Production of monodisperse labelled aerosols for studies of pulmonary deposition and clearance in man

Quantitative data on the kinetics of clearance from the alveolar lung in man of insoluble particles are required in the evaluation of doses incurred when radioactive materials are inhaled. Techniques are being developed for producing monodisperse, insoluble particles labelled with γ-emitting radionuclides, and for their inhalation by human volunteers. Clearance will then be followed for a year by counting γ-rays using the scanning bed counter in the NRPB low background laboratory. Two aspects of clearance will be specially investigated, the effect of particle size and the extent of inter-subject variation. To determine these, it is proposed that twelve volunteers will inhale an aerosol consisting of particles of two distinct sizes (1μm and 5μm) labelled with different γ-ray emitters. Fused montmorillonite clay has been chosen to be the aerosol vector with strontium-85 (half-lie 65 days, photon energy 514 keV) and yttrium-88 (half-life 106 days, photon energies 898 and 1836 keV) the preferred γ-labels for the long-term lung clearance studies. Studies of the deposition and early clearance of particles in the respiratory tract, and tests on the equipment used for preparing and administering the aerosols require monodisperse particles labelled with a short-lived γ-emitter. Gallium-67 was chosen as it decays by electron capture with a half-life of 78 hours. The production of gallium-67 labelled montmorillonite clay, and the generation of monodisperse fused clay particles, are described. Apparatus is proposed for the administration of aerosol to volunteers. (U.K.)