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-3preceding few days or weeks. Iodine not absorbed by the thyroid]will be
rapidly excreted, primarily in the urine. Thus, in a short timefafter a
Single intake, the gland will contain the highest concentration qf the
iodine remaining in the body. Because of its great avidity for qadioiodine the thyroid will receive the largest radiation dose, part {cularly
if the form is fodine-131.
The radiation dose delivered to other tissues will be, at mdst, a few
percent of that received by the thyroid gland. A concentration
1 pe
of iodine-131 per gram of thyroid tissue will produce_a time-integrated
dose of about 113 rads,° ranging from 90 to 130 rads.’
About 10
of this dose will be received in the first 24 hours, probably ovek
in the first 2 days,
percent
25 percent
When the thyroid is included in the beam from an external raBiation
source, such as an X-ray tube, a considerable amount of surroundi
g tissue
will necessarily receive doses equal to or even greater than that received
by the gland itself.
Differences in growth rate and histology of the thyroid from birth
through early childhood have led some to believe that the infant | hyroid
is more vulnerable than that of the adult to injury from ionizing radiation. In addition to differences in size and proportion of prolii erating
cells of the thyroid in infants, children, and adults, there may e sig-
nificant alterations in absorption, metabolic turnover, and cell
ensiti-
vity with advancing age, Any of these factors might affect the a ount of
biclogical damage resulting from a given radiation dose, Neither the
relative importance nor the aggregate effect of these variables iq known,
HUMAN EXPERIENCES
1.
Direct Effects of Iodine-131
It has been pointed out that iodine-131 entering the body is promptly
The
direct radioblological effects are thus confined to the gland itsefif. The
principal effects, which have been observed only after high doses £
radioactive iodine, include a decrease in the metabolic activity o the
gland, and at still higher doses, an atrophy of epithelial cells, nd the
and selectively concentrated in the thyroid gland, or is excreted.
appearance of numbers of atypical cells.
These changes in functio
Structure are seen only after doses of thousands of rads.
and
Thyroid cancer
is an uncommon result, described with certainty to date only in an Imals,
SReport of the Intemational Commission on Radiological Units and
Measurements (ICRU), 1959. National Bureau of Standards Handbook 78,
January 16, 1961, Washington, D. C.
’ Silver S.:
Radioactive Isotopes in Medicine and Biology.
Lea and Febiger, Philadelphia, 2nd ed., 1962, page 117.
Medicife.
DOE ARCHIVES
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