Re: Response to Sandy's Response & NVLAP

["Sandy Perle" <sandyfl@earthlink.net>]

> 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.

John,

I agree completely with what you said above. I will add that many 
misinterpret what NVLAP accreditation really means. NVLAP 
signifies that a processor meets the "minimum standards" as 
stated in 15CFR285. Passing the Proficiency Testing only means 
that the processor has tested and passed Categories I and II with a 
|B+s| < 0.30, and Categories III through IX with a |B+s| <0.50. As 
you stated, one should always ask for the actual summary 
provided by NVLAP. The key to any processor isn't necessarily the 
Proficiency Testing, but what the various On-Site Assessments 
have determined. I suggest that anyone who uses someone else to 
perform their dosimetry, or in-house, that the On-Site Assessment 
Report be obtained, and reviewed. It is the programmatic factors 
that I believe carry the most weight, that ultimately support 
whatever the Proficiency Testing showed. I'd also ask for their 
internal QA irradiation data and external confirmatory measurement 
data, as routine submittals.

As far as the comment regarding the cumulative exposure dropping 
after switching processors, there are many factors that should be 
evaluated. By mentioning these factors, I am not suggesting that 
what you had from either processor was correct, or incorrect, just 
mentioning factors. To determine what is correct, one must 
evaluate the NVLAP data, as already discussed. Of course this is 
exposure within a controlled sterile environmemt. Field use and 
field irradiations need to be conducted to determine the most 
effective dose reported. Are there unusual geometry considerations 
that need to be accounted for. What secondary dosimetry and is 
there a dose rate issue, or energy dependency issue to be 
addressed. How is the dosimetry worn, stored, etc. By only point 
is that to assume one processor is more accurate than another 
needs further assessment. Perhaps the processor you believe to 
be incorrect may actually be more accurate. I'd also suggest that 
you determine what standard the processor uses. I am aware that 
some use the former ANSI N13.11-1983 version, when the current 
version is the 1993 standard. In that change, the Ck values for low 
energy x-ray changed dramatically. There is also a change of + 3% 
for the Cs-137 Ck. So, all factors need to be addressed.

Getting back to the original topic at hand, the EPD, you mentioned 
many of the tests you conducted. That is commendable. Many are 
not aware that EPDs are dose rate dependent, energy dependent 
and angular dependent. All of these factors need to be understood, 
and once accomplished, the facility can better control the work 
within their area.


Sandy Perle
E-Mail: sandyfl@earthlink.net 
Personal Website: http://www.geocities.com/capecanaveral/1205

"The object of opening the mind, as of opening 
the mouth, is to close it again on something solid"
              - G. K. Chesterton -
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