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Re: Lead aprons in nuclear medicine

David - 

There is  an article by Paul Murphy, Yuexin Wu and Sharon Glaze, published in Radiology 
1993; 186: 269-272 entitled "Attenuation Properties of Lead Composite Aprons".
The authors compare the attenuation of both the new composite light-weight aprons  and 
conventional lead aprons for 60, 80, 10 and 120 kVp x-rays, as well as for monoergetic 
gamma photons at 31, 59, 81, 140 and 364 keV, respectively corresponding to x-and gamma 
ray emissions from Xenon-133, Americium-241, Tc-99m and I-131.  They also performed 
attenuation measurements of the bremmstrahlung x-rays emitted by a P-32 source in a 
glass vial.

Many radiology departments are using the new composite aprons (which contain lead as 
well as other elements like tin, yttrium and copper, etc.) because they weigh less and 
are more compfotable to wear.  Generally, the manufacturers measure the attenuation 
rates only for conventional diagnostic x-ray energies, NOT for gamma rays. 

Murphy et al concluded that the photon-attenuating properties were quite adequate 
(attenuation  >88%) for x-rays up to about 120 kVp.  However, for the 140 keV gamma rays 
from Tc-99m, the attenuation of the 0.5 mm "lead-equivalent" aprons is in the range of 
35 - 40 %, compared to 70 - 78% for the conventional 0.5 mm lead apron.  A 140 keV gamma 
ray is ROUGHLY equivalent to a 280 kVp  x-ray, much higher than the diagnostic x-ray 
range for which the lead composite "lite" aprons are designed.  The performance was 
corresponding poorer for the higher energy gammas from I-131. 

Generally, the manufacturers measure the attenuation rates of their protective aprons 
only for conventional diagnostic x-ray energies, NOT for gamma rays. In most cases they 
were unaware (I don't know if that is still the case) of the considerably poorer 
performance for gamma rays emitted by most of the radionuclides used in nuclear 
medicine.  Certainly most vendors representatives have no idea of this critical 
difference and are happily promoting the new "lite" aprons in both nuclear medicne and 
diagnostic x-ray.

This can sure be a problem for the typical nuclear medicine departments which often are 
a subsection of the hospital radiology or imaging department.  First, most  nuc. med. 
types are unaware of the poorer attenuation properties of these "lite" aprons, and the 
purchasing is often done through the radiology department,  which assumes that the 
aprons will be equally effective in attenuating both x- and gamma rays. Often, 
conventional and "lite" aprons are assumed to be equivalent and are swapped back and 
forth between radiology and nuclear medicine. 

The result is that nuc. med. staff have a false sense of security when wearing the 
"lite" aprons. 

One of the nuclear medicine departments I consult to purchased some new aprons and were 
quite proud of these new fashionable and comfortable items - that is - until I arranged 
to have attenuation measurements done for gamma emitters of various energies. 
Needless to say, the "lite" aprons were returned and exchanged for the conventional but 
heavier units which attenuated almost twice as well.

I circulated a warning memo to the other 8 nuclear medicine departments in Manitoba to 
which I  consult. I also wrote to the apron manufacturer, requesting that they mention 
the attenuation performance difference in its advertising literature and educate its 
sales reps about which type of apron was suitable for which application. I have no idea 
if the company took any heed of my request, as I never received a written response.  

I hope the above is useful.

Best wishes

Karin Gordon
Radiation Safety Office 	phone 	(204) 787-2903 
Health Sciences Centre		fax	(204) 787-1313
Winnipeg, Manitoba		e-mail   kgordon @cc.umanitoba.ca


David Scherer wrote:
> I was asked for any references to published work that assess the efficacy
> of lead aprons for use  by nuclear medicine workers.  We have discussed the
> fundamental principles (e.g.,  0.5 mm of Pb will shield x-rays much more
> effectively than Tc-99m gamma rays).  However, I was asked whether there
> are any published results on the matter.
> Thanks for your help.
> Dave Scherer
> scherer@uiuc.edu