eet aay “gh tment Set
~
.
.~ pibtaSayy Pe neeati Aat oeetalinnRa dn eas one oe
=
the value of Z alone.
Then the RBE would be simply the ratio of the value
of z for the standard,
to that of the high-LET radiation,
The result is shown in Fig. 10,
in which an HSEF, f.e.,
the
probability of a cell responding quantally, Pq, vs. 2 is plotted.
the HSEF,
In using
the entire distribution of 2 is wultiplied by the HSEF to obtain
values for the cell risk from a radiation of any quality.
in the Fig,
the RBE utilizes only the mean values uf
However, as. seen
z, and as such the RBE
ratio provides an indication of the effectiveness of a radiation that
delivers predomtnantly high cell doses, relative to the standard that
delivers essentially only small cell doses.
Thus it is seen that the RBE
is at best simply a crude method of approximating in stepwise fashion what
an aSCF presents as a continuous function.
s
It ts conceptually questionable
because as used it is a confounded ratio, and employs only average values
of cell dose,
The latter would be valla only if the cell risk were
proportional to cell dose, which Lt clearly is not.
Nl 1
-Yooee
‘
(RBE)
f
P,, at z-
RELATIVE
BIOLOGICAL
EFFECTIVENESS
Fig. 19
kelationship between the HSEF and RBE, taken as the
ratio of Z for the standard, to that for a high-LET radiation,
The RBE is a crude approximation to the HSEF, in that it is
the ratio of the mean of the relatively large cell doses
delivered by a lulgh-LET radlation, to the mean of the relatively
low cell doses delivered by the low-LET standard radiation.
See text for additional explanation.
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