X-Ray Shielding Requirements

["Michael P. Grissom" <MIKEG%SLACVM.bitnet@vmd.cso.uiuc.edu>]

Forwarded-from: MIKEG

1.  Since this is a small message, I did not crop MAJ Jordan's item
below.  Regarding the change in regulations, I believe the NRC and
agreement states are involved in cases where by-product material is
used (high dose rate brachytherapy, or even conventional intracavitary
and interstitial therapy) in special shielded rooms or conventional
rooms with portable shielding.

2.  Some agreement states (e.g., California) are looking at the
question of shielding to 100 mrem very closely for THERAPEUTIC linear
accelerators and x-ray machines.  In several installations where the
conservative assumptions provided by the NCRP were not used (based
on the recommendations of architectural consultants justifying
their existance by reduced shielding costs) there IS a problem!  I
would refer you to our former RSO (Richard McCall, I believe he is
listed in the HPS directory) for some practical examples.

3.  In general, most diagnostic units won't be greatly impacted because
most shielding (even spare) is sufficient.  Occasionally I had trouble
with higher occupancy adjacent spaces, but nothing to seriously
challenge 100 mrem per year.  I demonstrated that, of course, by
posting an area monitoring TLD (or film badge in the bad old days)
at the appropriate locations to intercept maximum primary or secondary
beams based on room surveys and techniques used analyses.
----------------------------------------------------------------------
The opions expressed above are those of the author alone and do not
not represent those of the Stanford University or the US Department
of Energy.
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                         - - - - Forwarded Text - - - -


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From: MAJ Don Jordan <djordan@osiris.cso.uiuc.edu>
To: Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
Subject: X-Ray Shielding Requirements
X-Listserver-Version: 6.0 -- UNIX ListServer by Anastasios Kotsikonas
X-Comment:  Radiation Safety Distribution List



This is the first time I have tried to send a message so will apologize
ahead of time for any breechs of internet decorum.  I am looking for any
information relating to the practical impact of the 100 mrem
nonoccupational annual dose limit on medical/industrial x-ray facilities
whose shielding requirements were initially determined using NCRP 49 and
the previous 500 mrem/yr nonoccupation dose limit.  As you might guess,
retrospectively applying the NCRP criteria with 100 mrem limit
significantly increases the calculated required shielding.  In fact, all
other parameters being the same, using the NCRP methodology with the 100
mrem limit would require many of our medical/industrial x-ray facilities
to be extensively modified to add additional shielding.  As I believe the
NCRP 49 calculational methodology is very conservative (overestimates
shielding required), the practical impact, as shown by the results of
environmental/area surveys or other methods, may not be that great.  Any
information or view points would be appreciated.