Harold L. Atkins
94
Table 6-2
Calculated Radiation Dose to the Thyroid From '*I (1 mCi in a 20-g Gland)
Initial Dose Rate (rads/day)
Author
Whole
Gland
Harperet al.5?
36.8
Gavron and Feige*!
78
Lewitus et al.**
Ben-Porath et al.**
MIRDt
88.8
Gillespie et al.*9
Reddy et al.*°
75
72
Colloid-Cell
Interface
170
457
63.6
151.2
77.8
Nucleus
46
112
Total Dose (rads)*
Whole
Gland
795
1620
32.4
1685
37.2
25.9
1918
Colloid-Cell
Interface
Nucleus
3672
9871
994
2419
3266
1680
804
559
1374
700
1555
*Assumes T% eff. of 115 days.
+Author’s calculation using MIRDtables for absorbed dose per unit cumulated activity.*°
Several clinical trials of '°I for hyperthyroidism were initiated in the hope
that late hypothyroidism could be substantially reduced (Table 6-3). These have
varied in the dose of '*1 used relative to the conventional'*'I dose and the results
have been mixed. At least two groups have discontinued their study because of
lack of improvement in results.
In Glasgow the initial trial used a dose in millicuries of '**] four times the usual
dose of '*4I. This resulted in a rapid reversal of the hyperthyroid state but with a
substantial percentage of ensuing hypothyroidism. With reduction in the amount
of '=] administered the incidence of hypothyroidism decreased, but with an increase tn persistent hyperthyroidism.®*
On the other hand, Israeli investigators have used fewer millicuries of '*1
than of '*'I, assuming a quality factor of 3 for the rad dose in the apical region of
the cell from the low-energy Auger electrons.® The relapse rate was high leading
to the use of increased doses andfinally to a combination of !*1 and "I in equal
millicurie amounts.®* With this combined therapyit was felt that a rapid response
by affecting hormonogenesis wasinitiated by **5I and that long-term effects were
maintained by the cell killing action of '"I. This combination led to the lowest
incidence of recurrence but without much effect on the incidence of
hypothyroidism.
A series of patients treated by Siemsen etal.®’ initially showed a low rate of
hypothyroidism but with a high rate of persistent hyperthyroidism. No further
patients are being addedto this study because of the conclusion that the results
were nobetter than with '*!I. The series of Werneretal.®* and that of Weidingeret
al.’ continue, and a recent study by Glanzmann and Horst” shows promising
results.
In this last study there was no hypothyroidism at 18 to 24 months and 18
percent persistent hyperthyroidism. Of those patients with persistent or relapse of
thyrotoxicosis, more than 30 percent had T; thyrotoxicosis.
Another small series of patients was treated withI by Gimlette and
Hoschl.”! The dose of !41 was identical to the dose of }7I used in a control group.