Electron Paramagnetic Resonance
Biodosimetry in Teeth and Fingernails
A. Romanyukha1,2, R.A. Reyes2, F.
Trompier3, L.A. Benevides1, H.M. Swartz4
1Naval
Dosimetry Center, 8901 Wisconsin Ave., Bethesda, MD, 20889, USA,
Services University, 4301 Jones Bridge Rd., Bethesda, MD, 20814, USA,
3Institut de Radioprotection et de Sûreté Nucléaire, Fontenay-aux-roses, France,
4Dartmouth Medical School, Hanover, NH, 03755, USA
2Uniformed
Outline
•
•
•
•
•
EPR dosimetry basics
In vitro X and Q dosimetry in tooth enamel
In vivo tooth L-band dosimetry
EPR dosimetry in fingernails
Conclusions
What is Electron Paramagnetic
Resonance (EPR) ?
• Non-destructive magnetic resonance technique
used to detect and quantify unpaired electrons.
• Absorption of ionizing radiation generates
unpaired electrons (i.e., paramagnetic centers).
• The concentration of radiation-induced
paramagnetic centers is proportional to the
absorbed dose.
EPR: Fundamentals and Principles
• There is a net absorption
of energy from the
microwave field at
resonance because of a
greater population of
electrons are in the lower
energy state.
• The process is nondestructive because the
population difference
reestablishes itself after
the microwave field is
turned off.
• Thus, the history of
radiation exposure is not
destroyed by EPR
measurements.
Optical Imaging
Electron Resonance
Typical frequencies and wavelengths required
for resonance of a free electron in EPR
measurements
Mw Frequency,
Band GHz
Magnetic Sample size
field, T
L
1.5
0.05
Small animals,
whole human teeth,
fingers in situ
S
3.2
0.11
Whole teeth, fingers
X
9.5
0.33
30 - 1000 mg (solid)
K
20
0.70
10 – 30 mg (solid)
Q
35
1.22
2 – 10 mg (solid)
W
95
3.30
0.25 – 1 mg (solid)
EPR dosimeters for partial body
exposure
Radiation-induced
radicals are stable only in
hard tissues: teeth, bone,
fingernails and hairs.
Depending on mw band
EPR can be measured in
vivo or in vitro using
specially prepared
samples from human
hard tissues
Finger- and toenails
Finger- and toenails
Characteristics of EPR dosimetry
 Non-invasive
 Based on a physical process
 Not affected by biological processes such as stress
 Not affected by simultaneous damage that is likely to occur
with irradiation such as wounds & burns
 Applicable to individuals
 Measurements can be made at any interval after irradiation up
to at least 2 weeks (fingernails) or indefinately (teeth)
 Can provide output immediately after the measurement
 Unaffected by dose rate
 Can operate in a variety of environments
 Systems can be developed so that they can be operated by
minimally trained individuals
In vitro measurements in tooth
enamel samples (X and Q-bands)
Extracted teeth can be
available for in vitro EPR measurements
Validation and Standardization
Four successful International Dose Intercomparisons with
totally more than 20 participating labs
ICRU, 2002. Retrospective Assessment of Exposures to
Ionizing Radiation. Report 68 (Bethesda, MD: ICRU).
IAEA, 2002. Use of electron paramagnetic resonance
dosimetry with tooth enamel for retrospective dose
assessment. International Atomic Energy Agency, Vienna,
IAEA-TECDOC-1331.
EPR dosimetry with teeth is the only method which can
reconstruct external gamma radiation doses (<100 mGy)
individually.
Steps of the method
•
•
•
•
Tooth collections
Tooth enamel sample preparation
EPR measurements of radiation response
Calibration of EPR radiation response
EPR Biodosimetry
(Teeth)
EPR Biodosimetry
(Teeth)
• Hydroxyapatite constitutes:
– ~95% by weight of tooth enamel
– 70-75% of dentin
– 60-70% of compact bones
Romanyukha, et. al, Appl. Radiat. Isot. (2000) and IAEA-TECDOC-1331
EPR Biodosimetry
(Dose Calibration)
EPR Biodosimetry Applications
(Epidemiological Investigations Using Tooth EPR)
Description of
group
Survivors of abombing of
Hiroshima, Japan
Year of
overexposure
Number of
reconstructed
doses
Values of
reconstructed
doses, Gy
Reference
1945
100
0.3-4.0 Gy
Nakamura et al., Int. J. Radiat. Biol. 73,
619-627 (1998)
Mayak nuclear
workers, Russia
1948-1961
~100
0.2-6.0 Gy
Wieser et al., Radiat. Env. Biophys. 2006
Romanyukha et al., Health Phys. 78, 1520 (2000)
Techa riverside
population
1948-1958
~100
0.1-10 Gy
Romanyukha et al., Health Phys., 81,
554-566 (2001)
Romanyukha et al., Radiat. Environ.
