Læknablaðið - 01.10.1968, Síða 59

LÆKNABLAÐIÐ
217
practical purposes, a level of radialion safe for germ cells is more
than safe for all somatic cells.
Aside from deatli caused by acute radiation injury, the most
feared sequel of exposure to radiation is the development of
cancer. In experimental animals almost any tissue in the hody
can he led to develop cancer by appropriate application of radia-
tion. In man, ionizing radiation has produced cancer of the skin,
lung, thyroid, hone, bone marrow and rarely other organs. We
have already mentioned the lung cancer of uranium miners, indu-
ced by exposure of the bronchial epithelium to radiation from the
danghter products of the radon present in the air of the mines.
Currently, there is evidence tliat excess lung cancer exists in thc.
uranium miners of the soutlíwestern United 'States.7,8 No direct
connection hetween exposure of ljronchial tissues to radiation
from the radon daughters in the air of the mines and occurrence
of lung cancer lias been proved, hut three to four times as manv
cases of lung cancer occur in the uranium miners as in
the general population of comparable age. There is some evidence
that there is increasing frequency of lung cancer in those who
have had greater radiation exposure. There is also evidence thal
the cigaretta smokers among these miners may have especially
high risk of cancer. Tliere is some evidence, as yet inconclusive,
that a particular histologic type of cancer, tlie small ceil
undifferentiated form, is more prevalent among the miners.9
However, it is virtually impossihle by pathologic study of a given
cancer to determine whether or not it had been induced by
radiation. As a rule only by history of radiation exposure or by
finding changes characteristic of radiation injury in adjacent
normal tissues can one say that a given cancer was most probably
caused by radiation. Among the most helpful of these charac-
teristic changes in adjacent tissue are the presence of abnormal
fibrocytes with large and irregular nuclei, the presence of
hyalinized collagen and complete or partial obliteration of blood
vessels, which often show abnormal nuclei in their endothelial
cells. Many radiosensitive structures such as skin appendages are
obliterated.
It has long been known that chronic exposure of the skin
to radiation may cause cancer, hut the lesions produced are not
distinctive and cannot he distinguished from spontaneous cancers
or those caused by chemical carcinogens.
It is cleary estahlished by the experience of early United