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To improve calibration methods of in vivo counting, our laboratory has developed a computer tool to model internal contamination and assess in vivo activity and corresponding organ absorbed doses. The aim of the recent work was to define a more realistic source based on biokinetic models. The influence of the biokinetic parameters on the in vivo counting was studied through the simulation of an acute inhalation intake of (241)Am. The tissue distribution of activity predicted by the biokinetic model was visualized. Two equivalent methods for determination of the efficiency related to the total activity distributed in the body were used. The comparison between the efficiency taking the biokinetics into account and the classically estimated efficiency quantifies the influence of the activity distribution in the body and provides conversion factors for correcting the classical efficiency to account for biokinetics.

The activity and local dose following a right index finger wound contamination by activation products are assessed. Measurements with a high purity germanium detector and a four positions measurement protocol enabled a better localization of the contaminant source. From the source location and detector calibration, the remaining wound activity and local absorbed dose were deduced. An analytical model, based on a two dimensional simplification of the problem, is presented. It is shown to provide a fast and quite accurate activity assessment when the contaminants are described as a point source. The contaminants' location and activity were then more accurately assessed using Monte Carlo calculations based on the OEDIPE software and a voxelized phantom of the index finger. Describing the contaminant mixture as a point source resulted in an agreement of experimental and computed data around 6% for most of the radionuclides. The total activity, due to 11 radionuclides, was estimated to be (9.5 +/- 0.4) kBq at measurement day. Since the point source is found to be less than 1 mm under the skin, the equivalent skin dose is calculated and found to be around 680 mSv in the first year after the contamination, and this value decreases to 250 mSv in the second year. The relevance of equivalent skin dose as an estimate of the sanitary risk is discussed, and it is concluded that for this case it gives the upper end estimate of the risk.

Although great efforts have been made to improve the physical phantoms used to calibrate in vivo measurement systems, these phantoms represent a single average counting geometry and usually contain a uniform distribution of the radionuclide over the tissue substitute. As a matter of fact, significant corrections must be made to phantom-based calibration factors in order to obtain absolute calibration efficiencies applicable to a given individual. The importance of these corrections is particularly crucial when considering in vivo measurements of low energy photons emitted by radionuclides deposited in the lung such as actinides. Thus, it was desirable to develop a method for calibrating in vivo measurement systems that is more sensitive to these types of variability. Previous works have demonstrated the possibility of such a calibration using the Monte Carlo technique. Our research programme extended such investigations to the reconstruction of numerical anthropomorphic phantoms based on personal physiological data obtained by computed tomography. New procedures based on a new graphical user interface (GUI) for development of computational phantoms for Monte Carlo calculations and data analysis are being developed to take advantage of recent progress in image-processing codes. This paper presents the principal features of this new GUI. Results of calculations and comparison with experimental data are also presented and discussed in this work.

Although great efforts have been made to improve the physical anthropomorphic phantoms used to calibrate in vivo measurement systems, each of these phantoms represents a single average counting geometry and usually contains a uniform distribution of a radionuclide in the tissue substitute. As a matter of fact, significant corrections must be made to phantom-based calibration factors in order to obtain absolute calibration efficiencies applicable to a given individual. The OEDIPE software has been developed at the Institute for Radiological Protection and Nuclear Safety. It allows the direct and fast construction of a voxel phantom from medical images with a realistic distribution of activity between organs and its conversion into computer files to be used online for Monte Carlo calculations. OEDIPE allows determining and visualizing the variation of activity retention in the segmented organs of the phantom and running MCNPX with these calculated source-organs at different times after intake. The influence of the biokinetics of radionuclides on the in vivo measurement as well as the uncertainty on the estimated activity is quantified by comparing the numerical calibration coefficients obtained by considering realistic and dynamic biokinetic distributions of activity with the counting efficiency commonly obtained from simple, homogeneous, and static activity distributions in organs or in the whole body. As an application, the effect of long-term retention tissues was studied through a case of inhalation of an insoluble compound where the thoracic lymph nodes make a significant contribution to the lung counting efficiency. Future work will concern contamination through other routes of intake, such as a wound, and mixtures of radionuclides. [ABSTRACT FROM AUTHOR]