1. The Response of ESR 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
Summary
16th International Congress on Neutron Capture Therapy, Helsinki, Finland / Tobias Schmitz, University of Mainz

3. Introduction: ESR dosimetry
Alanine is the best known ESR dosimeter
Through ionising particles or neutrons radicals are produced in the pellets
Alanine radical
L-α-Alanine
The amount of radicals is measured by electron spin resonance (ESR) – spectroscopy and correlates to the absorbed dose
16th International Congress on Neutron Capture Therapy, Helsinki, Finland / Tobias Schmitz, University of Mainz

4. Relative Effectiveness - RE
ESR dosimeters are calibrated against Co-Gamma-ray source
Radical yield is particle and energy dependent
ESR signal Z
𝑆 𝑅𝑒𝑓 (𝑅 𝑑𝑒𝑡𝑒𝑐𝑡𝑜𝑟 )=
𝑆 𝑍 (𝐷 𝑑𝑒𝑡𝑒𝑐𝑡𝑜𝑟 )
𝑹𝑬= 𝑹 𝒅𝒆𝒕𝒆𝒄𝒕𝒐𝒓 𝑫 𝒅𝒆𝒕𝒆𝒄𝒕𝒐𝒓
(Isoresponse definiton)
D – Dose
R – Response
Dose
𝑅 𝑑𝑒𝑡𝑒𝑐𝑡𝑜𝑟
𝐷 𝑑𝑒𝑡𝑒𝑐𝑡𝑜𝑟
16th International Congress on Neutron Capture Therapy, Helsinki, Finland / Tobias Schmitz, University of Mainz

5. 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, (2010)
16th International Congress on Neutron Capture Therapy, Helsinki, Finland / Tobias Schmitz, University of Mainz

6. Alanine results 𝑅𝐸 (𝑛,𝑝) =0.56 𝑅𝐸 𝛾 =1 →𝟎.𝟖𝟔> 𝑹𝑬 𝒕𝒐𝒕𝒂𝒍 >𝟎.𝟗𝟑
(Presented at 15th ICNCT in Tsukuba, Japan, September 2012)
Alanine measurement
FLUKA dose response
MCNP dose response
𝑅𝐸 (𝑛,𝑝) =0.56
𝑅𝐸 𝛾 =1
→𝟎.𝟖𝟔> 𝑹𝑬 𝒕𝒐𝒕𝒂𝒍 >𝟎.𝟗𝟑
16th International Congress on Neutron Capture Therapy, Helsinki, Finland / Tobias Schmitz, University of Mainz

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 the
alanine detector (incl. determination of RE factors)?
16th International Congress on Neutron Capture Therapy, Helsinki, Finland / Tobias Schmitz, University of Mainz

8. ESR dosimeters Dosimeter materials: Calcium carbonate 𝑪𝒂 𝑪𝑶 𝟑
Lithium formate 𝑳𝒊(𝑯𝑪𝑶𝑶)∙ 𝑯 𝟐 𝑶
Used as pressed pellets:
Diameter: 5 mm
Height: mm
Irradiation in PMMA phantom
10 Pellets on central length axis
16th International Congress on Neutron Capture Therapy, Helsinki, Finland / Tobias Schmitz, University of Mainz

9. TRIGA Mark II Mainz – Thermal Column
Reactor:
Isotropic field of thermal neutrons:
Neutron flux (100 kW): 2 · 1010 n/(cm2s)
Gamma flux (100 kW): 1 · 1010 γ/(cm2s)
FLUKA plane source
Simulated build-up
Phantom position
16th International Congress on Neutron Capture Therapy, Helsinki, Finland / Tobias Schmitz, University of Mainz

10. ESR readout: Lithium formate
Waldeland et al; Rad Meas 46(2011)
Medium line width
60Co Photons: 1.49 mT
Neutrons: mT
16th International Congress on Neutron Capture Therapy, Helsinki, Finland / Tobias Schmitz, University of Mainz

11. ESR results: Calcium carbonate
Identical dominant radical species
No line-broadening:
→ No dose due to medium or high LET particle
ESR measurement
FLUKA absorbed dose
16th International Congress on Neutron Capture Therapy, Helsinki, Finland / Tobias Schmitz, University of Mainz

12. Lithium formate inside boron shielding
ESR measurement
FLUKA absorbed dose
16th International Congress on Neutron Capture Therapy, Helsinki, Finland / Tobias Schmitz, University of Mainz

13. FLUKA results: Lithium formate
ESR measurement
FLUKA absorbed dose
ESR measurement
FLUKA absorbed dose
16th International Congress on Neutron Capture Therapy, Helsinki, Finland / Tobias Schmitz, University of Mainz

14. FLUKA results: Lithium formate
Calcium carbonate
16th International Congress on Neutron Capture Therapy, Helsinki, Finland / Tobias Schmitz, University of Mainz

15. FLUKA results: Lithium formate
ESR measurement
FLUKA absorbed dose
ESR measurement
FLUKA absorbed dose
Calculated RE = 0.36
(Experimental RE = 0.42) t α
Relative Fluence (cm-2) t α
Particle spectra inside the detector
RE factors according to
track structure theory
16th International Congress on Neutron Capture Therapy, Helsinki, Finland / Tobias Schmitz, University of Mainz

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

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

18. Thank you for your attention!
Kiitän teitä huomiostanne!
Thank you
for your attention!
Cathedral in Mainz, Germany

19. 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 *
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.
16th International Congress on Neutron Capture Therapy, Helsinki, Finland / Tobias Schmitz, University of Mainz

20. Comparison of prim. Photon doses
Calculated with FLUKA:
Calcium formate
Ammonium formate
Lithium formate
Mass Energy Absorbtion Coefficient Ratios:
𝜇 𝑒𝑛 𝜌 𝑥 𝜇 𝑒𝑛 𝜌 𝑦
Calcium f. / Ammonium f.:
1.36
Calcium f. / Lithium f.:
1.33
16th International Congress on Neutron Capture Therapy, Helsinki, Finland / Tobias Schmitz, University of Mainz

21. Primary particles in the thermal column
Neutron flux and spectrum
Gamma flux and spectrum
GeV
GeV
16th International Congress on Neutron Capture Therapy, Helsinki, Finland / Tobias Schmitz, University of Mainz

22. Pellet read-out 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
16th International Congress on Neutron Capture Therapy, Helsinki, Finland / Tobias Schmitz, University of Mainz

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