Department of Physics

1

EPR/alanine dosimetry

• The amino acid alanine H3N-CH(CH3)-COO-
• near tissue equivalence Zeff(water) 7.51,
  Zeff(ala) 6.58
• high radiation chemical yield
• linear radiation response over 3-4 decades
• near invariant response to
• variations in photon energy
• minor temperature variations
• variations in radiation quality (low LETs)
• other variations in ambient conditions
• high stability of radiation products

Department of Physics University of Oslo

PTB-Seminar 2006
2

EPR/alanine dosimetry

• Sensitivity
• best lower dose limit for obtaining sD lt 3 D
  2-3 Gy
• (Nagy et al., Appl. Radiat. Isot.
  56, 917 (2002))
• limited by extensive hyperfine coupling,
  orientational dependencies and background signals
• too low for many low-dose applications

Department of Physics University of Oslo

• Searching for alternative materials
• retaining the excellent dosimetric properties of
  alanine
• better dosimetric sensitivity than alanine

PTB-Seminar 2006
3

Department of Physics University of Oslo

Lithium Formate as a Low-Dose EPR Radiation
Dosimeter
Einar Sagstuen1, Eirik Malinen1,2, Tor Arne
Vestad1,2, Einar Waldeland1,2 and Eli Olaug
Hole1 1 Department of Physics, University of
Oslo 2Institute for Cancer Research, The
Norwegian Radium Hospital
EPR-Labotratory
PTB-Seminar 2006
4

Alternative materials
Department of Physics University of Oslo

PTB-Seminar 2006
5

Alternative materials
Department of Physics University of Oslo

PTB-Seminar 2006
6

Lithium formate, EPR spectrum

• The EPR spectrum of irradiated LiFo exhibits
• a single resonance line
• a peak-to-peak (pp) linewidth of 1.5 mT

Department of Physics University of Oslo

60Co 5 Gy
PTB-Seminar 2006
7

Lithium formate, dose response

• The dose response of irradiated LiFo is
• linear over a dose range comparable to alanine
• more sensitive than alanine with a factor of
  about 6
• (power and modulation are set to values giving
  50 of max intensity for each compound)

Department of Physics University of Oslo

60Co
PTB-Seminar 2006
8

Lithium formate, dose response

• Sub-gray doses are easily measured
• 7 minutes scan time per spectrum
• single measurement sD 4 at 0.4 Gy

Department of Physics University of Oslo

60Co, 5 samples
Dual-mode TE104 cavity, 40 mW, 1.25 mT
Vestad et al., 2003. Appl. Radiat. Isotop. 59, 181
PTB-Seminar 2006
9

Lithium formate, dose response

• Single-scan low-dose measurement
• using a Bruker EleXsyS EPR spectrometer with a
  SuperX cavity

Department of Physics University of Oslo

1 mT
60Co
PTB-Seminar 2006
10

Lithium formate, microwave power

• Favorable microwave power and modulation
  amplitude properties (TE104 EPR cavity)
• No saturation below 200 mW _at_ ?m 100 kHz (rapid
  passage)
• No excessive overmodulation up to Bm 3 mT

Department of Physics University of Oslo

Alanine LiFo
60Co 10 Gy
Vestad et al., 2003. Appl. Radiat. Isotop. 59, 181
PTB-Seminar 2006
11

Lithium formate, radical stability
Apparent short-term radical stability comparable
to that of alanine
Department of Physics University of Oslo

?t 15 min Mn reference
220 kV 10 Gy
Vestad et al., 2003. Appl. Radiat. Isotop. 59, 181
PTB-Seminar 2006
12

Lithium formate, radical stability
..although possible variations have been observed
Department of Physics University of Oslo

• Ongoing experiments using
• 6 photon energies (60 kV 16 MV)
• 4 different doses (5 Gy 5 kGy)
• 4 different relative humidities (10 - 80)

60Co
Vestad ,2005. PhD thesis, Univ. Oslo
PTB-Seminar 2006
13

Lithium formate, TLD comparison
A comparison with TL dosimeters (TD 100 rods) in
the dose range 0.47 2.4 Gy
Department of Physics University of Oslo

All photon energies
EPR Mean sD 4.3 1.1 TLD Mean sD 4
(uncorr), 1.2 (corr)
? 60Co ? 6 MV
TE104, 3 samples.,50 mW, 1.5 mT, 3.5 min
Vestad et al., 2004. Phys. Med. Biol. 49, 4701
PTB-Seminar 2006
14

Lithium formate, photon energy dependency

• similar energy dependencies for LiFo and TL
  dosimeters
• comparable to that of the EPR/alanine dosimetry
  system. (Bergstrand et
  al., 2003, Phys. Med. Biol. 48, 1753)