Biophys., 35, 305-310 (1996)
Eye-witnesses of
Totskoye nuclear
test, Russia
1954
10
0.1-0.4 Gy
Romanyukha et al., Radiat. Prot. Dosim.,
86, 53-58 (1999).
Chernobyl clean up
workers, Ukraine
1986
660
0 - 2.0 Gy
Chumak et al., Radiat. Prot. Dos. 77, 9195 (1998)
Population of areas
contaminated by
Chernobyl fallout,
Russia
1986
2500
~ 0.1 Gy
Stepanenko et al., Radiat. Prot. Dos. 77,
101-106 (1998)
Semipalatinsk
population
1950s
32
0.3-4.0 Gy
Romanyukha et al., Appl. Mag. Res.., 22,
347-356 (2002)
Conclusion
• EPR X-band (9 GHz) dosimetry in tooth
enamel works excellent (LLD<100 mGy,
time after exposure when dose
measurements are possible from 0.01 hr
to 106 yr.
• But it requires to have extracted or
exfoliated teeth available for preparation of
tooth enamel
Alternatives to
exfoliated/extracted teeth
L-band (1.2 GHz) non-Invasive in vivo measurements
Q-band (35 GHz) measurements in enamel “biopsy”
samples (~2 mg) with followed up tooth restoration
Q-band (35 GHz) measurements in
enamel “biopsy” samples (~2 mg)
with followed up tooth restoration
Description of Q-band
feasibility test
Tooth enamel powder samples for test: 0;
0.1 Gy; 0.5 Gy; 1 Gy; 3 Gy; 5 Gy
Each sample was recorded 3 times in X (100
mg) and Q bands (2, 4 mg)
Recent publication
Romanyukha A. et al. Q-band EPR biodosimetry in tooth enamel microprobes:
Feasibility test and comparison with X band. Health Physics. 93, 631-635, (2007).
X-band spectrum vs Q-band spectrum
X-band (100 mg), 0.1 Gy
Q-band, (4 mg) 0.1 Gy
0.08
0.01
0.00
0.04
EPR signal, a.u.
EPR signal. a.u.
0.06
0.02
0.00
-0.02
-0.01
-0.02
-0.04
-0.03
-0.06
-0.08
3490
3500
3510
3520
Magnetic field, G
3530
3540
-0.04
12060
12080
12100
12120
12140
12160
12180
12200
Magnetic field, G
1. Q-band has significantly lesser amount of the sample required for dose
measurements
2. Q-band has significantly better spectral resolution of dose response
12220
Dose dependence: X vs Q
0.12
X-band, 100 mg sample
1.2
Q-band, 4 mg sample
0.10
EPR radiation response, a.u.
EPR radiation response, a.u.
1.0
0.8
0.6
0.4
0.2
0.0
0.08
0.06
0.04
0.02
0.00
0
1
2
3
Radiation dose, Gy
4
5
0
1
2
3
Radiation Dose, Gy
4
5
Dental Biopsy Technique
 With the enamel biopsy technique a
small enamel chip is removed from a
tooth crown with minimal damage to
the structural integrity of the tooth.
 A high-speed compressed-air driven
dental hand piece is used with
appropriate dental burs for this
purpose.
 Standard techniques for tooth
restoration using light-cured
composite resins rapidly restore the
small enamel defect in the biopsied
enamel surface of the crown.
Whole Tooth
Biopsy
 Preliminary study on discarded teeth
have demonstrated the feasibility of
removing 2 mg enamel chips, the
desired size for sufficient sensitivity In collaboration with B. Pass, P. Misra,
with Q-band EPR dosimetry.
T. De (Howard University)
Q-band biopsy experiment
• Tooth enamel biopsy sample 2.2 mg was
irradiated 4 times to the same dose - 4.3 Gy
• After each irradiation angle dependence (12
positions) of biopsy sample was studied
• Using average, maximum, minimum and median
values of EPR radiation response at each dose
(e.g. 4.3, 8.6, 12.9 and 17.1 Gy) and linear back
extrapolation attempt to reconstruct dose of 4.3
Gy was made
Angle dependence of radiation
response
0.40
Dose = 8.6 Gy
EPR peak-to-peak ampl., a.u.
0.35
0.30
0.25
0.20
0.15
0
50
100
150
200
Angle, degree
250
300
350
Possible approaches:
1. Use average value of radiation
response at each dose;
2. Use maximum value of radiation
response at each dose;
3. Use minimum value of radiation
response at each dose;
4. Use median value of radiation
response at each dose.
