The Response of ESR Dosimeters in Thermal Neutron Fields T. Schmitz 1, E. Malinen 2,3, N. Bassler 4,...

The Response ofESR Dosimeters in

Thermal Neutron Fields

T. Schmitz1, E. Malinen2,3, N. Bassler4, M. Ziegner5,6,

M. Blaickner6, H. Karle7, H. Schmidberger7,

C. Bauer8, P. Langguth9, G. Hampel1

1 Institut for Nuclear Chemistry, University of Mainz, Mainz, Germany 2 Department of Medical Physics, Oslo University Hospital, Oslo, Norway 3 Department of Physics, University of Oslo, Oslo, Norway 4 Department of Exp. Clinical Oncology, Aarhus University Hospital, Aarhus, Denmark 5 AIT Austrian Institute of Technology GmbH, Vienna, Austria 6 Institute of Atomic and Subatomic Physics, Vienna University of Technology, Vienna, Austria 7 Department of Radiooncology, University of Mainz, Mainz, Germany 8 Max Planck Institute for Polymer Research, Mainz, Germany 9 Department of Pharmacy and Toxicology, University of Mainz, Mainz, Germany

2

Outline

• Short introduction of ESR dosimetry

• Motivation and aim

• Materials and Methods

– ESR detectors: Lithium formate and Calcium carbonate

– Experimental setup at the TRIGA Mainz

• Results

– ESR readout

– Comparison measured and calculated response

– Dose components

• Summary16th International Congress on Neutron Capture Therapy, Helsinki, Finland / Tobias Schmitz, University of Mainz

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Introduction: ESR dosimetry

Alanine radicalL-α-Alanine

• The amount of radicals is measured by electron spin resonance (ESR) – spectroscopy and correlates to the absorbed dose

• Alanine is the best known ESR dosimeter

• Through ionising particles or neutrons radicals are produced in the pellets

16th International Congress on Neutron Capture Therapy, Helsinki, Finland / Tobias Schmitz, University of Mainz

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Relative Effectiveness - RE• ESR dosimeters are calibrated against

60Co-Gamma-ray source• Radical yield is particle and energy dependent

𝐷𝑑𝑒𝑡𝑒𝑐𝑡𝑜𝑟

𝑆𝑍 (𝐷¿¿𝑑𝑒𝑡𝑒𝑐𝑡𝑜𝑟 )¿𝑆𝑅𝑒𝑓 (𝑅¿¿𝑑𝑒𝑡𝑒𝑐𝑡𝑜𝑟 )=¿¿

𝑅𝑑𝑒𝑡𝑒𝑐𝑡𝑜𝑟

(Isoresponse definiton)

Z

Dose

ESR signal

D – DoseR – Response


RE calculation

• For alanine: Done with the Hansen & Olsen alanine response Model *– Based on track structure theory by Butts and Katz (again based on

Target theory)– Implemented as user-written routine to Monte Carlo code FLUKA

• For Lithium formate: Track structure theory by Butts and Katz **– Build on the assumption that dose is always deposited by

secondary electrons– Difference in detector response due to different dose distributions


N. Bassler, J.W. Hansen, H. Palmans, M.H. Holzscheiter, S. Kovacevic, and the AD-4/ACE collaboration, “The Antiproton Depth Dose Curve Measured with Alanine Detectors,” Nucl. Instrum. Meth. B 266, 929–936 (2008).*

E. Waldeland, E.O. Hole, B. Stenerlöw, E. Grusell, E. Sagstuen, and E. Malinen, “Radical Formation in Lithium Formate EPR Dosimeters after Irradiation with Protons and Nitrogen Ions,” Rad. Res. 174, 251-257 (2010)**

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Alanine results(Presented at 15th ICNCT in Tsukuba, Japan, September 2012)

0 5 10 15 20 250.0

0.4

0.8

1.2

1.6

2.0

Position according to the longitudinal axis / cm

Resp

onse

-rat

e /

Gy

min

-1

Alanine measurementFLUKA dose responseMCNP dose response


7

Motivation


Separation of dose components:• Simulation – Use of Monte Carlo Codes as FLUKA or MCNP

→ Verification – Use of different phantoms and shieldings

• Alternative – Use of different ESR materials→ Different elemental composition→ Different detector response→ Dose component identification in one irradiation combining multiple detectors

→ Can other materials be modelled as good as thealanine detector (incl. determination of RE factors)?

