Experimental and Monte Carlo assessment of activity pattern with voxel phantoms for 30 years old actinides wound contaminations

In vivo measurements have been performed with a devoted four Germanium detector system on two male patients presenting a 30 years old wound contamination by Americium and Plutonium isotopes. This paper presents the measurements and discusses their interpretation when only minimum hypothesises about the internal activity distribution are used. 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 phantoms construction and MC calculations were assisted by the OEDIPE software and the reliability of the modeling has been controlled by the comparison of the measured and simulated efficiencies for well known sources. Mainly based on measurements at the knee level the 241Am specific bone activity is found to be (0.27 ± 23%) Bq/g for the first patient, and (0.04 ± 20%) Bq/g for the second one. Using measurements at the thorax level no activity can be detected in the lungs. For the first patient the liver activity is found to be 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. For the second patient the liver activity is found to be (90 ± 20%) Bq and the activity of axillary lymph nodes (300 ± 20%) Bq, no activity can be detected in the lungs but a residual activity in thoracic airways lymph nodes can be suspected. (author)