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Re: U.S. NRC proposes changes to shallow dose exposure limit
I think some of you know that I was on the NCRP committee that came up with the
10 cm2 limit. I'm very happy with this value for hot particles as a limit for
deterministic effects - especially as it is a unified limit of 50 rem for skin.
There is far too much to talk about over Radsafe, so if you want to talk about
how we came to 10 cm2 and its value, call me at 623 393 5200. As an example, 1
cm2 was never a biological endpoint from hot particles - it was equally
arbitrary as most effects studied on pig irradiations were 1-2 mm2 from the
betas. However, many particles are stepped on and attached to shoes - one
station just encountered this problem. And these particles expose larger areas
than 1 cm2 from the photons.
We discussed and wrote about the stochastic effects from hot particles and
determined them to be negligible, of course.
Mike Lantz, CHP
glen.vickers@EXELONCORP.COM wrote:
> I've been away from skin dose for a couple of years, but here are a couple
> issues I can think of right away.
>
> I believe the organ weighting factors assume uniform irradiation of the
> entire organ and that will essentially never be the case for skin
> contamination events.
>
> If they're thinking about changing the rules, then they need to also think
> about practical ways to calculate the quantities. Right now, if a person
> had varying levels of contamination on a planar source, the tech would take
> the highest direct reading with a 15.5 cm^2 GM probe and we'd calculate that
> as a 15.5 cm^2 source over a 1cm^2 receptor. Some might concentrate that
> reading as a 1 cm^2 source over a 1 cm^2 receptor, but that bumps up the SDE
> by about a factor of 15 for Co-60. I'd like to see some additional guidance
> about assumptions of the source size, because you can't really measure, and
> activity/probe area. With the new guidance should we take the reading/15.5
> cm^2 and apply that activity/cm^2 as a 10 cm^2 source over a 10 cm^2
> receptor? Different approaches yield signficantly different answers.
>
> Why change to 10 cm? The calculated doses will drop significantly. Why not
> just increase the limit over the same 1 cm^2 if we think we are overstating
> the stochastic risks from planar sources?
>
> What about deterministic effects from hot particles? The NRC's enforcement
> guidance stated that a limit of 75 uCi-hr would be applied in addition to
> the 50 rem SDE. NRC (IE 90-48, NCRP 106) Also hot particle dose is not
> SDE, but SD or hot particle dose. The NRC needs to codify gudiance for
> point and planar sources. They did a good job with the enforcement
> guidance, but now would be the time to address the issue appropriately.
>
> Glen Vickers
>
> > -----Original Message-----
> > From: Sandy Perle [SMTP:sandyfl@EARTHLINK.NET]
> > Sent: Thursday, July 12, 2001 9:58 AM
> > To: radsafe@list.vanderbilt.edu
> > Subject: Re: U.S. NRC proposes changes to shallow dose exposure limit
> >
> > > This is in keeping with the recommendations found in NCRP 130.
> >
> > While this proposal is an improvement, the NRC needs to move towards
> > acceptance of dose weighting. The skin, being an organ, should be
> > viewed as other organs are, and where there are weighting factor
> > applied, if the NRC would accept the methodology, such as what is
> > outlined in HPS N13.41-1997.
> >
> > In my opinion, it is still unrealistic and not logical to assign a
> > SDE based on the highest 1 cm, 10 cm or whatever number of cm's one
> > wants to consider, when in all practicality, the cumulative dose
> > effect to the person is insignificant. Now, for very high dose
> > particles, I can agree that averaging needs to be assessed. However,
> > for the general population of workers, using the highest dose nees to
> > be re-thought.
> >
> > ------------------------------------------------------------------------
> > Sandy Perle Tel:(714) 545-0100 / (800)
> > 548-5100
> > Director, Technical Extension 2306
> >
> > ICN Worldwide Dosimetry Service Fax:(714) 668-3149
> >
> > ICN Pharmaceuticals, Inc. E-Mail:
> > sandyfl@earthlink.net
> >
> > ICN Plaza, 3300 Hyland Avenue E-Mail: sperle@icnpharm.com
> >
> > Costa Mesa, CA 92626
> >
> > Personal Website: http://www.geocities.com/scperle
> > ICN Worldwide Dosimetry Website: http://www.dosimetry.com
> >
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