Response to Sandy's Response

["John R. Laferriere 671-8316" <John.R.Laferriere@dupontpharma.com>]

Sandy- If electronic dosimetry vendors are claiming both that their dosimeters
are good enough to serve as the dosimeter of record AND that their dosimeters
don't need NVLAP proficiency testing, then I certainly would disagree with
their position, even if 10 CFR 20 somehow provides a loophole.

In regard to your next comment:

"I am also saying that a dosimeter that does have an algorithm is 
more apt to be superior, be it film, TLD or whatever, when it is 
capable of defining the spectrum, and accounting for the 
appropriate dose calculation. If a doismeter is only calibrated to Cs-
137, and that is the only "dose algorithm" available, the resultant 
dose will be either an over-resposne or an under-response, 
dependent on the actual spectrum in which it was exposed."

So it sounds like we agree that a dosimetry vendor's algorithms are not
inherently superior to an EPD's algorithm.  My specific example was the 
Siemens EPD which has 3 pin diode detectors and a pretty impressive set of
energy response curves for photon AND BETA.  Our main use for the Siemens EPD
is in our Tc-99m generator manufacturing area, where we process kCI of Mo-99
each week.  It's the only epd with the ability to monitor shallow dose, and
I would certainly rank it far superior to pic's.  (Mo/Tc emits photons mainly 
in the 140 and 750 keV range, and has a Beta max at 1214 keV.)  We perform a
calibration check on each epd twice a year, using Cs-137 for deep dose checks
and Kr-85 for shallow dose response checks.  I also performed a one time check
with Xe-133 (photon only, 30-80 keV) which came out in good agreement with 
TLD and ion chamber measurements.  I seldom see variation greater than +/- 5%
with these calibration checks.

I agree with the view that a dosimeter (or survey meter for that matter) which
is only calibrated to one energy needs to be used with caution when radiation
fields vary from those used for calibration.  I will state again that it is
up to the user to ensure that any dosimetry (or survey meter) used is suitable
for the radiation fields that could be present.

Perhaps you misunderstood my position on epds.  I certainly wouldn't be eager
to toss our regular dosimetry out the window and go with epds for the dose
of record.  I guess I was reacting to your broad brush treatment of all
epd manufacturers when you said:

"In essence, 
> while the manufacturers swear that the "electronic dosimeter" is 
> not a processing dosimeter, such as found with dose determination 
> from a film or TLD, it is just that. There are built in algorithms and 
> parameters set and those that are hidden, within the device, and if 
           > those factors changes, so does the final dose reported."

It sounds almost conspiratorial.  You also make it sound like an algorithm
"hidden" within the epd is somehow a bad thing.  I guess it just comes across
(to me at least) as somewhat self-serving when a person employed by a dosimetry
vendor makes such sweeping statements about a competing technology when there
is at least one obvious exception to the one point calibration/algorithm epd
that you are presumably (correct me if I'm wrong) aware of (i.e. the Siemens 
EPD).  Maybe I'm being unfair with my last sentence.  If so, I apologize.

One last comment on your response:
                                        
"The EPD is a good dose 
control tool in that it makes the indivdual aware of their radiation 
exposure environment. The EPD response is only as good as to 
what it was calibrated, and, how the internal parameters are set."

I agree.  The same can be said for any radiation detection device.  Energy
response, angular response, etc. are factors that cannot be ignored with
any detector or dosimeter.  The user should also do some homework to verify
that a vendor's claims are valid.  I learned that lesson when we switched 
from Landauer to another vendor to save a few bucks, and didn't do any field
testing first.  We suddenly saw almost a 50% drop in cumulative dose in a
few groups.  Of course the vendor claimed NVLAP accreditation.  Needless to 
say, I haven't been too impressed with claims of NVLAP accreditation since
then.

My opinions only.

John Laferriere, CHP
DuPont Pharmaceuticals Co.
Medical Imaging Division
John.R.Laferriere@dupontpharma.com

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