136.
In 1970 Eyring and Stover |E1] examined the life-span-shortening from
internal irradiation by 239 py and 226p4 reported for the beagle dog experi-
ments at the University of Utah [M18, S2hk, J1] making use of the steady-state
theory of mutation rates {S15, S551].
They fitted cumulative survival curves
as a function of the average skeletal dose accumulated by groups of dogs injected when young adults with various doses.
There was a high correlation be-
tween the mean survival time and tumour induction with the average skeletal
dose.
The log of the dose was proportional to the 50 per cent survival time
and the experimental data followed two quite unrelated slopes at low and at
high doses of injected 22650.
In the case of 239 Pu, on the contrary, the 50
per cent survival times followed a linear function of dose at the low doses.
This difference was taken to show that although both nuclides were effective
in inducing osteosarcoma, 22625 acted by inducing specific changes in one or
more compartments, while
239 Pu induced small changes which appeared to be ad-
jJuvants to the changes occurring through the aging process.
137.
The analysis of life-shortening was also extended to 228,,, 228, and
90... in subsequent publications
[S25, S26].
When the precentage of osteo-
sarcoma induction was plotted against the percentage of the life-shortening
produced by each dose level of each nuclide, a life-shortening of 60 per cent
was obtained when the tumour incidence reached 100 per cent.
At high dose
levels the degree of life-shortening was similar for all five nuclides but
this similarity was not maintained at the lower dose levels.
In the case of
2395, the incidence of osteosarcoma greatly exceeded the control incidence
even at the lowest dose level where no life-shortening relative to controls
was apparent.
In the case of 2262, progressive life-shortening was seen at
skeletal doses in excess of 2120 rad, where the occurrence of osteosarcoma was
between 92 and 100 per cent but practically no life-shortening was found at
skeletal doses between about 370 and 950 rad, although sarcoma incidence in
these groups was between 10 - 20 per cent and 42 per cent, respectively.
138.
From an analysis of data on yong beagles injected with single intra-
venous doses of 22a NO og 24 a, 2385. 228on 2288, 226n0 and 90 Sr Mays
and Dougherty [M18] concluded that all or virtually all of the life-~shortening effect observed at medium and at low doses of the nuclides is attributable
to radiation-induced bone sarcoma.
Thus, the thesis that the induction of
neoplasia is responsible for all of the life-shortening observed in the lowdose range of the experiments available is confirmed also in the case of a
medium size mammal injected with a variety of bone-seeking radionuclides.