Biological analysis and dosimetry for /sup 15/O-labeled O/sub 2/, CO/sub 2/, and CO gases administered continuously by inhalation

Estimates of radiation absorbed dose have been determined for the steady-state distribution of oxygen-15 (T1/2 . 122 sec) from inhalation of molecular oxygen, /sup 15/O/sub 2/; carbon dioxide, C/sup 15/O/sub 2/; and carbon monoxide, C/sup 15/O. Biodistribution data for /sup 15/O-labeled water, produced by the metabolism of oxygen and from CO/sub 2/ by pulmonary carbonic anhydrase, were used. Lung gas and intravascular activities are also included. The total oxygen utilized was taken to be 14.4 l/hr. Seventeen tissues were included as source organs. The radiation dose is directly proportional to the duration of inhalation. Air containing a constant level of /sup 15/O is provided in excess of need to the patient, who breathes under his own control. The lung, which is known to be a particularly radiosensitive tissue, appears to be the dose-limiting or critical tissue. The radiation dose estimates for lung, based upon 1 hr of breathing air with an activity concentration of 1 mCi/l, are 3.6, 1.2, and 2.8 rads, respectively, for /sub 15/O/sub 2/, C/sub 15/O/sub 2/, and C/sub 15/O.