Evaluation of uncertainties in estimates of fetal doses from 59Fe kinetic studies at Vanderbilt University

In a 1997 paper, Stabin et al, published estimates of the fetal radiation doses for women who received oral administrations of Fe-59 at Vanderbilt University in the 1940's, These authors concluded that there was "considerable uncertainty... In the amount of radioactive material administered to these subjects." In an effort to quantify this uncertainty, the underlying factors in the input data used in the Stabin et al, dose estimates have been examined in detail. Such factors include (a) an absence of detailed information on, and discrepancies in, the amounts of Fe-59 reported to have been administered; (b) the probability that the radioactive iron included Fe-55 as well as Fe-59; (c) uncertainties as to the period of time that elapsed between the administration of the radioiron and the taking of the maternal blood samples, and the accompanying impacts of radioactive decay; (d) possible losses of Fe-59 in the procedures used in preparing the blood samples; and (e) questions as to the reported efficiency of the counting equipment. Our principal conclusion is that, due to the significant uncertainties and the lack of key information, it is not possible to estimate the doses accurately. An ancillary conclusion, however, is that the doses were probably significantly higher than previously estimated. This latter possibility should be carefully considered by any investigators who subsequently seek to use these estimates to quantify the relationship between the doses to the fetus and the resulting health effects.