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dema, with much lower radiation doses than those required from inter-
nally administered radioiodine. After 2,000 rads of x rays to thyroid
the myxedema appears in about a year. With reduction of x ray dose
the time taken for the myxedema to develop in dogs increases ina
manner indicating a slower progression of the underlying mechanism
at lower doses. There is a possibility that radiation from external
sources, in addition to the internal radioiodine, may have contributed
to the thyroid changes in the children in question.
BUSTAD: That was my next point.
I think that 200 r or 300 r is
, not an insignificant arnount {rom the standpoint of thyroid damage.
These children probably received a considerably more effective dose
per rad from external gammato the thyroid than from 143! and there
is some substantiation for this from animal data. And if I can then
stretch a point and say, "Well it's five times more effective"'.....
UPTON:
gland?
BUSTAD:
to this.
.....because of dose rate or dose distribution within the
Yee, I think there are at least two things that contribute
In order to get the same equivalent rad to the thyroid from
p31 you have a much lower dose rate because it's extended over many
days.
With the total body radiation it waa a sudden thing over a matter
probably six or eight hours. In any case it was very acute. The other
thing is that a lot more than thyroid tissu* was affected following external gamma exposure. With the radioindine, however, the periphery
of the thyroid gland is probably receiving 25 percent of the dose at
the center of the gland while in the case of external irradiation the
entire thyroid gland is being uniformly irradiated as a.e the contiguous
structures, I think this too is important.
The other thing that is worthy of note is that in Dr. Hempleman's
studies (Reference 28), which I briefly discussed during our first
meeting, he noted a high incidence group of about 268 children who
were irradiated early in life anteriorly and posteriorly for total doses
of 200 to 600 R or more,
Of the 268, there were 20 that manifested
thyroid neoplasms. Half of these were cancers, It's interesting to
me to note that in your Marshallese group, Bob (Dr. Conard), the
children manifested no cancer, only thyroid adenomas (Reference 29).
This was algo the pattern in our sheep studies. We had one fibrogarcoma and one adenosarcoma and 30 or more adenomas, and this
pattern of response has characterized most of the followup studies
of the children who were exposed early in life to radioiodine. That