Spectra in biopsy sample at different
doses and dose dependences
0.4
4.3 Gy
8.6 Gy
12.9 Gy
17.1 Gy
0.2
0.1
0.0
-0.1
Average
Maximum
Minimum
Median
0.50
0.45
Radiation response, a.u.
EPR dose signal, a.u.
0.3
0.55
0.40
0.35
0.30
0.25
0.20
0.15
-0.2
0.10
12100
12150
12200
Magnetic field, G
Appearance of tooth enamel
spectrum (maximum) of the same
biopsy sample 2.2 mg at different
doses
-2
0
2
4
6
8
10
12
14
Dose, Gy
Dose dependences for average, maximum,
minimum and median values of radiation
response at each dose
Results of attempt to reconstruct 4.3 Gy in
biopsy sample (2.2 mg) using different
approaches
Approach
Average values
Result of linear
back extrapolation
5.5 ± 0.8 Gy
Maximum values 7.3 ± 3.6 Gy
Minimum values
5.4 ± 0.7 Gy
Median values
5.4 ± 1.4 Gy
Preliminary conclusions
• Tooth enamel biopsy spectra have slightly different shape from
powder spectra, they are more narrow and have higher signal-tonoise ratio for the same dose than powder spectra. However
existence of angle dependence for biopsy spectra makes difficult
dose reconstruction. Possible solution is to use average, maximum,
minimum or median values for each dose for dose reconstruction
• Use of average and minimum EPR radiation response values gives
the best results to reconstruct 4.3 Gy, e.g. 5.5 ± 0.8 Gy and 5.4 ± 0.7
Gy, respectively
• A possible reason for some dose offset (~1 Gy) is a slope of a base
line of the spectra for this sample
• A possible solution is to apply base line correction to spectra before
measurements of peak-to-peak amplitude of radiation response
L-band in vivo
Recent publications
•
•
•
Swartz H.M. et al. Measurements of clinically
significant doses of ionizing radiation using
non-invasive in vivo EPR spectroscopy of teeth
in situ. Appl. Radiat. Isot. 62, 293-299 (2005)
Swartz H.M. et al. In Vivo EPR Dosimetry to
Quantify Exposures to Clinically Significant
Doses of Ionizing Radiation. Radiat. Prot.
Dosim. 120, 163-170 (2006).
Swartz H.M. et al. In Vivo EPR for Dosimetry.
Radiat. Meas. 42, 1075-1084, (2007).
• L-band (1 GHz) of microwaves is better for
realization of in vivo EPR than standard Xband (9 GHz) because it has
• Greater tolerance for the presence of water
• Relatively large sample volume sufficient for
whole tooth.
Components of in vivo EPR spectrometer
• Resonators that will probe teeth in vivo
• Magnet system that can comfortably and effectively
encompass the human head
• Software for EPR dose response determination
• Dose calibration for in vivo L-band measurements
Clinical EPR Spectrometers
MAGNETIC FLUX LINES
PATIENT
MAGNET FIXTURES
SPHERE OF HOMOGENEITY
MAGNET COILS
Retrospective Radiation Dosimetry
In Vivo EPR Radiation Dosimetry
Under practical conditions with an
irradiated tooth in the mouth of a
volunteer, the dose dependent signal
amplitude is clearly observed. (Acq.
time = 4.5 minutes/spectrum)
EPR Dose Response
1.5
Slope=0.077, SEP=2.41Gy
Slope=0.073, SEP=1.19Gy
Slope=0.081, SEP=2.67Gy
C #27 #11
P-value difference = 0.4
C #11
0.5
1.0
#22 C #21
#27
Patient V107
Patient V110
C #22
0.0
Average P2P RIS EPR signal in canine teeth
2.0
Dose-response relationship
for two head-and-neck radiation patients
0
5
10
15
20
R adiation dos e giv en, Gy
25
30
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.0
Averaged over 3 days tooth-size adjusted P2P
SE dose prediction = 46 cGy
0
2
5
10
15
30
Radiation given, Gy
Dose-dependence for 6 in vivo teeth, with each tooth irradiated to a different dose and
measured on 3 separate days. Linear regression analysis shows that the standard error
of dose prediction is ± 46 cGy.
EPR biodosimetry in tooth enamel for
partial body dose assessment
• X-band EPR is ready to use for forensic dose
assessment. Could be carried out on compact
and transportable (< 150 kg) EPR spectrometer.
Dose level <100 mGy.
• Q-band biopsy potentially is able to measure
doses < 500 mGy in biopsy tooth enamel
samples 2-4 mg.
• L-band in vivo EPR potentially is able to
measure doses as low as 3 Gy. Needs some
additional development.
