E stage

Guard~2 μm

∆E element

500 µm 14 µm

9 µm

E stage

Guard~2 μm

∆E element

n+

p+p+n+

E stage ( 500 μm)

ΔE stage ( 1.9 μm)

n+

p+p+n+

E stage ( 500 μm)

ΔE stage ( 1.9 μm)

Silicon telescope: a thin ∆E stage (1.9 μm thick) coupled to a residual energy stage E (500 μm thick)on the same silicon wafer.

MICRODOSIMETRIC SPECTRA: TISSUE-MICRODOSIMETRIC SPECTRA: TISSUE-EQUIVALENCEEQUIVALENCE

AND GEOMETRICAL CORRECTIONSAND GEOMETRICAL CORRECTIONSIn order to derive microdosimetric spectra similar to those acquired by a TEPC, corrections were studied and discussed in details [1,2]

The telescope allows to optimize the tissue equivalence correction by measuring event-by-event the energy of the impinging particles and by discriminating them.

Tissue equivalence of silicon

Shape equivalence

By following a parametric criteria given in literature, the lineal energy y was calculated by considering an equivalent mean cord length.

1. S. Agosteo, P. Colautti, A. Fazzi, D. Moro and A. Pola, “A Solid State Microdosimeter based on a Monolithic Silicon Telescope”, Radiat. Prot. Dosim. 122, 382-386 (2006).

2. S. Agosteo, P.G. Fallica, A. Fazzi, M.V. Introini, A. Pola, G. Valvo, “A Pixelated Silicon Telescope for Solid State Microdosimeter”, Radiat. Meas., accepted for publication.

TISSUE EQUIVALENCE TISSUE EQUIVALENCE CORRECTIONCORRECTION

The tissue equivalence of silicon device requires:

A suitable correction to the measured distribution in order to obtain a spectrum equivalent to that acquired with an hypothetical tissue E detector

Analytical procedure for tissue-equivalence correction

Energy deposited along a track of length l by recoil-protons of energy Ep in a tissue-equivalent E detector

)E(S

)E(S)l,E(E)l,E(E

pSi

pTissue

pSidp

Tissued

Scaling factor : stopping powers ratio

TISSUE-EQUIVALENCE CORRECTIONTISSUE-EQUIVALENCE CORRECTION

The scaling factor

depends on the energy and the type of the impinging particle

)E(S

)E(SSi

Tissue

E stage of the telescope and ∆E-E scatter-plot 1 10 100 1000 10000

0.4

0.6

0.8

1.0

ST

issu

e (E)/

SS

i (E)

E (keV)

Protons Electrons

Mean value over a wide energy range (0-10 MeV) = 0.53

Electrons release only part of their energy in the E stage

Limits:the thickness of the E stage restricts the TE correction to recoil-protons below 8 MeV (alphas below 32 MeV)

SHAPESHAPE ANALYSISANALYSIS

Pixelated silicon telescope (d≈10 μm)

The correcting procedure can be based on cord length distributions, since ∆E pixels are cylinders of micrometric size in all dimensions (as the TEPCs).

Correction is only geometry-dependent (no energy limit)

0 1 2 3 4 5 60.0

0.2

0.4

0.6

0.8

1.0

1.2

p(l)

(m

-1)

l (m)

Pixelated silicon telescope Cylindrical TEPC

SHAPE ANALYSIS SHAPE ANALYSIS The equivalence of shapes is based on the parametric criteria given in the literature (Kellerer).

By assuming a constant linear energy transfer L:

By equating the dose-mean energy imparted per event for the two different shapes considered:

==

Eeq,E ll

Dimensions of ∆E stages were scaled by a factor η …

… the lineal energy y was calculated by considering an equivalent mean cord length equal to:

RESPONSE TO PROTONS:RESPONSE TO PROTONS:

Irradiations withIrradiations with62 MeV modulated proton 62 MeV modulated proton

beambeamat CATANA facilityat CATANA facility

(LNS-INFN Catania)(LNS-INFN Catania)andand

comparison with cylindrical comparison with cylindrical TEPC TEPC

(De Nardo et al., RPD 110, 1-(De Nardo et al., RPD 110, 1-4 (2004) 4 (2004)

62 MeV modulated proton beam (CATANA)62 MeV modulated proton beam (CATANA)

0 2 4 6 8 10 12 14 16 18 20 22 24 26 280.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

rel D

os

e

depth in PMMA (mm)

0 1 2 3 4 5 6 7 8 90

20

40

60

80

100

120

140

160

180

200

220

Counts per unit doseDepth = 8 mmDose = 0.3 Gy

En

erg

y d

epo

site

d i

n t

he E

sta

ge

(keV

)

