Re: Re[2]: Lead Aprons in Dentistry

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

Ted de Castro said:

> On current dental units the tube housing IS very well shielded BUT the cone
> is NOT!  The beam is indeed collimated to be congruent with the open area
> at the tip of the cone (long plastic tube) - thus APPEARING to be a
> shielded tube - but it is not.  IF it were and the beam not so well
> collimated - there would be too much scatter from the tube and that would
> adversely affect image quality.

This is per a posting from a member on the MedPhysics LiustServer, a 
state inspector.. He states that the older houysings had more 
shielding comparec to the newer ones. Here is what he posted.. 
better using his words than mine. 

>>Housing leakage is definitely measurable from dental tube heads.  
>>The FDA says that leakage radiation shall not exceed 100 millirem 
>>in one hour at a distance of 1 meter.  The use of  "in one hour" 
>>instead of "per hour"  allows the manufacturer to stipulate a duty 
>>cycle for the machine.  One duty cycle I've seen is that the 
>>machine should only be operated for one second out of every 60.  
>>This would allow a instantaneous rate of 6000 mR/hr , or 1.7 mR/sec 
>>at 1 meter.  Typical exposure times depending on mA and cone length 
>>are on the order of 0.5 sec and if one assumes a distance of 0.25 
>>meters to the patients chest and it looks like you could get 3.4 mR 
>>per shot.  14 films or so in a full mouth series yields 47 mR at 
>>0.25 meters.  


------------------
Sandy Perle
Technical Director
ICN Dosimetry Division
Costa Mesa, CA 92626
Office: (800) 548-5100 x2306 
Fax:    (714) 668-3111
  
sandyfl@earthlink.net
sperle@icnpharm.com

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"The object of opening the mind, as of opening 
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