followed by acute radiation dermatitis manifested by blister formation,
dermal hypoplasia, edema, and permanent depilation. The normal skin
reappears in 2 to 3 months.
The above effects depend on the dose, dose rate, LET of the radiation,
and the duration of exposure, and vary from individual to individual and
with the location in the same individual. Although sex is not a factor in skin
reaction, age is an important factor, with the skin of younger people being
more sensitive.
A low-level chronic exposure of radiation on the skin causes atrophy,
hyperplasia, and hyperkeratosis. In addition, ulceration and deep fibrosis
may result from such exposures. In rare instances, skin cancer, mainly squa-
mous cell carcinoma, may develop.
Radiation Damage to Reproductive Organs
Extremely deleterious effects are expected from radiation exposure to the
gonads, because of their high radiosensitivity. In males, spermatogonia are
most radiosensitive, and spermatozoa and spermatids are radioresistant,
whereas in females, the ovarian follicles are most radiosensitive. The radi-
ation effects vary with the dose, dose rate, sex, and age.
Sterility is the important radiation effect that warrants special attention.
In males, temporary sterility can be induced with a dose as low as
15 rad (15 cGy), whereas permanent sterility is reported with an acute dose
of 500 to 600 rad (500 to 600 cGy) (Prasad, 1995). Male sterility is evident
by a reduced sperm count and low motility. In females, permanent sterility
occurs with 320 to 625 rad (320 to 625 cGy), which is manifested by the
damage to the ovarian follicles. If the dose is lower, then the follicles may
recover in 5 to 6 months. Relatively larger doses are needed in younger
women than in older women.
Nonspecific Life-Shortening
Studies have shown that exposure to ionizing radiations results in the short-
ening of the life span of mice (Rotblat and Lindop, 1961). For acute total
body exposure, the life span of mice, rats, and dogs is reduced by about 5%
per gray (UNSCEAR, 1982). The irradiated group looks much older than
the control group, and radiation effects are similar to those of normal aging,
e.g., an increase in connective tissue and a decrease in parenchymal cells.
During the period 1945–1955, American radiologists were found to have a
shorter life-span than other medical professionals. But the issue of life-
shortening by radiation is controversial, because in some cases it has been
found that life span is rather lengthened by irradiation at low doses. Such
observations have led to the concept of hormesis, which states that low
doses of radiation are beneficial to health and prolong the life span. It is
postulated that hormesis is secondary to an enhanced immune responsive-
ness due to radiation at low doses.
254 15. Radiation Biology