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Electron paramagnetic resonance dosimetry for dose reconstruction

#B-1194


Development of Methodical Support and Software for Reconstruction of Individual Absorbed Doses by Tooth Enamel Using Electron Paramagnetic Resonance

Tech Area / Field

  • MED-DID/Diagnostics & Devices/Medicine
  • ENV-EHS/Environmental Health and Safety/Environment
  • ENV-MIN/Monitoring and Instrumentation/Environment

Status
3 Approved without Funding

Registration date
16.11.2004

Leading Institute
Belarusian State Medical University, Belarus, Minsk

Collaborators

  • Forschungszentrum für Umwelt und Gesundheit GmbH (GSF) / Institut für Strahlenschutz, Germany, Neuherberg\nNational Institute of Health, Italy, Rome\nOkayama University of Science, Japan, Okayama

Project summary

Purpose of the Project – development of techniques evaluating the contribution to the dose load of diagnostic X-ray irradiation and mechanical processing during the dental treatment of teeth and creation of the software for reconstruction of inpidual absorbed doses on the base of non-linear simulation of EPR spectra of teeth enamel. Demonstration of the developed technology.

State of the art in the field of the Project. The knowledge of inpidual absorbed doses is essential for the environmental radiation monitoring; prediction of radiation effect consequences and detection of the risk group in need of the immediate thorough medical examination. Retrospective reconstruction of inpidual doses in emergency situations is an extremely complicated problem. In Belarus, this problem acquired especial significance following the Chernobyl accident. Method of electronic paramagnetic resonance (EPR) by tooth enamel [Pass et al., 1985; Wieser et al., 1988; Ikeya, 1994; Bougai et al., 2002] is one of perspective approaches of solving this problem. In such inpidual dosimeter, the information about the dose is being read by EPR spectra of tooth enamel. The determined dose is equivalent to the dose evaluated for the whole body.
Currently, except the main components – the native and radiation signals, a hidden signal is supposed to be present in EPR spectra of tooth enamel [Wieser et al., 2000]. Our findings show that this signal may be formed in the process of friction during dental treatment of teeth [Kirillov et al., 2002]. Since the mechanical and the radiation signals are in the same spectral field, their superposition leads to overestimation of the reconstructed dose. To assess the contribution of the mechanical component to the dosimetric signal, they should be separated. To separate the native and radiation components, most investigators use linear simulation of EPR spectra by 3–4 standard lines [Egersdorfer et al., 1996; Onori et al. 2000]. But it is well known that for adequate linear approximation of curves, the number of basis lines is to tend to infinity [Hamming, 1962]. At the same time, non-linear simulation makes it possible to reach good results with the limited number of basis lines, which is most important in practice. With the help of non-linear simulation it is possible to separate the lines located in one spectral field. We have developed recently the software allowing non-linear simulation by two components: native and radiation [Dubovsky, Kirillov, 2001]. To assess the contribution from the mechanical component to the dosimetric signal, it is necessary to conduct simulation of EPR spectra by three lines describing the native, radiation and mechanical components. The given software will involve the reconstruction of absorbed doses, using the technique of additional irradiation [Wieser et al., 2001]. A number of investigators apply the technique of dose reconstruction without using additional irradiation. In this case, standard lines (the same for all enamel samples) are used to separate the dosimetric signal [Haskell et al., 1999]. At the same time, we have shown that taking into account the inpidual line shape, in particular, that of the native signal affects significantly the value of the determined dose [Dubovsky, Kirillov, 2000]. Therefore, the software for correct dose reconstruction without additional irradiation should be developed on the base of non-linear simulation which allows due account of the shape for all the lines of EPR spectra.
It is not possible to assess the contribution from the diagnostic X-ray radiation to the total dose formed due to the combined -and X-ray radiation with the help of spectra simulation, since spectral characteristics of their EPR signals are identical [Aldrich, Pass, 1986; Iwasaki et al., 1991]. To evaluate the contribution from the diagnostic X-ray radiation to the dosimetric signal, correction factor should be introduced, which can be determined empirically taking into account X-ray energy and power (know-how).
Thus, despite a considerable progress in the field of EPR-dosimetry, there still remain a number of unsolved problems. In particular, it concerns mechano-induced paramagnetic centers formed in tooth enamel due to friction during the dental treatment, which results in overestimation of the reconstructed dose. The diagnostic X-ray radiation of teeth creates a serious obstacle. The world-known approach based on linear simulation of EPR spectra does not allow correct deconvolution of the dosimetric signal. All the above-mentioned testifies to actuality of the proposed work within the project.

Impact of the Proposed Project on the Progress in the Field of the Development. The technique developed in the process of project implementation will allow an improvement in accuracy and efficiency of dose reconstruction and contribute to further progress in the field of unification and optimisation of the environmental radiation monitoring.

