Application of Monte Carlo calculations to the evaluation of uncertainties in the assessment of the retention of radioelements in the lung
Workshop on Internal Dosimetry of Radionuclides - Occupational, Public and Medical Exposure - 9-12 September 2002 - New College, Oxford, United Kingdom
D. Franck (1), N. Borissov (1), L. de Carlan (1), JL Genicot (2) and G. Etherington (3)
(1) IRSN (Institut de Radioprotection et de Sûreté Nucléaire), Département de Protection de la santé de l'Homme et de Dosimétrie, BP17, 92262 Fontenay-aux-Roses Cedex, France
(2) Belgian Nuclear Research Center (SCK•CEN), Boeretang 200 - B-2400 Mol, Belgium
(3) National Radiological Protection Board, - National Radiological Protection Board (NRPB), OX11 0RQ, Chilton Didcot , United Kingdom
Although great efforts have been made to improve the physical phantoms that are used to calibrate in vivo measurement systems, these phantoms represent a single average counting geometry and usually contain a uniform distribution of the radionuclide within the tissue substitute. Because in reality the deposition is heterogeneous in the subject, this can result in large uncertainties in the assessed activity. In consequence, significant corrections may need to 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 for in vivo measurements of low energy photon emitting radionuclides (such as actinides) deposited in the lung. Thus, it was desirable to develop a method for calibrating in vivo measurement systems that is more sensitive to these types of variability. Previous work has 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 (CT) and MRI. New procedures are being developed to take advantage of recent progress in image-processing codes. They allow after scanning the direct and fast reconstruction of a realistic voxel phantom, coupling of voxels with the same density and chemical consistency into logical cells and conversion into computer files to be used on line for MCNP4b calculations. First results of calculations and comparison with the experimental data are presented and discussed in this paper.