Energy deposited in the E stage (MeV)

01.22.43.64.86.07.28.49.61112

0 1 2 3 4 5 6 7 8 90

20

40

60

80

100

120

140

160

180

200

220

Depth = 10.5 mmDose = 0.31 Gy

En

erg

y d

epo

site

d i

n t

he E

sta

ge

(keV

)

Energy deposited in the E stage (MeV)

Counts per unit dose

01.22.43.64.86.07.28.49.61112

0 1 2 3 4 5 6 7 8 90

20

40

60

80

100

120

140

160

180

200

220

Counts per unit doseDepth = 15.5 mmDose = 0.44 Gy

En

erg

y d

epo

site

d i

n t

he E

sta

ge

(keV

)

Energy deposited in the E stage (MeV)

01.22.43.64.86.07.28.49.61112

0 1 2 3 4 5 6 7 8 90

20

40

60

80

100

120

140

160

180

200

220Counts per unit doseDepth = 18 mm

Dose = 0.43 Gy

En

erg

y d

epo

site

d i

n t

he E

sta

ge

(keV

)

Energy deposited in the E stage (MeV)

01.22.43.64.86.07.28.49.61112

0 2 4 6 8 10 12 14 16 18 20 22 24 26 280.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

rel D

os

e

depth in PMMA (mm)

62 MeV modulated proton beam (CATANA)62 MeV modulated proton beam (CATANA)

0 1 2 3 4 5 6 7 8 90

20

40

60

80

100

120

140

160

180

200

220Counts per unit doseDepth = 20.5 mm

Dose = 0.36 Gy

En

erg

y d

epo

site

d i

n t

he E

sta

ge

(keV

)

Energy deposited in the E stage (MeV)

00.701.42.12.83.54.24.95.66.37.0

0 1 2 3 4 5 6 7 8 90

20

40

60

80

100

120

140

160

180

200

220

Counts per unit doseDepth = 21 mmDose = 0.46 Gy

En

erg

y d

epo

site

d i

n t

he E

sta

ge

(keV

)

Energy deposited in the E stage (MeV)

00.701.42.12.83.54.24.95.66.37.0

0 1 2 3 4 5 6 7 8 90

20

40

60

80

100

120

140

160

180

200

220

Counts per unit doseDepth = 21.5 mmDose = 0.62 Gy

En

erg

y d

epo

site

d i

n t

he E

sta

ge

(keV

)

Energy deposited in the E stage (MeV)

00.701.42.12.83.54.24.95.66.37.0

0 2 4 6 8 10 12 14 16 18 20 22 240.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Dep

th d

ose

curv

e (a

.u.)

depth in PMMA (mm)

0.1 1 10 100 10000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8 silicon telescope 5.7 mm cylindrical TEPC 5.7 mm (threshold) cylindrical TEPC 5.7 mm(no threshold)

y d(

y)

y (keV m-1)

0.1 1 10 100 10000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0 silicon telescope 7.6 mm cylindrical TEPC 7.6 mm

(threshold) cylindrical TEPC 7.6 mm

(no threshold)

y d(

y)

y (keV m-1)

0.1 1 10 100 10000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

silicon telescope 14.2 mm cylindrical TEPC 14.2 mm

(threshold) cylindrical TEPC 14.2 mm

(no threshold)

y d(

y)

y (keV m-1)

0.1 1 10 100 10000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0 silicon telescope 10.5 mm cylindrical TEPC 11.6 mm

(threshold) cylindrical TEPC 11.6 mm

(no threshold)

y d(

y)

y (keV m-1)

0.1 1 10 100 10000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

silicon telescope 18 mm cylindrical TEPC 18.4 mm

(threshold) cylindrical TEPC 18.4 mm

(no threshold)

y d(

y)

y (keV m-1)

Constant TE Constant TE scaling factorscaling factor

Comparison with cylindrical TEPC: Comparison with cylindrical TEPC: proximalproximal part of part of the SOBP the SOBP

0 2 4 6 8 10 12 14 16 18 20 22 240.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Dep

th d

ose

curv

e (a

.u.)

depth in PMMA (mm)

1 10 100 10000.0

0.2

0.4

0.6

0.8

1.0

silicon telescope 20.5 mm cylindrical TEPC 20.1 mm

(threshold) cylindrical TEPC 20.1 mm

(no threshold)

y d(

y)

y (keV m-1)

