Presentation on theme: "Electron Paramagnetic Resonance Biodosimetry in Teeth and Fingernails"— Presentation transcript:
1Electron Paramagnetic Resonance Biodosimetry in Teeth and Fingernails A. Romanyukha1,2, R.A. Reyes2, F. Trompier3, L.A. Benevides1, H.M. Swartz41Naval 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
2Outline EPR dosimetry basics In vitro X and Q dosimetry in tooth enamelIn vivo tooth L-band dosimetryEPR dosimetry in fingernailsConclusions
3What 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.
4EPR: 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.
6Typical 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, fingersX9.50.33mg (solid)K200.7010 – 30 mg (solid)Q351.222 – 10 mg (solid)W953.300.25 – 1 mg (solid)
7EPR 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 tissuesFinger- and toenailsFinger- and toenails
8Characteristics of EPR dosimetry Non-invasiveBased on a physical processNot affected by biological processes such as stressNot affected by simultaneous damage that is likely to occur with irradiation such as wounds & burnsApplicable 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
9In vitro measurements in tooth enamel samples (X and Q-bands)
10Extracted teeth can be available for in vitro EPR measurements
11Validation and Standardization Four successful International Dose Intercomparisons with totally more than 20 participating labsICRU, Retrospective Assessment of Exposures to Ionizing Radiation. Report 68 (Bethesda, MD: ICRU).IAEA, 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.
12Steps of the method Tooth collections Tooth enamel sample preparation EPR measurements of radiation responseCalibration of EPR radiation response
16EPR 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, Japan1945100GyNakamura et al., Int. J. Radiat. Biol. 73, (1998)Mayak nuclear workers, Russia~100GyWieser et al., Radiat. Env. Biophys. 2006Romanyukha et al., Health Phys. 78, (2000)Techa riverside populationGyRomanyukha et al., Health Phys., 81, (2001)Romanyukha et al., Radiat. Environ. Biophys., 35, (1996)Eye-witnesses of Totskoye nuclear test, Russia195410GyRomanyukha et al., Radiat. Prot. Dosim., 86, (1999).Chernobyl clean up workers, Ukraine1986660GyChumak et al., Radiat. Prot. Dos. 77, (1998)Population of areas contaminated by Chernobyl fallout, Russia2500~ 0.1 GyStepanenko et al., Radiat. Prot. Dos. 77, (1998)Semipalatinsk population1950s32Romanyukha et al., Appl. Mag. Res.., 22, (2002)
17ConclusionEPR 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
18exfoliated/extracted teeth Alternatives toexfoliated/extracted teethL-band (1.2 GHz) non-Invasive in vivo measurementsQ-band (35 GHz) measurements in enamel “biopsy” samples (~2 mg) with followed up tooth restoration
19Q-band (35 GHz) measurements in enamel “biopsy” samples (~2 mg) with followed up tooth restoration
20Description of Q-band feasibility test Tooth enamel powder samples for test: 0; 0.1 Gy; 0.5 Gy; 1 Gy; 3 Gy; 5 GyEach sample was recorded 3 times in X (100 mg) and Q bands (2, 4 mg)Recent publicationRomanyukha A. et al. Q-band EPR biodosimetry in tooth enamel microprobes: Feasibility test and comparison with X band. Health Physics. 93, , (2007).
21X-band spectrum vs Q-band spectrum X-band (100 mg), 0.1 GyQ-band, (4 mg) 0.1 GyQ-band has significantly lesser amount of the sample required for dose measurementsQ-band has significantly better spectral resolution of dose response
23Dental 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.BiopsyWhole ToothIn collaboration with B. Pass, P. Misra, T. De (Howard University)
24Q-band biopsy experiment Tooth enamel biopsy sample 2.2 mg was irradiated 4 times to the same dose GyAfter 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
25Angle 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.
26Spectra 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 dosesDose dependences for average, maximum, minimum and median values of radiation response at each dose
27Results of attempt to reconstruct 4. 3 Gy in biopsy sample (2 Results of attempt to reconstruct 4.3 Gy in biopsy sample (2.2 mg) using different approachesApproachResult of linear back extrapolationAverage values5.5 ± 0.8 GyMaximum values7.3 ± 3.6 GyMinimum values5.4 ± 0.7 GyMedian values5.4 ± 1.4 Gy
28Preliminary 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 reconstructionUse 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, respectivelyA possible reason for some dose offset (~1 Gy) is a slope of a base line of the spectra for this sampleA possible solution is to apply base line correction to spectra before measurements of peak-to-peak amplitude of radiation response
30Recent 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, (2005)Swartz H.M. et al. In Vivo EPR Dosimetry to Quantify Exposures to Clinically Significant Doses of Ionizing Radiation. Radiat. Prot. Dosim. 120, (2006).Swartz H.M. et al. In Vivo EPR for Dosimetry. Radiat. Meas. 42, , (2007).
31L-band (1 GHz) of microwaves is better for realization of in vivo EPR than standard X-band (9 GHz) because it hasGreater tolerance for the presence of waterRelatively large sample volume sufficient for whole tooth.
32Components of in vivo EPR spectrometer Resonators that will probe teeth in vivoMagnet system that can comfortably and effectively encompass the human headSoftware for EPR dose response determinationDose calibration for in vivo L-band measurements
35In 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)
38Dose-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.
39EPR 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.
40Finger-and toenails facts Typical available amounts of nail parings are up to 120 mg for fingernails and up to 160 mg for toe nailsNails grow all the time, but their rate of growth slows down with age and poor circulationFingernails 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 edgeToenails grow about 1 mm per month and take months to be completely replacedThe nails grow faster on your dominant hand, and they grow more in summer than in winterThe 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.
41Recent developmentRomanyukha A. et al. EPR dosimetry in chemically treated fingernails. Radiat. Meas. 42, , (2007).Trompier F. et al. Protocol for emergency EPR dosimetry in fingernails. Radiat. Meas. 42, , (2007).Reyes R.A. et al. Electron paramagnetic resonance in human fingernails: the sponge model implication. To be published in Radiat. Env. Biophys. (2008)
42New 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 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
43Radiation-induced signal in unstressed fingernails RIS spectra obtained by subtraction of BKS spectrum recorded prior irradiationRIS parameters: g= DH=9 G
44Result of dose reconstruction in the sample irradiated to 4 Gy 5 days before reconstruction Reconstructed dose 3.66 Gy, reduction
46Dosimetric properties of fingernails Optimal sample mass is 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)
47Conclusions Part of body EPR band/freq LLD, Gy in vivo/ amount Time stabilityTooth enamelX0.150 – 100 mg106 yrQ2-4 mgToothL3-5In vivoFinger-nails0.5-120-30 mg~2 wks
48AcknowledgementsG. 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
49DisclaimerThe 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.