Retrospective Dosimetry Based on Long Lived Free Radicals Harold Swartz, M.D., Ph.D. Geisel Medical School at Dartmouth
Region near Fukushima reactor site Dose distribution from fallout about May 1, 2011
Map shows the radiation dose that would be received by people in the first year following the release of radioactive material from the k h h l ' d l f l
Local expert advising citizens about concerns if return to homes
Problems faced by the Japanese people • Effects of the earthquake • Effects of the tsunami • Concerns about radiation exposures • Loss of confidence in the reliability of governmental authorities and maybe also other sources of authority
EPR Dosimetry Could Help! • Predictions as to possible exposures if return to homes are likely to be generally accurate, but subject to local variations. • The trust of the people in guidance from government is likely to be limited. • Periodic direct measurements of dose for each person by EPR would be reassuring. • Potential to fill in gaps in estimating total dose, e.g., during first weeks when monitoring was not fully implemented. • Lower limit of detection could be increased by: – Longer measurement times – Obtaining background measurements from individuals who are at higher risk for exposure in the future
Electron Paramagnetic Resonance (EPR or ESR) as a Diagnostic for Large-Scale Radiation Incidents Scenario: •Improvised nuclear device (10 kT) in metropolitan area •Potential casualties from radiation exposure > 100,000 Designed to Meet Need for Dosimetry Diagnostics for triage • Rapid classification of patients into low (< 2 Gy) and high (≥ 2 Gy) exposure • Potential additional use: Quantitative assessment of dose across the entire plausible dose range 7
In Vivo EPR Tooth Biodosimetry • Physical basis of EPR is similar to MRI (EPR uses the magnetic moment of unpaired electrons instead of magnetic nuclei; magnetic field is 100 times lower for our dosimeter) • Ionizing radiation generates large numbers of unpaired electron species (carbonate anion radicals) in enamel • Occurs immediately and persists in teeth for thousands of years • Magnitude of the signal is proportional to the dose of radiation • Independent of dose rate and type of radiation (except neutrons) • Phenomenon has been recognized for decades • Potential for dosimetry was first identified >40 years ago • Ex vivo use of EPR dosimetry has a long history – Used for dosimetry (Chernobyl and Japan) – Used for archeological dating • Potential for in vivo use demonstrated more than 10 years ago 8
In Vivo Dosimetry by Electron Spin Resonance Spectroscopy John M. Brady, Norman O. Aarestad and Harold M. Swartz Department of Biophysics, Division of Nuclear Medicine, Walter Reed Army Institute of Research, Walter Reed Army Medical Center, Washington, D.C. 20012 Abstract — Several tissues, especially hard tissues, showed persistent electron spin resonances following in vivo or in vitro irradiations. The resonances had a linear relation to dose. Measurements in rat teeth detected responses at less than 100 rads of 60 Co irradiation. The method appears to be applicable for dosimetry of accidental irradiations, especially X- or gamma-ray exposures. DOCUMENTING LONG HISTORY OF FIELD AND OUR INVOLVEMENT Health Physics 1968 . Vol. 15, pp. 43-47. 9
Clinical in vivo EPR Spectrometer L-band 1.2GHz EPR Spectrometer Air-gap between the magnet is Permanent magnet :420 gauss. The loop 50cm. Human body can be held was fixed on the human teeth. A stable between the magnet. The whole free radical, PDT( Perdeuterated ( 15 ) N - body measurement can be possible Tempone ) is attached at the loop of the at the lying down position. resonator as a reference signal.
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Calibration curve of EPR signal intensity (ex-vivo) The teeth without any irradiation have signals, “ background “ To measure the accurate dose (RIS) by this system, the level of the back ground should be estimated.
Goals for the Device to be Produced by the Contract • Based on EPR dosimetry of incisor teeth in the mouth • Transportable to any site and capable of operating with emergency power systems • Can make the measurements at any time from immediately after the event to any time afterwards • Will dependably screen for exposures of >2 Gy in 5 minutes or less – will be accomplished through a SEP of ≤ 0.5 Gy • Will be operable by non-expert operators • Product will be ready for immediate manufacturing in sufficient quantities to meet the national needs • Will have complied with all aspects of the FDA approval process 13
Feasibility of In Vivo Measurements, using Existing Deployable EPR Dosimeter • In vivo measurements of upper incisor teeth • Uses the current version of the instrument and established methods to measure with EPR – 59 total measurements in 46 people – 18 measurements in 11 TBI patients (0 Gy x 2, 1.5 Gy, 2 Gy x 12, 12 Gy x 3). – Resulting in vivo calibration curve with 1.25 Gy SEP For each subject, 3 -5 independent sets of data were collected, data collection for each set required 60 seconds and the results from the sets were averaged to provide a single dose estimate. Illustrates the ability to make measurements in TBI patients and the current state of the art using dosimetry based on incisors measured in vivo 14
Major Components*: 1. Magnet, 2. Microwave (cell phone frequency), 3. The Resonator that is placed on tooth *associated electronics/software not pictured 2/21/2013 15
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Current version of tooth dosimeter operated in field The operators are Ruhong Dong, M.D., D.D.S. and Ben Williams, Ph.D. (Associate director of the EPR Center) 17
Other EPR Dosimetry under development • Based on same principle, using the person’s tissues as the dosimeter • Use of nail clippings • Measurements of nails in vivo • Advanced methods for measuring dose in teeth 18
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