“Volume 6)
Effects of ionizing radiation
Number +
tion of elements of the radium and thorium
series, of potassium-+0 and of carbon-14, provides radiation exposure from internal sources
in dose rates estimated to be 126 mrem per
year to the gonads, 130 mrem peryearto the
cells lining bone surfaces, and 122 mrem per
year to the hematopoietic tissues.
Medical diagnostic radiology constitutes
another source of inevitable low-level irradiation, the magnitude of which has been the
subject of recent inquiry.°% ° 9? The annual
genetically significant dose received by an
individual in the United States from diagnostic roentgenologic procedures has been
estimated to be 50 + 25 mrem minimum and
140 + 100 mrem probable.'* Although estimates of bone marrow dose are based on
sparse data and assumptions, the UNSCEAR
in two reports has suggested that the estimate of the population per capita dose
“might be of the order of 50 to 100 mrem/
y.’"'§ The radiation exposure from radio-
isotopes in pediatric patients for a numberof
diagnostic tests has also been calculated.*°
Adequate information on effects of low
doses in both man and experimental animals
is lacking. In 1959, Brues®** commented that
the subject of effects of low-level irradiation
concerned “hazards which, if they exist, cannot possibly be demonstrated to exist because
they are relatively so small.’’ Upton,®® in re-
viewing radiation carcinogenesis, stated that
663
was significantly increased by pelvic irradiation of the mother during the child’s
intrauterine phase.’ These findings were supported by data from several other studies.
3, 33, 97
MacMahon? has reported the results of
a study of 734,243 children born in and discharged alive from 37 large maternity hospitals in the northeastern part of the United
States from 1947 through 1954. For each of
three categories, leukemia, neoplasms of the
central nervous system, and other neoplasms,
the cancer rate was found to be “about 40
percent higher in the X-rayed than in the
unX-rayed members of the study population. The excess cancer mortality in the
X-rayed group was most marked at ages 5
through 7 years, at which time the relative
risk was 2.0. The excess risk apparently was
exhausted by age 8.” MacMahon hasestimated that the probability of death from
leukemia for white children in the United
States up to the age of 10 years will be
increased from 46 per 100,000 children to
62 per 100,000 children by prenatal irradiation.*”
In
a_
prospective
approach,®*
43,742
women who between 1945 and 1956 re-
ceived pelvic irradiation during pregnancy
were identified from the records of selected
hospitals (Edinburgh and London) and the
subsequent deaths from leukemia of the chil-
“existing data... are not adequate to permit confident estimation of the risks of small
increases in background radiation.”
Somatic effects. The report by Stewart
dren of these pregnancies were then investi-
diation of the pregnant mother wasassociated
with subsequent development of leukemia
and other malignant neoplasms in the child
who was exposed in utero triggered a number of similar epidemiologic studies. In sub-
indicated that ‘there was no evidence of any
disproportionate occurrence of leukaemia
among the children who had been most
and associates*® that diagnostic pelvic irra-
sequent communications, the original con-
clusions were confirmed and amplified.? ?
The study attempted to trace all children
in England and Wales who had died of
leukemia (792 cases) or other cancer (902
cases) before the tenth birthday during
1953-1955. It was concluded that the risk of
subsequent malignant changes in the child
gated. Court-Brown, Doll, and Hill,°* in this
study, found 9 instances of leukemia among
39,166 liveborn children when 10.5 was the
estimated expected number. The study also
heavily irradiated nor among the children
whohad beenirradiated early in intrauterine
life.” Data not in accord with those of
Stewart and of MacMahon have also been
reported from several other studies.** *°
Although the exposure dose cannot be
precisely determined in these studies,‘” the
reported association between prenatal pelvic
irradiation at diagnostic dose levels and increased leukemogenesis (and carcinogenesis)