Finger-and toenails facts
The major component of
fingernails is a a-keratin. This
protein is built up from three,
long a-helical peptide chains
that are twisted together in a
left-handed coil, strengthened by
S – S bridges formed from
adjacent cisteine groups.
•Typical available amounts of nail parings
are up to 120 mg for fingernails and up to
160 mg for toe nails
• Nails grow all the time, but their rate of
growth slows down with age and poor
circulation
• Fingernails grow at an average of onetenth of an inch (3 mm) a month. It takes 6
months for a nail to grow from the root to the
free edge
• Toenails grow about 1 mm per month and
take 12-18 months to be completely
replaced
• The nails grow faster on your dominant
hand, and they grow more in summer than in
winter
Recent development
Romanyukha A. et al. EPR dosimetry in chemically
treated fingernails. Radiat. Meas. 42, 1110-1113,
(2007).
Trompier F. et al. Protocol for emergency EPR
dosimetry in fingernails. Radiat. Meas. 42, 10851088, (2007).
Reyes R.A. et al. Electron paramagnetic resonance in
human fingernails: the sponge model implication. To
be published in Radiat. Env. Biophys. (2008)
New insights in EPR fingernail
dosimetry
• Fingernails can be considered as a sponge-like
tissue which behaves differently from in vivo
fingernails when mechanically-stressed after
clipping
• Most of previously published results on EPR
fingernail dosimetry were obtained on stressed
samples and not applicable to life-scenario
situation
• Unstressed fingernails have more significantly
stable and sensitive radiation response which
can be measured with EPR
Radiation-induced signal
in unstressed fingernails
1 Gy
5 Gy
8 Gy
0.2
RIS, a.u.
0.1
0.0
-0.1
-0.2
3450
3500
Magnetic field, G
RIS parameters: g=2.0088 DH=9 G
3550
3600
RIS spectra obtained by
subtraction of BKS
spectrum recorded prior
irradiation
Result of dose reconstruction in the
sample irradiated to 4 Gy 5 days before
reconstruction
0.50
0.3
Original signal
after treatment
+2 Gy
+4 Gy
+6 Gy
+11 Gy
0.1
0.45
EPR dose response, a.u.
EPR signal, a.u.
0.2
0.0
-0.1
Parameters of the data fit
with Grun model
Imax=0.5513
D0=7.3 Gy
DE=3.66Gy
Grun model
0.40
0.35
0.30
Grun model:
A = Imax(1 - exp(-(D+DE)/D0)),
where A= EPR dose response,
Imax = max EPR dose response (saturation level),
DE=the dose to be determined
D0= characteristic saturation dose
0.25
-0.2
0.20
3420
3440
3460
3480
3500
3520
3540
Magnetic field, G
3560
3580
3600
0
2
4
6
Added dose, Gy
Reconstructed dose 3.66 Gy, reduction
8
10
12
Variability of dose dependence in
fingernails
0.70
Fresh 1
0.60
A
Old Samples
Fresh 2
Fresh 3
Fresh 4
Amplitude (a.u.)
0.50
Fresh 5
Fresh 6
Fresh 7
0.40
Fresh 8
Fresh 9
Fresh 10
0.30
Old 1
Old 2
0.20
Fresh Samples
Old 3
Old 4
Old 5
0.10
Old 6
Old 7
Old 8
0.00
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21
Dose (Gy)
Old 9
Old 10
Dosimetric properties of
fingernails
• Optimal sample mass is 15-20 mg (nailparings from 2-3 fingers)
• Measurements time 5 minutes (10 scans)
• Achievable lower dose threshold ~ 1 Gy
• RIS fading half-time 300 hr (~2 weeks)
Conclusions
Part of EPR
body
band/freq
Tooth
X
enamel
Tooth
Q
enamel
Tooth
L
LLD,
Gy
0.1
Fingernails
X
in vivo/
Time
amount
stability
50 – 100 mg 106 yr
0.3-0.5 2-4 mg
106 yr
3-5
In vivo
106 yr
0.5-1
20-30 mg
~2 wks
Acknowledgements
G. Burke, E. Demidenko, C. Calas, I.
Clairand, T. De, O. Grinberg, A. Iwasaki,
M. Kmiec, L. Kornak, B. LeBlanc, P.
Lesniewski, P. Misra, C. Mitchell, R.J.
Nicolalde, B. Pass, A. Ruuge, D.A.
Schauer, J. Smirniotopoulos, A. Sucheta,
T. Walczak
Disclaimer
The views expressed in this presentation are those of the
author and do not reflect the official policy or position of
the Navy and Marine Corps Public Health Center, Navy
Bureau of Medicine and Surgery, Department of the Navy,
Department of Defense, or the U.S. Government.
www.Biodose-2008.org