Estimates of radiation absorbed doses from radioxenons in lung imaging. [/sup 129m/Xe and /sup 131m/Xe are contaminants]

The absorbed-dose estimate is given in rads per millicurie of administered activity. This was obtained for each target organ by considering the lungs and total body as source organs, the former consisting of Compartments 1 and 2, and the latter of 3, 4, and 5. In each case the component compartments are regarded as being coextensive. Tissues with high fat content concentrate xenon more than do the other tissues. As a working hypothesis we may assume that Compartment 5, with the slowest turnover rate constant, represents fatty tissues. The measured half-life for washout from this compartment averages 10.5 hr. Therefore, during buildup in the studies under discussion, only a minimal amount of radioxenon enters into fatty tissue. Because of unequal blood perfusion rates, the distribution of xenon among the fatty tissues will not be uniform, and a somewhat higher ratio will be attained in organs such as the brain, adrenals, and gonads; these having relatively high blood perfusion rates. The contribution from the 5th compartment to the total-body radiation dose from Xe-127 is about 28%. About 55% of the total-body radiation dose is from the activity in the lungs, and this will not be greatly affected by changes in localmore » tissue xenon concentration ratios. The listed absorbed dose estimates for the contaminants, Xe-129m and Xe-131m, must be multiplied by appropriate factors depending on the fraction of the contaminant present at the time of administration of Xe-127. Despite different assumptions, there is satisfactory agreement between previously published absorbed-dose estimates and those of this report.« less