Number +
HIGH DOSES
Somatic effects that result from substantial
doses of radiation have been well docu-
mented and the causal relationship of early
effects to the fact of exposure has been fairly
clearly established. The present knowiedge
regarding the late effects on humans which
occur months and yearsafter the exposure is
based on meager data from acute exposures,
from epidemiologic investigations, and from
occupational and medical exposures.?*: 76
These late effecis are nonspecific and cannot
be differentiated from naturally occurring
disease; only the incidence of the disease is
increased.’* Tne general pattern of somatic
effects following irradiation varies with several factors which include the quality of
radiation, absorbed dose, and raie and
homogeneity of exposure (spatial distribution),
Acute effects. The median acute Iethal
dose (LD5,j in man ior short-term total
body radiation is not precisely known but is
estimated to be somewhere between 300 and
500 rads.** ?* Doses over 2,000 rads are fatal
within a few hours, producing rapid clinical
deterioration in which neurological symptoms are strining. Between 300 ana 2,000
rads, effects are characterized by severe
gastrointestinal disturbances; death occurs
within a week. Arter an exposure to 100 to
500 rads, less serious gastrointestinal symptoms precominate in the early clinical pattern, Following subsidence of the gastrointestinal symptoms, the eifects of injury to
the hematopoictic tissue (infections, anemia,
bleeding} may become evident in abour 3
weeks.?" Clinical syndromes of acute radiation injury have been descrived in. detail
in a numberof pubiications.74*#
The relative sensitivity of children com-
pared with adults to high doses of radiation
is not precisely known. “In assessing susceptibiliuics various end points can be used;
the apparent radio-sensitivity of a tissue or
organ depends on the method of observation.
Sensitivity depends on age at the time of
exposure, children being more susceptible
than adults."%* Marshallese children irradi-
>
659
ated with 175 rads of whole body gamma
rays snowed a slightly greater degrce of
nausea and vomiting and greater depression
of leukocytes than did the adults.** ** However, the dose may have been greater in
these children due to their shorter stature
(nearer the ground source) and smaller
bodies. The skin of children is known to
be more sensitive to radiation than that of
adults.*” The Marshallese children exposed
to fallout also developed more widespread
“beta burns” of the skin and epilation than
did the adults. This greater sensitivity may
be related to the thinner skin of the children,*°
Late effects. In considering the possible
late effects of radiation, it should be borne
in mind that children have a greater chance
of developing some of the late effects since
their lonyer Hie span would permit effects
with prolonged latent peviods io become
manifest,
Leukemia. The occurrence of leukemia as
the result of exposure to ionizing radiation
has been established in studies of atomic
bomb survivors in Japan®,% 27° #9 and of
therapeutically irradiated ankvlosing sponGyvitis patients in England*® 31 In the
Avomic Bomb Casualty Commission (AB
CC) study, calculations based on 82 cases of
confirmed leukemia of ail types occurring
from 1947 through 1958 among the proxinally exposed (within 1,500 meters of the
wypocenter) survivors demonstrated that ihe
highest calculated annual raie of 673 per
milion was in the age group 0 chrough 9
years; the calculated over-all incidence was
455 per million for all age groups combined.
During the same period of time, the leukemia
rates among the distally exposed (1,300 to
10,000 meters from the hypocenter} survivors, calculated on the basis of 67 confirmed
cases, were 26 per million in the 0 through
9 year ave group and 35 per inillion for al
ages combined.» * The expected incidence of
leukemia of all types for all ages in Japan
was 20 to 30 per million per year? When
acute Ivmphocvtic leukemia was considered
separately, the calculated annual rates in tie
O through 9 age group were 269 per million
5
SOMATIC EFFECTS OF
Effects of tontzing radiation
me
Volume 67)