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IDEA Informe resumido

Project ID: FIKR-CT-2001-00164
Financiado con arreglo a: FP5-EAECTP C
País: France

Using OEDIPE for creation of VOXEL phantoms

The radiation safety of atomic industry personnel handling radionuclides, Fission and Activation Products (FAP), actinides, etc., inevitably involves radiation monitoring and internal exposure control. The specialized techniques of individual monitoring used at atomic enterprises include the application of dynamic air concentration assessment in the working room air, sampling of human excreta and in vivo monitoring.

Even though, in vivo monitoring presents several advantages such as the possibilities of fast assessment of incorporated activity and high counting efficiency, it has several drawbacks as well. The most crucial one is the need for interpretation of the measurement, to convert the number of pulses in spectrometry channels into retained activity. This process, called calibration is based on the use of plastic phantoms (mannequins) containing a well-known activity. However, the standard reference phantoms do not take into account the individual anatomy of a given subject, the specific size, shape, weight of his (her) organs as well as their placement in the body. To make the things worse, the most radiotoxic incorporated radionuclides (such as 239Pu and 241Am) emit low-energy (13-60keV) -rays. As a result, determination of whole body (or organ) counting calibration coefficients is hampered due to intensive absorption and scattering of radiation in the patient's body (organs).

To circumvent these obstacles, one could use mathematical simulation (particularly Monte Carlo Method (MCM) as almost the only valid calculation method for such a purpose) rather than measurement of reference phantoms. The multi-platform (MS Windows and UNIX) graphic user interface OEDIPE], French acronym corresponding to "tool for assessment of personalised internal dose" which has been developing at Institut de Radioprotection et de Surete Nucleaire (IRSN, France) is a very good example of what it could be done in this field. It has been specially designed for applications in internal dosimetry and whole body counting. To perform radiation transport calculations, the software OEDIPE creates automatically MCNP input files notably based on individual patient tomograms.

The potential of OEDIPE in the frame of IDEA project has been studied through two applications. The first is related to the measurement of high-energy emitters in whole body counting and the second is related to the measurement of actinides in the lung.

The application of voxel phantoms in whole body counting
The study was performed with first, the creation of the voxel phantoms of the physical IGOR phantom family (6 sizes) dedicated to Fission and Activation Products measurement and second, the validation of experimental results with simulations. Agreement is rather good between measurement and simulation for all energies and any type of phantom since an average difference of less than 15% is observed showing the ability of Oedipe to be used in WBC for further investigations.

The application in low energy monitoring
The strategy used was practically the same as applied in case of whole-body phantoms. The utility was firstly tested for low and medium energy actinide emitters on anthropomorphic Livermore phantoms, the mannequins generally used for in vivo counting, in order to compare the results of simulation and measurement. From these results, two kind of experiments were done: (i) the demonstration of the utility's abilities for the simulation of real facilities showing a good agreement between simulation and measurement for energies higher than 20keV with a difference less than 10 and about 20% at 17.51keV and (ii) the study of geometry uncertainties, such as different anthropomorphic phantoms or different source geometries, on in vivo calibration was investigated.

In the frame of the European project, the validity of the new software has been tested for low-energy -ray spectrometry of actinides and whole body counting when measuring plastic phantoms and its potentiality in various measurement situations. As a result, the interface proves to be useful for whole body counting calibration where the influence of a calibration phantom to the interpretation of the measured data has been studied. Moreover, the software enables taking into account individual patient's anatomy, which may result in up to two-fold and more correction factors for activity assessment.

Consequently, as a result of its flexibility in accommodating complex geometry, the method developed not only represents a diagnostic tool for in vivo measurement, but also opens up new possibilities such as the optimisation of detection systems, the study of contamination with mixed actinides and any other simulation using MCNP where complex geometry is derived from a set of superimposed images.

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Franck DIDIER, (Head of Unit)
Tel.: +33-1-58357874
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