1 10 100 10000.0

0.2

0.4

0.6

0.8

1.0

silicon telescope 21.2 mm cylindrical TEPC 21.4 mm

(threshold) cylindrical TEPC 21.4 mm

(no threshold)

y d(

y)y (keV m-1)

1 10 100 10000.0

0.2

0.4

0.6

0.8

1.0

silicon telescope 21.4 mm cylindrical TEPC 21.6 mm

(threshold) cylindrical TEPC 21.6 mm

(no threshold)

y d(

y)

y (keV m-1)

1 10 100 10000.0

0.2

0.4

0.6

0.8

1.0

silicon telescope 21.6 mm cylindrical TEPC 21.8 mm

(threshold) cylindrical TEPC 21.8 mm

(no threshold)

y d(

y)

y (keV m-1)

1 10 100 10000.0

0.2

0.4

0.6

0.8

1.0

silicon telescope 21.8 mm cylindrical TEPC 22 mm

(threshold) cylindrical TEPC 22 mm

(no threshold)

y d(

y)

y (keV m-1)

Event-by-event Event-by-event TE correctionTE correction

Comparison with cylindrical TEPC: Comparison with cylindrical TEPC: distaldistal part of the part of the SOBP SOBP

Results:• easy-of-use system;• rapid data processing;• good measurement repeatability;• high spatial resolution;• good agreement at lineal energies higher than 7-10 keV μm-1up to the proton edge.

Problems to solve or to minimize:• high electronic noise;• counting rates, mainly related to the relative dimension between ∆E stage and E stage active areas.

Issues:• accurate estimate of dose profile;• radiation damage.

62 MeV modulated proton beam (CATANA)62 MeV modulated proton beam (CATANA)

RESPONSE TO CARBON RESPONSE TO CARBON IONS:IONS:

Irradiations withIrradiations with62 MeV/u un-modulated 62 MeV/u un-modulated carbon beam at CATANA carbon beam at CATANA

facility facility (LNS-INFN Catania)(LNS-INFN Catania)

62 MeV/u un-modulated carbon beam (CATANA)62 MeV/u un-modulated carbon beam (CATANA)

0 5 10 15 20 250.0

0.2

0.4

0.6

0.8

1.0

rela

tive

Do

se

depth in PMMA (mm)

0 20 40 60 80 100 120 140 160 1800

500

1000

1500

2000

2500

Analytical

Energy deposited in the E stage (MeV)

Ene

rgy

depo

site

d in

the E

sta

ge (

keV

) 1

2

4

7

14

27

53

103

200

Depth = 6 mm Counts

0 5 10 15 20 250.0

0.2

0.4

0.6

0.8

1.0

rela

tive

Do

se

depth in PMMA (mm)

0 20 40 60 80 100 120 140 160 1800

500

1000

1500

2000

2500

C B Be Li He H

Energy deposited in the E stage (MeV)

En

ergy

dep

osite

d in

the E

sta

ge

(keV

) 1261332751784241005

Depth = 9 mm

Counts

Analytical

62 MeV/u un-modulated carbon beam (CATANA)62 MeV/u un-modulated carbon beam (CATANA)

0 5 10 15 20 250.0

0.2

0.4

0.6

0.8

1.0

rela

tive

Do

se

depth in PMMA (mm)

0 5 10 15 20 25 30 35 40 45 500

200

400

600

800

1000

Analytical He H

Energy deposited in the E stage (MeV)

Ene

rgy

depo

site

d in

the E

sta

ge (

keV

)

1

2

4

7

14

27

53

103

200

Depth = 24 mm Counts

62 MeV/u un-modulated carbon beam (CATANA)62 MeV/u un-modulated carbon beam (CATANA)

0 1 2 3 4 5 6 7 8 9 100

2

4

6

8

10

12

14

16

18

FLUKA simulation Markus chamber silicon device

dose

(a.

u.)

depth in PMMA (mm)

Results:• high spatial resolution;• capability of operating in a complex and intense radiation field;• discrimination capability and potentialities.

Problems to solve or to minimize:• relative dimension between ∆E stage and E stage active areas;• counting rates;• radiation damage.

