A unique feature of the present cases was the appreciable differences tn (he latent periods
observed for legions on various parts of the body. These differences cannot be explitned
entirely on the basis of severity, since the severe foot legions develuped aller most other le-
sions. However, the severity might have been in part due tu the dependent position of (he toot
rather than greater radiation injury. Lesions on flexor surfaces in veneral preceded lesions
on extensor surfaces. The present data suggest that the latent period and radiation sensitivity
of various skin areas may differ. Previous work has shown that flexor surfaces with thinner
epidermis are in general more sensitive than extensor surfaces with thicker epit helium, !
The destructive and atrophic changes of the epidermis, disturbances in keratinization, and
atrophy of hair follicles are characteristic of histopathologic radiation injury of the skin.?!318-4!
Severe injury to the dermis and blood vegsels was not observed. The minimal dermal injury
with severe epidermal injury is in keeping with the low energy beta component present and the
marked decrease in depth dose over a distance of a few microns from the surface.
Hyperpigmentation of injured areas was a consistent finding in the Marshallese, the Japanese, and the American Negroes.
Pargmented Jesions were alao observed to a lesser extent in
the white Americans. Pigmentation of (his nature has not been described as a constant charac teristic of radiation damage to the skin.
There is no satisfactory explanation for the darker dusky-gray color (hat appeared in
some of the skin Jesions as healing progressed. The color changes may be due to alterations
wi local pygment production, vascular changes, or a thinning of the epidermis, rendering if
more translucent with resultant darker appearance of the pigment layer. Later biopsies may
explain this phenomenon.
,
There are features of the lesions described that appear unique, e.g., the absence of visible
multiphasic responses, the presence of early hyperpigmentation, the long latent periods, and
the severe epidermal) injury with minimal dermal injury. It is possible that differencea may in
purt be on a racial basis.* In addition, the marked difference in histologic response of the
epidermis and dermis in the present series is in marked contrast to the usual radiation response of the skin produced by high energy X- or beta-rays.
In Table 3.3 are listed the approximate minimal surface skin doses required to produce
recognizable epidermal injury in ar..mals. It is apparent from the table that beta'ray energy is
of considerable importance in determining the degree of injury. A number of assumptions, including knowledge of the beta ray spectrum from the fallout, would have to be madeif these
data were to be used to estimate biologically the beta dose received by the Marshallese. The
difference in dose between that required to produce threshold skin damage and that for per-
manent damage in pigs is 500 to 1000 rep.*°
{t 1s impossible to estimate the probability of development of radtation cancer at the site
of the healed lesions. The absence of scarring, telangiectasis, and extensive chronic vascular
lesions tends to improve the prognosis since the foregoing are usually observed tu precede the
development of radiation cancer.
A favorable prognosis 18 aigo suggested by the fotlowing evidence: an analysis of 1100
individuals exposed tu low vultage X-ray for dermatological conditions revealed nu evidence of
cancer induction 5 to 23 years after treatment. MacKee'® states that epitheliomata rarely
develup after a single dose of radiation to the skin. Lastly, the incidence of skin cancer in
Negrveg 18 one sixth to one ninth the incidence in Caucasians.**
If neoplasia can develup purely as the result of epidermal irradiation, the incidence of late
cancers may be enhanced since the dose of radiation and the visible gross and microscopic injury to the epidermis greatly exceeded that to the dermis. Since many children and young
adults were involved, the life expectancy of a large number of the exposed people will exceed
the long induction period for development of radiation cancer observed in radiologists. Long
* Reported clinical experience with radiation skin lesions i3 based predominantly on the
response of white-skinned people, whereas the type of legions ceacribed herein, with one clear
cut exception, were obscrved in Japanese, Marshallese (negroid), and American Negroes. The
exception was a dark brunette individual.
44