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Re: DAP Meters -- Comment
>Date: Wed, 22 Jul 1998 20:08:14 -0500
>Reply-To: Medical Physics Mailing List <MEDPHYS@LISTS.WAYNE.EDU>
>Sender: Medical Physics Listserver <medphys@cwis-20.wayne.edu>
>From: "Joel E. Gray, Ph.D." <joelgray@M3.SPRYNET.COM>
>Subject: Re: DAP Meters -- Comment
>To: MEDPHYS@LISTS.WAYNE.EDU
>
>I would like to agree with Robert but put more emphasis on the fact that
>the values produced by the DAP meter are unknown to most radiologists, all
>other physicians, and many medical physicists!! What does a roentgen-cm**2
>mean, besides being a mixture of old and SI units! It is an extremely
>difficult topic to explain to non-physicists.
>
>Questions which arise-- how many roentgen-cm**2 before I see erythema or
>epilation? Answer: it depends on the field size! What is the risk of
>developing cancer to a specific organ, e.g., the breast, from 100, 1,000,
>or 10,000 r-cm**2? Answer: it depends on the field size!
>
>In case you can't tell, I am not a proponent of DAP (and I know I will hear
>from John Cameron on this one) since folks don't understand it. However,
>at least one firm (I believe it is PTW) makes a DAP meter with a sensor in
>the center that allows one to define the exposure in roentgens at some
>point so it would be relatively easy to estimate the entrance skin
>exposure. Anyother firm, Clinical Microsystems, makes a unit, although not
>inexpensive (about $15K per x-ray tube) which gives the actual entrance
>exposure in air.
>
>Two other solutions, although these do not provide the radiation exposure
>rate "speedometers"-- One firm makes a device which uses a solid state
>sensor and fiber optic probe to measure skin exposure. The sensor is
>placed on the patient-- so the accuracy is VERY questionable since it is
>difficult to position the detector in the center of the field and keep it
>there during the procedure. However, the sensor could be placed on the
>front of the collimator and used like the PTW device I mentioned above, if
>properly calibrated.
>
>Finally, and I think this is the best solution, we should encourage the
>x-ray equipment manufacturers to provide the entrance skin exposure, both
>cumulative and instantaneous exposure rate, for all systems (I believe the
>FDA is considering requiring this for systems used for vascular imaging and
>interventional procedures). The information is already in the generators
>in digital form so it would be relatively simple for them to calculate the
>entrance skin exposure and display it in a manner similar to that of
>Clinical Microsystems.
>
>If someone from the FDA is monitoring this listserver, I would appreciate
>hearing what the regulations regarding this will include and what the
>status is, i.e., how soon will this be required and will it be required
>retroactively or only for equipment manufacturered after a specific date?
>
> Joel
>
>Joel E. Gray, Ph.D., Consultant
>2804 Second Street SW, Suite 334
>Rochester, Minnesota 55902
>
>Ph 507-286-8910
>Cell Ph 507-269-4247
>Fax 507-286-8910
>e-mail joelgray@m3.sprynet.com
>
>
>
>
>
>
>
>
>>The DAP concept is an excellent one IF one understands what the readout
>>means...
>>For instance: if the ABS system on the fluoro is adjusted correctly, the
>>readout of the DAP meter should barely change when different II fields are
>>selected. I had a situation at my previous institution where we had a very
>>early DAP system (I think from PTW--it was orange!) installed on a C-arm in
>>the OR on a trial basis. An orthopod was putting some hardware in a
>>patient's knee under fluoro and purposely decreased the field size on the
>>II to the smallest. The logic: since the DAP meter showed the same
>>reading, why not minimize the field size and save on dose?
>>
>>The point of this anecdote is that it is important, however nerdy the idea
>>may appear, to give the DAP users a good in-service!
>>
>>Robert
>>
>>Robert G. Zamenhof, Ph.D., D.A.B.R.
>>Director, Radiological Physics Section
>>Department of Radiology
>>Beth Israel Deaconess Medical Center
>>1 Deaconess Road, Boston, MA 02215
>>Tel: (617) 667-0175; Fax: (617) 975-5233
>>Beeper: (617) 667-5555 #8075
>>
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Chris Alston
alstonc@odrge.odr.georgetown.edu
I am not here a representative of my employer.