Re: Embryo/fetal doses

["A. Hancock" <a.hancock@s1.cxwms.ac.uk>]

Mike Bohan wrote:

> Were your dose estimates, skin entrance dose, or were they corrected for depth
> dose?

----------------------------------------------------

Mike

As far as the work we did was concerned we used published depth dose
data to correct our entrance skin doses. Ref. Harrison, R.M. Phys Med
Biol 26: 657-670 1981. The TLD material we used was lithium borate
powder.

Incidentally I was a mere boy x-ray QA technician at the time and
therefore claim no responsibility for the accuracy of the dose
estimates.

I agree with the general opinion that in-utero exposures in diagnostic
radiology carry little, if any real risk.

A rule of thumb that has worked OK for me over the years is. Determine
the entrance skin dose - with backscatter, then assume 20% as an
estimate of fetal dose. This seems to tie in well with your assumptions.
That's reassuring.

On a different subject, another of my rules of thumb is that 3.0 mmAl
HVL @ 80kV will be equivalent to 3.0mm Al total filtration at 80kV (more
or less, depending upon waveform, target angle etc.)

Any more interesting rules of thumb out there? (NB radiotherapy
physicists hate these as they're so imprecise, i.e. outside their +/-
0.0000001% bounds! - only kidding!)

Cheers from England (Scotland votes on devolution today!)

Andy Hancock
a.hancock@cxwms.ac.uk