The Project Participants. The project will be implemented by scientists, most of which participated in the research programs of the military and industrial complex of the former USSR in the field of nuclear, biological and chemical weapon, which will allow their alternative employment. Of 16 scientists, 4 are Doctors of Sciences and 4 – PhDs. The use of their professional knowledge in the dosimetry, EPR-spectroscopy and programming for implementation of the given project will make an important contribution to solving the problems of the environmental radiation monitoring and practical health care.

Expected Results. In the course of implementation of 4 project tasks, the following results are expected to be achieved:
§ The technique evaluating the contribution from the mechano-induced component to the dose load with combined radiation and mechanical effect on tooth enamel will be developed.
§ The technique evaluating the contribution from the diagnostic X-ray radiation to the total dose with combined effect of - and X-ray radiation on tooth enamel will be developed.
§ A software package will be created to reconstruct inpidual absorbed doses by means of non-linear simulation of complex EPR spectra of tooth enamel for separation to components describing the native, mechano- and radiation-induced signals.
§ The developed technique will be demonstrated on tooth samples of citizens of Belarus affected by the Chernobyl accident.
Solving of the above-described tasks will result in the development of a new technique for adequate reconstruction of inpidual absorbed doses by EPR-spectra of tooth enamel. This technique will make it possible to take into account the contribution from the diagnostic X-ray radiation and the mechanical processing of teeth to the dose load, which in its turn, will allow an increase in accuracy and efficiency of dose reconstruction in a wide range of values.

The Field of the Application of the Results. The developed technologies will be widely used in the field of health care (to reveal the risk groups in need of immediate medical care), environmental protection (radioecological monitoring), dosimetry (reconstruction of inpidual absorbed doses), anthropology and paleontology (EPR dating).


Meeting ISTC Goals and Objectives. The project corresponds to the ISTC goals and objectives because:
§ Weapon scientists who are project participants, will be given an opportunity to transfer their efforts to peace activities, in particular to the problems of radiation monitoring;
§ Project participants will be integrated to the International Scientific Society, taking part in International Conferences and workshops devoted to the problems of radiation monitoring;
§ It supports fundamental and applied studies and the development of technologies for peaceful purposes, especially in the field of reconstruction of inpidual absorbed doses;
§ It contributes to solving the national problem – liquidation of the Chernobyl accident consequences, and international technical problems – monitoring of contaminated with radioactive waste territories;
§ It supports the transition of project participants to the market economy by developing the software package, which will be in demand in the institutions dealing with the problems of EPR dosimetry in different countries.

Scope of Activities. Project duration is 36 months. 18 people from the same institution – Belarusian State Medical University, of which 7 are weapon scientists, will participate in the project implementation. Total project effort is 7227 person *days, of which 4125 person*days is total project effort of weapon scientists. The project is pided into 4 interrelated tasks. Task 1 includes the development of the technique for evaluating the contribution from mechano-induced radicals to the dose load. Task 2 involves the development of the technique for evaluating the contribution from the diagnostic X-ray radiation to the total dose. Based on tasks 1 and 2, two instructions for application of these techniques will be developed and approved by the Ministry of Health. Both techniques will be used for the development of two software packages aimed at dose reconstruction by the EPR spectra of tooth enamel while solving task 3. The developed techniques will be demonstrated during the implementation of task 4 involving the reconstruction of doses in citizens of Belarus affected by the Chernobyl accident. About 1000 doses will be reconstructed and scientific analysis will be performed.

Role of Foreign Collaborators. Collaborators of the proposed project expressed their will to participate in:
§ the development of the project work plan;
§ the exchange of information;
§ consultations;
§ joint workshops and conferences;
§ joint studies within the project themes;
§ cross verification of the obtained results by means of mutual blind testing of the software using the teeth samples irradiated by nominal doses unknown for the testing party.

Technical Approach and Methodology. Project participants have a great experience in the field of EPR-spectroscopy and processing of signals. In particular, it was previously revealed that superposition of mechanical and radiation signals leads to an overestimation of the reconstructed dose. The software was developed, which allows with the help of non-linear simulation a separation of a complex EPR spectrum in two components describing the native and radiation signals. Due account of the line shape has been found to be important during the signal processing. Significance and accuracy of the applied approaches to the dose estimate was confirmed by the results of inter-comparison. Task 1: spectral analysis of the radiation, mechanical, thermal and native signals shape will be performed by deconvolution of complex EPR spectra of tooth enamel. The technique evaluating the contribution from mechanical signals to the reconstructed dose will be developed. Task 2: the shape and the intensity of the formed signals will be studied for combined effect of X- and -radiation on tooth enamel. Taking into account these data, as well as X-ray energy and power the technique evaluating the contribution from the diagnostic X-ray radiation to the total dose will be developed. Task 3: the software for dose reconstruction, using non-linear simulation of EPR spectra will be created. The software package will be written in Delphi for Windows 98, NT, XT and will operate in the automatic mode. Task 4: the techniques developed in tasks 1-3 will be demonstrated in the process of dose reconstruction by tooth enamel EPR spectroscopy in the population of Belarus mostly affected by the Chernobyl accident consequences.


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