Re: Should we discontinue Pd-103 implants?

[Chris Alston <alstonc@odrge.odr.georgetown.edu>]

>References: <971114070814_412136808@mrin46.mail.aol.com>
>Date:         Fri, 14 Nov 1997 09:22:35 -0800
>Reply-To: wnikesch@flash.net
>Sender: Medical Physics Listserver <medphys@lists.wayne.edu>
>From: Walter Nikesch <wnikesch@FLASH.NET>
>Subject:      Re: Should we discontinue Pd-103 implants?
>To: Multiple recipients of list MEDPHYS <MEDPHYS@LISTS.WAYNE.EDU>
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>All "missing the points" aside, what really concerns me is the CHANGE in
>calibration.  And that change which recently took place was 8 to 10%.
>Three months ago when we measured 1.0 mCi seeds we got values around 1.0
>mCi +/- a few %.  Now we get 1.1 mCi for what is labelled as 1 mCi
>seeds.
>So what do we do?  Ask Theragenetics for some "calibrated" seeds and
>adjust the dose calibrator so it reads "correct".  The net result being
>that 115 Gy now is 8% more than 115 Gy previously.  I understand that
>this change brought the "calibration" back to what is was a few years
>ago.  So what were we doing the last few years?  Giving 105 Gy???
>It seems to me that if you change the calibration by 8% then the dose
>perscription should also change by 8% to keep everything the same.
>AND Theragenics should have notified its customers what they were doing.
>
>Walter Nikesch, Ph.D.
>wnikesch@flash.net
>
>
>CBS970@AOL.COM wrote:
>>
>
>> > Anyone who claims they know the exact
>> >  dimensions of the gland and can verify placement and stabilty of seeds
>> >  to millimeters can start to complain about small calibration
>> >  differences.
>>
>>   You missed the point.  We may well not be talking about SMALL differences
>> in calibration.  I sincerely hope we are.  But we don't know if the
>> manufacturer's calibration is accurate to within 10-20% or more.  Does anyone
>> have the ability to take a Pd-103 seed and accurately determine the activity
>> in a manner that does not rely in any way on any numbers provided by the
>> manufacturer at any time.  Clinical results aside, if the manufacturer's
>> calibration was off by 100%, how would you be able to tell?  Would you take
>> Varian's word that they calibrated your linac accurately without verifying it
>> with an independent set of equipment?
>>
>>                                                       - Carter Schroy
>