Radiation exposure to human trachea from xenon-133 procedures

The general dosimetry of 133Xe for human studies is well documented, but the resultant radiation exposure to tracheal tissue is poorly known. This organ is of central relevance because the tracer is primarily eliminated through exhalation.

We report actual 133Xe concentrations in respiratory air during measurement of regional cerebral blood flow (rCBF), when the tracer is administered both by inhalation and intravenous injection. Data were collected from 102 patients, with equal gender representation and an age range of 18-82 yr. Most of the patients had subarachnoid hemorrhage or Alzheimer's disease or were normal control subjects. Average administered doses were 18 +/- 4 mCi by inhalation and 15 +/- 3 intravenously.

We found average respiratory concentrations of about 1.80 mCi/liter during a 1-min inhalation and 0.74 mCi/liter following intravenous injection of standard doses. These activities drop rapidly: average respiratory concentrations during the second minute are 0.70 mCi/liter for inhalation and 0.19 mCi/liter for intravenous injection and reach negligible levels thereafter. We calculate that the tracheal absorbed dose from 133Xe procedures is approximately 28 mrad following inhalation and about 11 mrad following intravenous injection. These values reflect the full 11-min exposure, but most of the activity is only present initially.

These values will agree with previous estimates and indicate an excellent safety margin.