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Re: Hologic QDR X-ray Bone Densitometer RAD Protection

>November 24, 1993 Dr. James Sims of UNT Fort Worth writes:
>> We have a physician that plans to acquire a model QDR-1500 Hologic
>> QDR Bone Densitometer.  I have reviewed the sales literature that
>> suggests that additional lead shielding of walls is not needed and
>> that the operator console need not be shielded.  Does anyone have
>> experience with these units and willing to share the protection
>> measures taken?  I'm particularly interested about experiences in
>> the Texas regulatory environment.
>The University of Southern California has recently acquired this same bone
>densitometer for use in the Excercise Sciences department.  The Radiation
>Protection Department surveyed the instrument in operation with a spine phantom
>in place and the scatter results were 0.9 to 1.4 mR/hr at one foot from
>phantom and 0.2 mR/hr at the head of the table (approx. 3 feet) 
>and < 0.1 mR/hr at the operators station (approx. 5 feet).  There was no 
>detectable x ray in the adjacent office, a distance of about 5 feet with an
>adjoining wall.  Tube head leakage was also measured and found to be zero
>at 1 meter.  Measurements were made with a Keithley Model 36150 Integrating
>Radiation Survey Meter.  As the above measurements indicate, no shielding
>was required.

I have done a radiation survey on a QDR-1000 using the Kiethley 36150 
(build-up cap removed) and the spine phantom provided by Hologic.  At 
a distance of 17 cm the integrated exposure for a 395 second spine
scan was 131.5 micro-R (=1.20 mR/hr), at 100 cm (lateral to the couch)
the exposure was 5.6 micro-R (=0.051 mR/hr) and at 170 cm lateral to
the couch, where the operator sat, the exposure was 0.46 micro-R
(=0.004 mR/hr).  I also had to consider that each patient has a hip
_and_ spine scan done.  The hip scan takes 471 seconds.

In addition, in the State of Ohio, these units are required to be
registered and are considered radiographic equipment and must comply
with all rules and regulations governing such.  This, BTW, is something
I attempted to contest with the state but to no avail.  In order to 
comply with some of the regs, I had to use Hologic documentation (i.e.
HVL; talk with Thomas Kelly, Sr. Scientist at Hologic) and request
some special exemptions.  I would be interested in talking with others,
particularly in Ohio, about their experiences registering these 

Hope this helps!


Carl Landis                        ad198@yfn.ysu.edu
Medical Physics Dept.              216-740-4409
Southside Medical Ctr.             FAX:  216-740-6581
Youngstown, OH  44501-0990         "My opinions only!"