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ESR dosimeters

• Dosimeter materials:Calcium carbonateLithium formate

• Used as pressed pellets:Diameter: 5 mmHeight: 2.5 mm

• Irradiation in PMMA phantom10 Pellets on central length axis


• Reactor:

• Isotropic field of thermal neutrons:

Neutron flux (100 kW): 2 · 1010 n/(cm2s)

Gamma flux (100 kW): 1 · 1010 γ/(cm2s)

TRIGA Mark II Mainz – Thermal Column


Simulated build-up

FLUKA plane source

Phantom position

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ESR readout: Lithium formate

Medium line width• 60Co Photons: 1.49 mT• Neutrons: 1.58 mT

Waldeland et al; Rad Meas 46(2011)


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ESR results: Calcium carbonate

• Identical dominant radical species• No line-broadening:

→ No dose due to medium or high LET particle


0 5 10 15 200.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6


Resp

ose-

rate

/ G

y m

in-1

ESR measurementFLUKA absorbed dose

12

15 16 17 18 19 200.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8


Resp

ose-

rate

/ G

y m

in-1

Lithium formate inside boron shielding



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FLUKA results: Lithium formate


0 5 10 15 200.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0


Resp

onse

-rat

e /

Gy

min

-1



14



0 5 10 15 200.0

0.2

0.4

0.6

0.8

1.0

1.2


rela

tive

Resp

ose-

rate

Lithium formateCalcium carbonate

15



0 5 10 15 200.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0


Resp

onse

-rat

e /

Gy

min

-1

(Experimental RE = 0.42)


ESR measurementFLUKA absorbed dose Calculated RE = 0.36

t

αR

elat

ive

Flu

ence

(c

m-2

)

tα

RE factors according to

track structure theory

Particle spectra inside the detector

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Summary• Aim: Evaluation of ESR detectors for a dosimeter set

for the measurement of dose components

• Different ESR detector materials have been irradiated at the TRIGA Mainz.

• ESR readout has been compared to FLUKA calculations:– Good agreement with:

• Calcium carbonate in PMMA phantom

• Lithium formate with boron shielding

– Slight Underestimation of response:

• Lithium formate in PMMA phantom

• Theories are not limited to the alanine detector

• Both detectors are potential materials for the dosimeter set


17

Acknowledgements


http://www.wwtf.at/

Thank youfor your attention!

Cathedral in Mainz, Germany

Kiitän teitä huomiostanne!

RE calculation

• Done with the Hansen & Olsen alanine response Model*– Based on track structure theory by Butts and Katz (again based

on Target theory)– Build on the assumption that dose is always deposited by

secondary electrons– Difference in detector response due to different dose

distributions• Implemented as user-written routine to Monte Carlo code

FLUKA– Weighting of each dose deposited– Depending on type and energy of the dose depositing particle

19

Hansen, J.W. (1984). Experimental Investigation of the Suitability of the Track Structure Theory in Describing the Relative Effectiveness of High-LET Irradiation of Physical Radiation Detectors. PhD thesis, Risø National Laboratory.Hansen, J. W. and Olsen, K. J. (1984). Experimental and Calculated Response of a Radiochromiv Dye Film Dosimeter to High- LET Radiations. Radiat. Res., 91:1–15.

*


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Comparison of prim. Photon doses

1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.000.00

0.10

0.20

0.30

0.40

0.50

0.60

Pellet no.

Prim

. Pho

ton

dose

rate

/

Gy/

min

Calcium formateAmmonium formate

Lithium formate

1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.000.00

0.10

0.20

0.30

0.40

0.50

0.60

Pellet no.

Wei

ghte

d pr

im. p

hoto

n do

se

rate

/ G

y/m

in

Mass Energy Absorbtion Coefficient Ratios:

• Calcium f. / Ammonium f.:

1.36 • Calcium f. / Lithium f.:

1.33

Calculated with FLUKA:


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Primary particles in the thermal column

Neutron flux and spectrum Gamma flux and spectrum

GeVGeV


Pellet read-out

• 22

• Spectrometer: Bruker ESX

• Acquisition: 6 x 20 s with 90° rotation after 3. scan

• Analysis: Peak-to-Peak-amplitude

• Fitting functions for values below 5 Gy


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Target theory and dose distribution• Alanine dosimeters are calibrated by the NPL against

60Co-Gamma-ray source• But radical yield is particle and energy dependend

Photon irradiation Proton irradiation

Target embedded in a passive matrix

Hit: energy deposition sufficient for effect

Effect

Particle Track16th International Congress on Neutron Capture Therapy, Helsinki, Finland / Tobias Schmitz, University of Mainz

The Response of ESR Dosimeters in Thermal Neutron Fields T. Schmitz 1, E. Malinen 2,3, N. Bassler 4,...

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