Biomedical Engineering Reference
In-Depth Information
Fig. 13.5
Example from Life Span Study.
Excess relative risks of solid cancer for
Japanese atomic-bomb survivors exposed at
age 30 who attained age 60. Inset shows the fit
of a linear-quadratic model for leukemia, to
illustrate the greater degree of curvature
observed for that cancer. See text. [Reprinted
with permission from Health Risks from
Exposure to Low Levels of Ionizing Radiation:
BEIR VII Phase 2, © (2006) by the National
Academy of Sciences, courtesy of the National
Academies Press, Washington, DC.]
acterize the Life Span Study, such investigations can provide some insight into
issues outside the scope of the Japanese data—for example, protracted exposures.
The following three examples illustrate some findings from medical exposures of
humans.
First, X rays were used in the 1930s and 1940s to shrink enlarged thymus glands
in children. Treatments could deliver a substantial incidental dose to a child's thy-
roid, one of the most sensitive tissues for cancer induction by radiation. An ab-
normally large number of benign and malignant thyroid tumors developed later in
life among individuals that underwent this procedure as children for treating the
thymus.
Second, it was also common in the 1940s and 1950s to use X rays to treat ring-
worm of the scalp
(tinea capitis)
in children. A dose of several Gy was adminis-
tered to the scalp to cause (temporary) epilation, so that the hair follicles could
be more effectively treated with medicines. This procedure also resulted in a sub-
stantial thyroid dose. Following the establishment of the State of Israel, ringworm
of the scalp reached epidemic proportions among immigrants coming there from
North Africa. Israeli physicians treated over 10,000 immigrating children, who later
showed about a sixfold increase in the incidence of malignant thyroid tumors, com-
pared with unirradiated controls. A survey of 2215 patients similarly treated in New
