years after irradiation when 62 percent of them were stil] alive.
Had the
animals been allowed to live tonger, the production of tumors may have changed,
and the relative effectiveness of the two radiations may have been shown to he
different.
Differences in effectiveness in the production of thyroid gland effects by
various fodine isotopes have also been observed.
In studies of mice whose
‘thyroids were irradiated with 1331, 1321, or x-ray (Walinder et al., 1972),
X-irradiation and 132) (physical half-life = 2.2 hours) resulted in similar
effects that were grater than those fran 131,
In rats, using the inhibition
of goitrogenesis to canpare the effectiveness of 1311 and 1321, 1311 was
shown to be only 1/9 as effective as 1321 (Book et al., 1980).
Klassovskij
et al. (1971), who compared the thyroidal ef fects of 1313 with mixtures of
V30y, 1327, and 1331 (physical half-life = 2) hours) in rats, concluded
that the histologic effects of }311 were only 1/10 to 1/25 times as pronounced
as those fran the radfofodine mixture.
Studies canparing 1251 (physical half.
life = 60 days) and 131 indicate that up to 20 times more rads are required
fron 1251 than fran 1311 for the same suppression of tracer uptake or
inhibition of goitrogenesis (Gross et al., 1967; Grieg et al., 1970; Vickery and
Williams, 1971).
Hence, it can be concluded that these radiations indeed have differences in
their biologic effectiveness.
The differences, apparent between x-{frradiation
and 1, and among radiolodines with different half-lives and emissions, can
be considered to be related to the dose rate and the dose distribution of the
irradfations.
X-irradiation {s given at high dose rates and results in unifors
Irradiation of the thyroid.
lodtne-132, a short-lived radiatodine, frraviates
at high dose rates, and since tts emissions are fairly energetic, there is fair:
ly unfform irradiation.
flodine-13), with tts lomer half-life (rradiates at a