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Re: Early Morning Phenomenon
>Date: Tue, 12 May 1998 21:43:11 -0500
>Reply-To: Medical Physics Mailing List <MEDPHYS@LISTS.WAYNE.EDU>
>Sender: Medical Physics Listserver <medphys@lists.wayne.edu>
>From: "Gary J. Adler" <gadler@GTE.NET>
>Subject: Re: Early Morning Phenomenon
>To: Multiple recipients of list MEDPHYS <MEDPHYS@LISTS.WAYNE.EDU>
>
>Just read your post and the replies and I thought of a few possibilities.
>
>With regard to your question concerning the change in measured electron
output, I think the important point to note is that it happened on both
machines on the same day! I find it hard to believe that a malfunction or
change occurred naturally in both machines at the same time. In the past
when I found changes in measured output of all my electrons on my Siemens
machine, I also discovered that the service engineer had replaced the temp
sensor in the head the night before and in re-balancing the Temp-pressure
circuit had affected the output. This sort of change should affect all
electron energies the same. So an obvious question is:
> Did the service engineer work on both machines the previous night?
>
>Other possibilities include:
> Are both machines on the same chilled water, or were the
measurements made at a different time in the warmup phase of the
accelerators? The temp of the machines at the time of the measurement can
significantly affect the result. On our Siemens KD after warmup, a
difference in measurement time of 1/2 hour will make over a 1-1.5% change
in measured output. After about one hour, the machine is much more stable as
to output. Our morning output checks take this into account and we have a
specific protocol as to warmup steps and order of measurment.
>
>A final thought - you said the room temperature was 22 C. Where were the
chamber and phantom kept and what were their temperatures?
>
>Good luck. It would be nice to hear what you find to be the cause.
>
>Gary Adler (gadler@gte.net)
>Hux Cancer Center
>Union Hospital
>1606 N. 7th Street
>Terre Haute, IN 47804
>
> *****
>Frequently Asked Questions (FAQ) for Medphys at:
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