62 MeV/u un-modulated carbon beam (CATANA)62 MeV/u un-modulated carbon beam (CATANA)

RESPONSE TO NEUTRONS:RESPONSE TO NEUTRONS:

Irradiations withIrradiations withdifferent energy neutron different energy neutron

beambeamat CN Van de Graaff facility at CN Van de Graaff facility

(LNL-INFN Legnaro)(LNL-INFN Legnaro)

A150 plastic1 mm thick

E detector

E detector

Neutron field

Device coupled to A150 plastic:Device coupled to A150 plastic:Irradiation with monoenergetic neutronsIrradiation with monoenergetic neutrons

Irradiation with fast neutrons at different energiesIrradiation with fast neutrons at different energies

1 10 100 10000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4y

d(y)

y (keV m-1)

En= 0.7 MeV

En= 1.0 MeV

En= 1.3 MeV

En= 1.7 MeV

En= 2.7 MeV

En= 3.3 MeV

The INFN Micro-Si Experiment: study and development of a silicon microdosimeter for radiation quality assessment

Direct comparison with a cylindrical TEPC:Direct comparison with a cylindrical TEPC:y- distribution at different neutron energies Ey- distribution at different neutron energies Enn

1 10 100 10000.0

0.2

0.4

0.6

0.8

1.0

1.2 cylindrical TEPC (d=2 m) silicon telescope

y d

(y)

y (keV m-1)

1 10 100 10000.0

0.2

0.4

0.6

0.8

1.0

1.2 cylindrical TEPC (d=2 m) silicon telescope

y d

(y)

y (keV m-1)

1 10 100 10000.0

0.2

0.4

0.6

0.8

1.0

1.2 cylindrical TEPC (d=2 m) silicon telescope

y d

(y)

y (keV m-1)

1 10 100 10000.0

0.2

0.4

0.6

0.8

1.0

1.2 cylindrical TEPC (d=2 m) silicon telescope

y d

(y)

y (keV m-1)

1 10 100 10000.0

0.2

0.4

0.6

0.8

1.0

1.2 cylindrical TEPC (d=2 m) silicon telescope

y d

(y)

y (keV m-1)

1 10 100 10000.0

0.2

0.4

0.6

0.8

1.0

1.2 cylindrical TEPC (d=2 m) silicon telescope

y d

(y)

y (keV m-1)

En= 0.64 MeV En= 0.96 MeV En= 1.27 MeV

En= 2.3 MeVEn= 1.89 MeVEn= 1.58 MeV

0.0 0.5 1.0 1.5 2.0 2.5 3.030

40

50

60

70

80

90

Silicon Telescope Cylindrical TEPC (d = 2 m)

y D (

keV

m

-1)

Neutron energy (MeV)

Uncertainties:Si Telescope 8% -11%TEPC: 4% - 7%

Direct comparison with a cylindrical TEPC:Direct comparison with a cylindrical TEPC:y- distribution at different neutron energies Ey- distribution at different neutron energies Enn

Results:• easy-of-use system;• good measurement repeatability;• good agreement at lineal energies higher than 7-10 keV μm-1up to the proton edge.

Problems to solve or to minimize:• high electronic noise;• thick detector dead layer.

Issues:• poly-energetic neutron fields;• angular response;• contribution of electrons to microdosimetric spectra (low y- values).

Irradiation with fast neutrons at different energiesIrradiation with fast neutrons at different energies

CONCLUSIONSCONCLUSIONS

IMPROVEMENT OF THE IMPROVEMENT OF THE ENERGY TRESHOLD:ENERGY TRESHOLD:

A feasibility study of a low-A feasibility study of a low-LET silicon microdosimeterLET silicon microdosimeter

Improvement of the energy thresholdImprovement of the energy threshold

The main limitation of the system is the high energy threshold imposed by the electronic noise.

A feasibility study with a low-noise set-up based on discrete components was carried out in order to test this assertion

New design of the segmented telescope with a ∆E stage having a lower number of cylinders connected in parallel and an E stage with an optimized sensitive area

1. Decrease the energy threshold below 1 keV μm-1

2. Optimize the counting rate of the two stages

Improvement of the energy threshold: Improvement of the energy threshold: Test with a Cesium-137 sourceTest with a Cesium-137 source

A telescope constituted by a single ΔE cylinder coupled to an E stage was irradiated with β particles emitted by a 137Cs source

0.01 0.1 1 10 1000.0

0.2

0.4

0.6

0.8

1.0 Monopixel

y d(

y)

y (keV m-1)

0.01 0.1 1 10 1000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

FLUKA simulation (tissue) Experimental

y d(

y)

y (keV m-1)

Improvement of the energy threshold:Improvement of the energy threshold:Test of the tissue-equivalence correction Test of the tissue-equivalence correction

procedure for electronsprocedure for electrons

Lineal energy threshold ≈ 0.6 keV μm-1

Improvement of the energy threshold:Improvement of the energy threshold:Irradiation with 2.3 MeV neutrons at LNL CN Irradiation with 2.3 MeV neutrons at LNL CN

facilityfacility