Gross distribution of 241Am in a man seven years after inhalation

The gross distribution of 241Am remaining in a man seven years after exposure to airborne americium particles has been determined by several techniques. Measurements were made of the radiation with NaI(Tl) crystals, one above and one below the supine subject at seven equally spaced points along the long axis. The patterns obtained indicated skeletal deposition in addition to material in the thorax. More detail was obtained from a longitudinal profile scan made at 10-cm intervals with a slit-collimated detector. A general labelling of the skeleton consistent with bone surface deposition was observed, together with a pronounced increased concentration in the thorax. A transverse profile scan was made at the point which had yielded the highest counting rate in the longitudinal scan. Unequivocal evidence for a lung burden was observed in the asymmmetry of this scan. The presence of the long-term lung burden was further confirmed by measurements made over the chest with a gas-filled proportional counter. The ratio of primary quanta in the 60-keV peak to those which had been forward scattered indicated that the radiation had passed through approximately 5 cm of soft-tissue equivalent absorber. Since estimates of the subject's chest wall thickness were only about 2.5 cm, the major part of the radiation was coming from deeper in the chest, below the level of the rib cage. Therefore the material in the chest was primarily in the lungs and not in the bones of the thoracic cage. The proportional counter also showed that there was little contamination in the liver and spleen. This was expected since the subject had undergone extensive chelation therapy with DTPA at another centre. The whole-body content of 241Am was estimated to be 1.00+-0.03 μCi, with about 25% of this amount in the lungs. Thus a sizable fraction of the material retained is still in the lungs after seven years. (author)