Re: Mice and elephants

[Ccja@aol.com]

The AAPM & HPS held a joint meeting in Boston in 1995.

In re the question of the radiobiological equivalencies of exposure: in
health physics, for the purposes of routine protection of persons (in
contrast to, let's say, basic research into dosimetry) the value most
commonly used, where exposure to penetrating external radiation is the
concern, is the deep dose equivalent (DDE). That is, the dose equivalent at a
depth of 1 gram/sq.cm. (i.e., 1 cm.) in soft tissue, starting at the exterior
of the body. This is merely a convenient indexing point. Most of the organs
which we are really protecting, e.g., the lungs, thyroid, female gonads, red
bone marrow, etc., are at much greater depths, and sometimes pretty well
shielded (RBM). Even the male gonads are well shielded, in the lateral view.
Also, occupationally exposed individuals, and the general public, are not
usually exposed to, for instance, the direct beam of a medical linac, in
which electronic equilibrium may not be achieved before a depth of several
centimeters.

So, I would think that a sumo wrestler (or an elephant), would receive less
"real" exposure, if the DDE is the measure of said exposure, than a jockey,
or, more to the point, a small child (or a mouse), for the same reason that
fetuses receive rather less exposure than the expectant (or unknowing)
mother, in most cases.

chris alston
ccja@aol.com