Re: Radiation monitoring badges in cine/floro exams

["H.Wade Patterson" <hwade@talltown.com>]

Group:
Tupin, Edward A. 301-827-1230 Fax 594-4760 wrote:
> 
> Those of you looking for further guidance on use of badges for external
> exposure monitoring might want to get NCRP Report 122 "Use of Personal
> Monitors to Estimate Effective Dose Equivalent and Effective Dose to
> Workers for External Exposure to Low-LET Radiation" Issued Dec 27, 1995.
> 
> It describes how to calculate the dose quantities, and also offers
> guidance on badge placement, including the specific situation of
> fluoroscopy where a lead apron is worn.
> 
> Ed Tupin
> RSO, Center for Devices and Radiological Health
> EAT@fdadr.cdrh.fda.gov
> (301) 827-1230
> Fax:  (301) 594-4760

John Cameron has this to say about NCRP 122. These are his observations;
and I agree with them.

In 1990 NCRP Report 104 on Relative Biological Effectiveness of
Radiation of Different Quality was intended to improve the value of Q
(now WR) by reviewing RBE values in the scientific literature. The
committee concluded that it was not possible to give a value for Q (now
WR) because of the wide range of experimental results. It recommended
choosing an appropriate value.  Three years later NCRP Report 116 (1993)
continued to use Equivalent dose with the old Q values re-labeled WR
values, even though NCRP Report 104 stated that Q (now WR) values could
not be determined.

The NCRP did not assign a committee to evaluate the scientific validity
of tissue weighting factors. However, ICRP published modified values of
WT in 1991 when they changed the name of the quantity to Effective dose.
The changes in WT do not seem extreme but they had a significant effect
in calculating the Effective dose based on a dosimeter worn at the neck
outside of a protective apron for persons doing fluoroscopy.   NCRP
Report 122 (1996) explains how to calculate both the Effective dose
equivalent (using its 1977 WT values) and the Effective dose (using its
1991 WT values). In the first case you divide the badge reading in Sv by
5.6 and in the second case you divide it by 22.  There is a decrease of
375% from 1977 to 1991! . Since Effective dose equivalent and Effective
dose are both estimates of radiation risk, a difference of 375% suggests
a significant error in one or both sets of WT values.

-- 
H.Wade Patterson
1116 Linda Lane
Lakeview OR 97630
ph 541 947-4974

"When we hold a conclusion inviolate, sometimes the assumptions require
certain adjustments."  Harold Hopfenberg, Prof. of Chem. Eng., N.
Carolina State University.