Estimation of the Distribution of Thyroid Doses in a Population Exposed to I131 from Weapons Tests

Abstract

Management of the public health aspects of generalized environmental contamination by 1131 requires that estimates be made of the mean thyroid dose received by a given segment of the population. Some measure of the distribution of doses around the mean is also desirable.It is possible to estimate the absorbed dose to the thyroid gland by analysis of post-mortem material, by in viuo measurements of a sample of the exposed population, or by calculations based on environmental data. When the exposed population is so small that meaningful data can be obtained on a sample of manageable proportions, in vivo measurements are highly useful. However, when the exposed population is a substantial part of the country, as in the case of fallout associated with the testing of nuclear weapons, it is impractical to obtain reliable estimates of the distribution of thyroid dose because of difficulties of obtaining a representative sample and because of the logistic problems associated with this type of measurement.The problem of calculating the distribution of doses based upon knowledge of environmental factors is simplified by the fact that fresh cow's milk is known to be the principal route by which 1131 is absorbed. This paper discusses the mathematical relationships that determine the distribution of thyroid doses in the exposed population and discusses the feasibility of undertaking such calculations based on both existing data and data yet to be obtained.

Appendixes

“…13,14). [11][12][13][14][15][16][17][18][19][20][21][22] A sensitivity of 10nCi/1. of urine (corresponding to 14nCi/day) permits the detection of one Investigation Level 4 days after the event.…”

“…It is assumed that this iodine is absorbed into the blood (Refs. [17][18][19][20] although this is doubtful in the large intestine. The radiation exposure from Part 1 is obtained by integrating equation (9) with respect to time from zero to 50 years and is 0"011 ~Ci-days.…”

“…This question has been considered repeatedly in papers and reviews (Refs. [17][18][19][20][21]. In summary of the published facts it may be stated that the percentage uptake appears to be constant with age except for the first few days of fife, during which time it may be twice as great.…”