to radiocarcinogenesis than older persons. Based on a relative-risk linear
quadratic dose response model, the BEIR V Committee (1990) predicts a
risk of excess lifetime leukemia cancer mortality of 10 in 10,000 (0.1%) with
an exposure of 10 rad (10 cGy). The BEIR VII (2005) estimate of this value
is 1 to 2.6 per 10,000 person years per Gy (1 to 2.6 per 100 person years per
rem). Leukemia appears in as early as 2 to 3 years after the exposure, with
an average latent period of 5 to 10 years.
Breast Cancer
The annual incidence of breast cancer in women in the United States is 1
in 11, with a high mortality rate. Several factors—age, estrogen level, heredi-
ty, demographics, race, number of children given birth to, and breastfeed-
ing—all influence the risk of breast cancer. Women exposed to low-level
radiation can develop breast cancer, and the risk is greater with younger
ages than with older ages. According to the BEIR V (1990) report, the
excess absolute risk of breast cancer in 25-, 35-, and 45-year-old women is
5, 4, and 2 in 10,000, per Gy (5, 4, and 2 in 100 per rem) respectively. The
BEIR VII (2005) estimate of this value is 10 per 10,000 person years per
Gy (10 per 100 person years per rem) at age 50. The risk of radiogenic breast
cancer apparently is reduced if the dose is given in divided exposures.
While in the past, the breast cancer risk from mammography was of
major concern, modern mammographic equipment is well designed and
properly shielded, resulting in significant reduction in radiation exposure
and hence a lower risk of breast cancer. According to the recommendations
of the American College of Radiology, women over 40 should have annual
mammography screening for breast cancer.
Other Cancers
Radiation-induced cancers in the thyroid, lungs, bone, skin, and other
organs have been found in the general population and are influenced by a
variety of etiologic factors such as heredity, occupation, age, sex, and hor-
monal level. For thyroid cancer, the BEIR VII (2005) reports the excess
absolute risk of 4.4 per 10,000 person years per Gy (4.4 per 100 person years
per rem).
Radiation Damage to Skin
The skin is sensitive to radiation because of the presence of highly radio-
sensitive structures such as hair follicles and sebacious glands. The radia-
tion effect on the skin is deterministic and has a threshold dose of about
100 rad (100 cGy). The primary skin reactions to radiation are erythema and
dermatitis. Initial erythema appears in a few hours to a few days after radi-
ation exposure, which is followed by dry desquamation characterized by
atrophy of epidermal papillae and vascular changes. In the third or fourth
week, erythema reappears with red, warm, edematous, and tender skin.
Temporary hair loss (epilation) can occur at this stage. Severe erythema is
Long-Term Effects of Radiation 253