Electron Paramagnetic Resonance Biodosimetry in Teeth and Fingernails

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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, 2Uniformed 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
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Outline

• EPR dosimetry basics
• In vitro X and Q dosimetry in tooth enamel
• In vivo tooth L-band dosimetry
• EPR dosimetry in fingernails
• Conclusions

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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.

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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 non-destructive 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.

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Optical Imaging
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Typical frequencies and wavelengths required for
resonance of a free electron in EPR measurements
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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
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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

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In vitro measurements in tooth enamel samples (X
and Q-bands)
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Extracted teeth can be available for in vitro
EPR measurements
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EPR dosimetry with teeth is the only method which
can reconstruct external gamma radiation doses
(lt100 mGy) individually.
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.
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Steps of the method

• Tooth collections
• Tooth enamel sample preparation
• EPR measurements of radiation response
• Calibration of EPR radiation response

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EPR Biodosimetry(Teeth)
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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
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EPR Biodosimetry(Dose Calibration)
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EPR Biodosimetry Applications (Epidemiological
Investigations Using Tooth EPR)
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Conclusion

• EPR X-band (9 GHz) dosimetry in tooth enamel
  works excellent (LLDlt100 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

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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
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Q-band (35 GHz) measurements in enamel biopsy
samples (2 mg) with followed up tooth
restoration
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Tooth enamel powder samples for test 0 0.1 Gy
0.5 Gy 1 Gy 3 Gy 5 Gy
Description of Q-band feasibility test
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).
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X-band spectrum vs Q-band spectrum
X-band (100 mg), 0.1 Gy
Q-band, (4 mg) 0.1 Gy

• Q-band has significantly lesser amount of the
  sample required for dose measurements
• Q-band has significantly better spectral
  resolution of dose response

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Dose dependence X vs Q
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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.
• Preliminary study on discarded teeth have
  demonstrated the feasibility of removing 2 mg
  enamel chips, the desired size for sufficient
  sensitivity with Q-band EPR dosimetry.

In collaboration with B. Pass, P. Misra, T. De
(Howard University)
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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

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Angle dependence of radiation response
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.
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Spectra in biopsy sample at different doses and
dose dependences
Appearance of tooth enamel spectrum (maximum) of
the same biopsy sample 2.2 mg at different doses
Dose dependences for average, maximum, minimum
and median values of radiation response at each
dose
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Results of attempt to reconstruct 4.3 Gy in
biopsy sample (2.2 mg) using different approaches
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Preliminary conclusions

• Tooth enamel biopsy spectra have slightly
  different shape from powder spectra, they are
  more narrow and have higher signal-to-noise 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

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L-band in vivo
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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).

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• L-band (1 GHz) of microwaves is better for
  realization of in vivo EPR than standard X-band
  (9 GHz) because it has
• Greater tolerance for the presence of water
• Relatively large sample volume sufficient for
  whole tooth.

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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

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Clinical EPR Spectrometers
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Retrospective Radiation Dosimetry
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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)
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EPR Dose Response
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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.
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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 (lt 150 kg) EPR spectrometer. Dose
  level lt100 mGy.
• Q-band biopsy potentially is able to measure
  doses lt 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.

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Finger-and toenails facts

• 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 one-tenth 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

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.
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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,
1085-1088, (2007). Reyes R.A. et al. Electron
paramagnetic resonance in human fingernails the
sponge model implication. To be published in
Radiat. Env. Biophys. (2008)
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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

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Radiation-induced signal in unstressed
fingernails
RIS spectra obtained by subtraction of BKS
spectrum recorded prior irradiation
RIS parameters g2.0088 DH9 G
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Result of dose reconstruction in the sample
irradiated to 4 Gy 5 days before reconstruction
Reconstructed dose 3.66 Gy, reduction
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Variability of dose dependence in fingernails
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Dosimetric properties of fingernails

• Optimal sample mass is 15-20 mg (nail-parings
  from 2-3 fingers)
• Measurements time 5 minutes (10 scans)
• Achievable lower dose threshold 1 Gy
• RIS fading half-time 300 hr (2 weeks)

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Conclusions
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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

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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.

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