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 Sret Nuclaire, Fontenay-aux-roses, France,4Dartmouth Medical School, Hanover, NH, 03755, USA

OutlineEPR dosimetry basicsIn vitro X and Q dosimetry in tooth enamelIn vivo tooth L-band dosimetryEPR dosimetry in fingernailsConclusions

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.

Alex Romanyukha (AR) - All biological dosimeters are affected by various biogical factors whereas EPR is a pure radiation specific

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.

Optical Imaging

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

Mw BandFrequency, GHzMagnetic field, TSample sizeL1.50.05Small animals, whole human teeth, fingers in situS3.20.11Whole teeth, fingers X9.50.3330 - 1000 mg (solid)K200.7010 30 mg (solid)Q351.222 10 mg (solid)W953.300.25 1 mg (solid)

EPR dosimeters for partial body exposure

Finger- and toenailsRadiation-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

Characteristics of EPR dosimetryNon-invasiveBased on a physical process Not affected by biological processes such as stressNot affected by simultaneous damage that is likely to occur with irradiation such as wounds & burns Applicable to individualsMeasurements can be made at any interval after irradiation up to at least 2 weeks (fingernails) or indefinately (teeth)Can provide output immediately after the measurementUnaffected by dose rateCan operate in a variety of environmentsSystems 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

EPR dosimetry with teeth is the only method which can reconstruct external gamma radiation doses (

Steps of the methodTooth collectionsTooth enamel sample preparationEPR measurements of radiation responseCalibration of EPR radiation response

EPR Biodosimetry(Teeth)

EPR Biodosimetry(Teeth)Hydroxyapatite constitutes:~95% by weight of tooth enamel70-75% of dentin60-70% 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 groupYear of over-exposureNumber of reconstructed dosesValues of reconstructed doses, GyReferenceSurvivors of a-bombing of Hiroshima, Japan19451000.3-4.0 GyNakamura et al., Int. J. Radiat. Biol. 73, 619-627 (1998)Mayak nuclear workers, Russia1948-1961~1000.2-6.0 GyWieser et al., Radiat. Env. Biophys. 2006Romanyukha et al., Health Phys. 78, 15-20 (2000)Techa riverside population1948-1958~1000.1-10 GyRomanyukha et al., Health Phys., 81, 554-566 (2001)Romanyukha et al., Radiat. Environ. Biophys., 35, 305-310 (1996)Eye-witnesses of Totskoye nuclear test, Russia1954100.1-0.4 GyRomanyukha et al., Radiat. Prot. Dosim., 86, 53-58 (1999).Chernobyl clean up workers, Ukraine19866600 - 2.0 GyChumak et al., Radiat. Prot. Dos. 77, 91-95 (1998)Population of areas contaminated by Chernobyl fallout, Russia19862500~ 0.1 GyStepanenko et al., Radiat. Prot. Dos. 77, 101-106 (1998)Semipalatinsk population1950s320.3-4.0 GyRomanyukha et al., Appl. Mag. Res.., 22, 347-356 (2002)

ConclusionEPR X-band (9 GHz) dosimetry in tooth enamel works excellent (LLD

Alternatives to exfoliated/extracted teethQ-band (35 GHz) measurements in enamel biopsy samples (~2 mg) with followed up tooth restorationL-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

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)Description of Q-band feasibility test Recent publicationRomanyukha 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 (100 mg), 0.1 GyQ-band, (4 mg) 0.1 GyX-band spectrum vs Q-band spectrumQ-band has significantly lesser amount of the sample required for dose measurementsQ-band has significantly better spectral resolution of dose response

21.bin

22.bin

Dose dependence: X vs Q

17.bin

20.bin

Dental Biopsy TechniqueWith 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)

Q-band biopsy experimentTooth 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 studiedUsing 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 responsePossible 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 dependencesAppearance of tooth enamel spectrum (maximum) of the same biopsy sample 2.2 mg at different dosesDose 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

ApproachResult of linear back extrapolationAverage values 5.5 0.8 GyMaximum values7.3 3.6 GyMinimum values5.4 0.7 GyMedian values5.4 1.4 Gy

Preliminary conclusionsTooth 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

L-band in vivo

Recent publicationsSwartz 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 X-band (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

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

118.bin

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

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.

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)

New insights in EPR fingernail dosimetryFingernails can be considered as a sponge-like tissue which behaves differently from in vivo fingernails when mechanically-stressed after clippingMost of previously published results on EPR fingernail dosimetry were obtained on stressed samples and not applicable to life-scenario situationUnstressed fingernails have more significantly stable and sensitive radiation response which can be measured with EPR

Radiation-induced signal in unstressed fingernails RIS parameters: g=2.0088 DH=9 GRIS spectra obtained by subtraction of BKS spectrum recorded prior irradiation

Result of dose reconstruction in the sample irradiated to 4 Gy 5 days before reconstructionReconstructed dose 3.66 Gy, reduction

Variability of dose dependence in fingernails

Dosimetric properties of fingernailsOptimal sample mass is 15-20 mg (nail-parings from 2-3 fingers)Measurements time 5 minutes (10 scans)Achievable lower dose threshold ~ 1 GyRIS fading half-time 300 hr (~2 weeks)

Conclusions

Part of bodyEPR band/freqLLD, Gyin vivo/ amountTime stabilityTooth enamelX0.150 100 mg106 yrTooth enamelQ0.3-0.52-4 mg106 yrToothL3-5In vivo106 yrFinger-nailsX0.5-120-30 mg~2 wks

AcknowledgementsG. 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

DisclaimerThe 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