~ 35 —
the data from the Atomic Bomb Casualty Commission in Japan are still
fragmentary and will not be complete for a number of years, they can
be interpreted as consistent with the concept that large single doses
of radiation to man do definitely increase or accelerate the appear-
ance of leukemia (27).
The data which have accumulated on the incidence
of leukemia among radiclogists is consistent with the hypothesis that
large total doses in the vicinity of several hundred to 1000 r and more,
even when received in small increments, are levkemogenio in some individuals.
Finally, the study of Court-Brown and Doll in Fngland on the incidence of
leukemia in radiation-treated patients with spondylarthritis ankylopoietica
suggests that large doses of radiation to the bone marrow may result in
leukemia. (10)
The control group for this study is so small that one
really has no information on what the inoidence of leukemia in these
patients would have been without radiotherapy.
However, if compared with
the incidence of leukemia generally among the British population as a
whole the effect is clear-cut.
The available experimental data fron
fairly extensive studies indicate that depending on the type of leukemia
the induction curve may be either sigmoidal or linear.
For doses of less
than 100 r in humans and in statistically significant numbers of experi-
mental animals there are very little data.
Whether or not there is a
threshold for leukemia induction by sadiation is not definitely Imown.
While it has been generally acecpted among students of leukemia that there
is some dose of radiation perhaps in tne vicinity of 50 r below which
leukemia is not induced, Dr. F, B. Lewis of California Institute of
Technology (22), and Dr. Yerdin Jones of the University of California at
Berkeley (17) have propose¢ the nyvothesis that leukemla induction from