New Method Based on Monte Carlo Calculation and Voxelized Phantoms for Realistic Internal Dosimetry: Application to a Complex and Old Actinide Contamination

In vivo measurements are usually carried out under the hypothesis of a known activity distribution inside the body. The measurements and the interpretation of in vivo measurements performed with the minimum hypothesis about the activity distribution are presented and discussed. Measurements have been performed with a devoted four-germanium-detector system on a male subject presenting a 30-yr-old wound contamination by americium and plutonium isotopes. The measurements have been processed after the construction of voxelized phantoms of the measured body parts and Monte Carlo (MC) calculations of organ- and detector-specific counting efficiencies. The phantom construction and MC calculations were assisted by the OEDIPE software, and the reliability of the modeling has been controlled by a comparison of the measured and simulated efficiencies for point-source measurements and for the measurement of a Spitz anthropomorphic knee phantom. Mainly based on measurements at the knee level, the ²⁴¹Am specific bone activity was (0.27 ± 23%) Bq/g. Using measurements at the thorax level, no activity could be detected in the lungs; the liver activity was between 410 and 460 Bq. The activity of the axillary, thoracic airways and trunk lymph nodes depends on the retained hypothesis, but a reasonable assessment for the axillary lymph nodes is between 100 and 350 Bq.