Department of Physics University of Oslo

Vestad et al., 2004. Phys. Med. Biol. 49, 4701
PTB-Seminar 2006
15

Lithium formate, radical structures

• Single crystal EPR/ENDOR measure-ments shows
  that the dominating radical species at 295 K is
  CO2-
• CO2- formed by deprotonation of an initial
  oxidation product

Department of Physics University of Oslo

Vestad et al., 2004. Phys. Chem. Chem. Phys. 6,
3017
PTB-Seminar 2006
16

Lithium formate, radical structures
Simulations of polycrystalline spectra show that
the CO2- radical accounts for the majority of
all radicals at 295 K.
Department of Physics University of Oslo

Vestad et al., 2004. Phys. Chem. Chem. Phys. 6,
3017
PTB-Seminar 2006
17

Lithium formate, radical structures
Single crystal measurements
Department of Physics University of Oslo

Additional components appear after storage at
elevated temperatures for 8 months

• Red spectra after storage
• two minority resonances
• a doublet
• a singlet.

Sanderud et al., 2006. In preparation
PTB-Seminar 2006
18

Lithium formate, radical structures

• Structure for singlet (Radical II) not yet
  known.
• The doublet (Radical III) is CO22- -O-(CH)O

Department of Physics University of Oslo

Sanderud et al., 2006. In preparation
PTB-Seminar 2006
19

Lithium formate, radiation quality
Microwave saturation behavior of LiFo, 20 Gy
(scaled plots)
Department of Physics University of Oslo

EleXsyS, TE104 w/o leveller Bm 0.3 mT ?m 10 kHz
Waldeland, Master Thesis 2005, Dept. Physics,
University of Oslo
PTB-Seminar 2006
20

Lithium formate, radiation quality
Analysis of saturation curves ? relaxation times
Department of Physics University of Oslo

Waldeland, Master Thesis 2005, Dept. Physics,
University of Oslo
PTB-Seminar 2006
21

Lithium formate, radiation quality
Corresponding linewidth-variation in EPR spectra
(normalized spectra)
Department of Physics University of Oslo

?-irradiated 14N7 irradiated
Magnetic Field (mT)
Waldeland, Master Thesis 2005, Dept. Physics,
University of Oslo
PTB-Seminar 2006
22

Lithium formate, radiation quality
Peak-to peak amplitude/mass (a.u.)
Mean response coeffisient (protons) 0.905 0.021
Department of Physics University of Oslo

Dose to water (Gy)
Mean response coeffisient (electrons) 0.984
0.023
Waldeland, Master Thesis 2005, Dept. Physics,
University of Oslo
PTB-Seminar 2006
23

Lithium formate, radiation quality

• pp linewidth increase with dose
• Mean pp linewidth increase about 10.6
• Mean response coeffisient (14N7)
• pp 0.654 0.030
• area 0.712 0.031

Department of Physics University of Oslo

Dose to water (Gy)
Dose to water (Gy)
Neutron dose very uncertain Peak-to-peak (pp)
linewidth increase about 4.5
Waldeland, Master Thesis 2005, Dept. Physics,
University of Oslo
PTB-Seminar 2006
24

Lithium formate, Summary

• Zeff 7.31

Department of Physics University of Oslo

• Single line EPR spectrum (1.5 mT)

• Linear dose response between 0.2 Gy and gt 1 kGy

• Detection limit lt 0.1 Gy

• Favorable microwave power saturation and field
• modulation properties

• Good radical stability

• Photon and electron energy dependence comparable
  
• to that of alanine

• One dominating radical species, CO2-

• Larger LET dependencies for protons and
  nitrogen ions

PTB-Seminar 2006
25

Acknowledgements
Thanks are due to Mr. Efim Brondz, University
of Oslo Prof. Erik Grusell, Uppsala
University Prof. Per Hoff, University of
Oslo Dr. Peter Höfer, Bruker BioSpin GmbH Prof.
Anders Lund, Linköping University Prof. Jean
Maruani, Lab. de Chimie et Physique, Paris Dr.
Audun Sanderud, University of Oslo Dr. Bo
Stenerlöv, Uppsala University for assistance
with experiments and instrumentation, and
valuable discussions.
Department of Physics University of Oslo

PTB-Seminar 2006
26

Department of Physics University of Oslo

PTB-Seminar 2006
27

EPR/alanine dosimetry
Eirik Malinen
Eva S. Bergstrand
Department of Physics University of Oslo

Tor Arne Vestad
Einar Waldeland
PTB-Seminar 2006