were noted over the dose range from 100
to 900 rads.
The British data were obtained from follow-up stucies on about 15,000 patients, predominantly males of 14 years and older,
who were given radiotherapy for ankylosing
spondyiitis*® 3% 33; 73 cases of leukemia have
occurred am ng these patients. The number
or cases of leukemia expected in this study
population in the absenceofirradtiation has
been estimated to be iour or five.?? These patients received therapeutic doses of radiation;
therefore, “this study does not provide evidence on leukaemia incidence after doses be-
jow 500 rad.’** Other epidemiologic investigations have indicated that children with
leukemia have had greater exnosure to radio-
therapy than’ have comparison groups
and that children subjecied to therapeutic
irradiation, particularly to the thymic arca,
have a higher incidence of leukemia than
expected.” "3° In some reported sevies,
hovwever, children who received : eraneutic
irradiation, including’ irradiation of° the thy-
mus, did not showa significant incidence of
leuxemia.**9? Again, the history of therapeu-
tic radiation is not always a significan: finding in leukemic children.* 4? The <otal voi-
ume of tssue Irradiated (bone marrow} has
been suggested as a factor of importance.*®
Although increased irequency of deaths from
leukemia among American radiologists has
been reported,*?:#? the data do not contribute toward quantitative aspects of the
probiem.*> +
Several attempts have been made to determine the probability of leukemogenesis on
the basis of radiation dose.*% *4-42 The
conc.usions do not definitively answer the
question of the existence or nonexistence of a
threshold radiation cose for the development
or icukemia in man.** A cause and effeci
relationship, however, between high-dose
radiation exposure in man and increased
incidence of ieukemia must be accepred.*°
Cancer. Tne correlation between ionizing
and the occurrence of :malignan
ot
radiation
&
neopiasia other than leukemia has been th
object of intensive scientific inquiry since th
0
in the proximally exposed and 6 per million
in the cistally exposed cnildren.$ ’ * Straightline reiationships between irradiation doses
and ieukem!
incidence in the Japanese data
October 1965
publication of reports of increased carcino-
nesis in children who were irraciated in in-
fancy for thymic enlargemeni.* * Cancer of
the thyroid gland apnoears to be the most
frequent malignant tumor noted in these
studies.*"* *#” Eleven cases of thyroid canc.
developed in a group of 1,644 children given
x-ray therapy to the head, neck, or chest. in
the same pooulation, 0.12 case would have
been expected. Irraciation dosage in the il
allo
7
~
Cauaren ran
wed from 100 to 1,770 r in air.®
In another prospective stucy of 2,809 in-
fants wno had beeen therapeuticallyirraciated
for thymic erlargentent, 9 cases of thyroid
ancer were found 0.10 case expected, in
addition to 21 cases of thyrcic acenoma (GY
case expected). The 9 with unvroid cancer
had cumulative exnosures ran
io 1,092 rin air with a mean of 398 v7 Al
though the developmen: of “thyroid nodules”
has been ascribed to prior therapy with
1odine-131,*% °° only one case of thyroid
carcinoma has been reported amoz.z pacients
so treaied.*® #9 Varicus data suggest that the
formation of the nodules was more frequent
in children than in adults (33.3 per ce 4
compared to 0.84 per cent).*® Clinical
ob1
a
woke
ct
oy
oc
q>
Sutow and Conard
servations nave sadicared that the history or
antecedent therapeutic irradiation to the necs
area was signifAcantly very common (up to
- and adolescents win
80 per cent} in children
thyroid cancer.*% % in
n the ALCC survey in
japan, 21 instances r thyroid cancer were
found over a three-year period (1958-1 i)
among more than 19,0G0 persons in the
study sample.** Nineteen of the 21 occurred
in the exposed group. Two were under 13
years of age at time of exposure; 6, howeve-,
were under 21 years of age at exposure. Tenative exposure doses (T;sz), Computed on the
basis of exposure distance and shielding history of these cancer cases, ranged from 125
to 3,00 rads with the excedtion of a sing.c
patient whose T;:; dose was calcularec
.
have been 33 rads.°* It was concluded from
these findings thar thyroid carcinoma was
significantly more prevalent among survivors