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Table 1.—Thyroidal Radiation Dose Estimates and Thyroid Nocularity,
Exposed and Control Marshallese Population, 1978

sured using commercial kits.

Prospective Studies

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1 to 6 pU/mL. Antithyroid microsome and
antithyroglobulin antibodies were mea-

Plasma T., TBGI, and TSH levels were

evaluated regularly in persons who had
had thyroid surgery and who werereceiv-

ing levothyroxine sodium replacement
therapy. In persons ‘not operated on, pro-

phylactic levothyroxine sodium replacement was discontioued for a period of two

to four months, and baseline thyroid function studies, a thyrotrophin-releasing hormone (TRH, protirelin) stimulation test

(500 yg of protirelin intravenously {TV}

followed by a plasma TSH measurement
20 minutes later), and, in some persons, a
TSH stimulation test (10 units of bovine

thyrotrophin given intramuscularly [131]
followed by a plasma T, measurement 24

hours fater) were performed.

Thyroid Dasimetry
Rongelap and Ailingnae are about 100
nautical miles east of the detonation site
on Bikini, and fallout began on these two’
islands four to six hours after the explosion. Utirik is 175 miles further east, and
the fallout appeared there 22 hours after
the detonation. The Marshallese were evacuated from these three islands about 48

hours after the fallout first appeared. The
_ dose to the thyroid of the Rongelap people
was estimated from the I in a pooled
“nrine sample collected 15 days after the

exposure.” The amount of "I in the thy-

roid of these subjects on the first day of

"fallout was estimated to be 11.2 wCi (5.6 to

22.4 pCi), assuming that 0.1% (range,
0.05% to 0.2%) of the maximum thyrcidal

Iwas excreted in the-urine on the 15th
day.” The quantities of shorter-lived
iodine isotopes ("I half-life [t], 25

hours; '"I t#, 21 hours; and '"I th, 6.7
hours), which are produced in the initial

fission process, could not be measured. The

dose to the thyroid from these isotopes
was calculated to be as much as three

times that received from '"I.”
The thyroid dose to the Rongelap adult
{including external + radiation) was esti-

mated to be 335 rad (220 to 450 rad) (Table

1). Because of the smaller size of the
_ thyroid gland in children, the dose due to a
given quantity of thyroid radioiodine was

larger than in adults.” A 3-year-old child

was thought to have received a thyroid
dose of 700 to 1,400 rad, and a l-year-old,
2,000 or more rad. In addition to the

variables of gland size, and the prevalence
of short-lived isotopes of iodine, a major
uncertainty is in the quantity of radicac-

tive jodine ingested by different individu-

als from contaminated food and water
during the two days before their evacuation. All subjects received total-body irra-

1572

Age at

Exposure,
ye (7954)

n

<10
" 10-13
>18

.

;

7

. 22(3)"
12
33

_ 390-2, 100
" 935-810
353

Ailingnae (whole-body + dase, 69 rad)

<10

ap. 10-18

'>18

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Unexposed
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Malignant Thyroid Nodules

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237

190

135 |

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17
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.

275-450

.. tf

Uticik (whole-body + dose, 14 rad)

“10
“4018
_ >a

Surgery for Benign or

Dose, Rad

Rongelap (whole-body + dose, 175 rad}

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“Numbers in parentheses indicate persons exposed in utero.

diation from external sources that ranged
from 14 rad on Utirik to 175 rad on
Rongelap (Table 1). These estimates of +

Table 2.—Ptasma TSH Concantratians
in the Marshallese Population*

exposure have been thought to be reasonably accurate, since the observed hemato-

TSH.

RESULTS
Normal Values for Thyroid Function
Tests in the Marshallese Population

The plasma TSH concentration in
the control Marshallese population is

presented in Table 2. In 115 unex-

posed persons who were clinically
euthyroid, 11 subjects had a plasma
TSH concentration greater than 3
pU/mL. Only one of these was greater

than 6 pU/mL. This person was a
59-year-old woman (subject No. 982)

whose plasma TSH concentrations
over the past five years have ranged
between 6 and 7 «U/mL, and whose

most recent plasma 7, level was 6.4
ppe/aL; TBGI, 0.76 units; and FTI 4.9

units. Antimicrosomal and antithyroglobulin antibodies were not detected.
Evaluation of samples obtained from
99 Utirik subjects exposed to low
levels of radiation showed that a
similar fraction (12%) had plasma
TSH concentrations in excess of 3

pU/mL, but none was greater than 6
nU/mL. On the basis of these data, a
value of 6 nhU/mL or greater was
considered abnormal in the Marshallese population. In 12 unexposed,
euthyroid Marshallese, protirelin infusion studies were performed. The

plasma TSH 20 minutes after IV

TSH

Level

logic depression in the Rongelap people

was in general agreement with what
would have been predicted.”

JAMA, March 19, 1982—Vol 247, No. 11

SO; fabs

.

No, of Subjects Having

Estimated Thyraid

Level

fm >SpU/smb Ss all/mt
Contro!
unexposed 115

Utirik

exposed

99

ti

*

12

.

1

‘

o

"Samples obtained between 1975 and 1979.

' TSH indicates thyrotrophin (thyroid-stimulating
hormone).

infusion of 500 yg of protirelin was
10.824.7 pU/mL (SD) higher than
the basal level. Ten euthyroid unexposed Marshallese were given 10 units

of thyrotrophin IM and their plasma
T. levels were measured 24 hours

later. The mean initial plasma T,
concentration in this group of ten
subjects was 6.0+1.7 pe/dL, and the
mean T, increment after introduction
of thyrotrophin was 4.2+£13 pg/dL.
Thyroid Function After
Thyroid Surgery

In the last column of Table 1 are
shown the numbers of subjects who

have had thyroid surgery (usually

subtotal thyroidectomy) for benign or

malignant thyroid nodules. During

the period 1972 to 1974, plasma TSH
concentration was greater than 6 »U/

mL (range, 6.2 to 460 w«U/mL)in 11 of
20 Rongelap persons who had surgery

despite the prescribed levothyroxine
sodium replacement. The number of

subjects in whom the residual thyroid '
function was inadequate was higher
than expected. This suggested that

Hypothyroidism and Fallout Exposure—-Larsen et al

Select target paragraph3