Thyroid Depth

[Ccja@aol.com]

Someone posted a question on one of these boards, last week, about (I think)
the amount of tissue overlying the thyroid in a phantom. I seem to have
erased the message, but it's my recollection that the knowledge-seeker did
not specify which phantom he was interested in. We use the neck phantom
specified by ANSI N44.3-1973. In the AP view, there is 0.5cm of "tissue"
(polymethylmethacrylate) overlying the thyroid, at the shallowest point, and
the depth to the thyroidal midline is 2.0cm.

I believe that there have been a couple of papers recently, in Health
Physics, which showed that, at distances of 30cm., or more, the geometrical
differences between the various phantoms (there are at least four that are
well-recognized, we should not speak of the paint cans full of rice, and
other, similar, homemade varieties) become negligible.

chris alston
ccja@aol.com