INTRODUCTION
Radiation is one of the few,
health sciences
that spans
the entire range from constituting an ubiquitous
environmental agent of concern,
the control of cancer.
if not the only agent of interest in the
to being an effective therapeutic agent for
These characteristics place the former in the realm
of public health including accident statistics and epidemiology (Ph);
latter in the discipline of pharmacology,
toxicology,
the
and medicine (Md).
The same sets of characteristics that separate low-level exposure (LLE) to
radiation from high-level exposure (HLE) require that the primary
independent variable be
the amount of exposure to agent~carrying objects
(charged particles) in the environment of cells for the first; but mean
dose to the organ or other cell system for the second.
The basic radiation quantities and units in current use and defined by
the ICRU (J) were developed during that era in which a central theme was
‘therapeutic uses and thus early acute effects on an organ or a tumor:
clearly in the Md realm.
Thus,
the description and quantification of these
effects of HLE could, and still can be comfortably accommodated by those
quantities and units adopted early during this period.
variable was, and continues
depends
The principal
to be organ or tumor absorbed dose, on which
the fraction of organs or tumors responding quantally (1.e., an
all-or-nothing change of state,
from one of functional,
to essentially
permanent dysfunction or death).
However,
this state of affairs was not achieved without considerable
discussion and disagreements about how the “amount” or quantity of
radiation was to be defined.
In the physicist's eye, this quantity was
either the number of energy-carrying particles per unit area per unit time
flowing from the source, or alternatively the total energy flow from a
source,
per unit area,
i.e.,
either the particle or total energy fluence,
or a parameter of these variables.
standpoint,
However, from the physician's
these quantities expressing the strength of either the
4
radiation source or field were considered to be irrelevant: what mattered .
¢:
was that energy actually absorbed in tissue.
Se
In fact,
the “skin erythema
dose” unit of radiation "amount" had already been invented and used, which
1,.
by-passed any physical measurement beyond the duration of time spent in &
iny
Dns
radiation field calibrated against such a “biological dosimeter”.
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