No Subject

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

>From: Chris Alston <alstonc>
>Subject: AW: AW: Effective Photon Energy of X-rays
>
>>Date:         Fri, 31 Jul 1998 08:30:36 +0200
>>Reply-To:     Medical Physics Mailing List <MEDPHYS@LISTS.WAYNE.EDU>
>>Sender:       Medical Physics Listserver <medphys@cwis-20.wayne.edu>
>>From:         Seelentag Wolfhart KSSG_RO <rot1@MS1.KSSG.CH>
>>Subject:      AW: AW: Effective Photon Energy of X-rays
>>To:           MEDPHYS@LISTS.WAYNE.EDU
>>
>>>Von:   Ubaldo Huerta[SMTP:uhuerta@UNIMET.EDU.VE]
>>>Gesendet:      Freitag, 31. Juli 1998 00:07
>>>An:    MEDPHYS@cwis-20.wayne.edu
>>>Betreff:       Re: AW: Effective Photon Energy of X-rays
>>
>>>....<snip>
>>>>>>  I want to apply correction factor of effective photon energy to doses
>>>>>measured by a BeO TLD dosimetry.As you know I should estimate an effective
>>>>>photon energy for 150 kVp x-rays. any information regarding computation of
>>>>>effective energy for X-rays are appreciated.
>>...<snip>
>>>>
>>>>Dear Chris and Mehra,
>>>>
>>>>a loooong time ago I have been measuring lots of x-ray spectra up to 300
>>>>kVp. The result was a catalogue, which I guess will no longer be
>>>>available (review in Medical Physics 9 (1982) 134-135). One of the side
>>>>effects was a paper entitled "Equivalent half-value thicknesses and mean
>>>>energies of filtered x-ray bremsstrahlung spectra" by W.W.Seelentag and
>>>>W.Panzer (Brit. Journal of Radiology 53 (1980) 236-240). There you'll
>>>>find tables helping you to estimate mean energy from kVp and first HVL
>>>>(just kVp alone is not sufficient to estimate mean energy with any
>>>>satisfactory accuracy).
>><snip>
>>
>>>of course you need measure second HVT, but I donīt remember any old table
>>>best regards
>>>ubaldo
>>
>>Well - you need to know the "homogeneity coefficient" of the beam, i.e.
>>the ratio first/second HVL. There is a nomogram in the above cited
>>paper, however, allowing you to determine homogeneity from kVp anf first
>>HVL - with sufficient accuracy to then determine mean energy. You should
>>not use the nomogram for any other purpose without careful consideration
>>of its limitations.
>>
>>Best regards  -  Wolf
>>--------------
>>Wolf W. Seelentag, PhD, e-mail : wolf@swissmail.com
>>Klinik fuer Radio-Onkologie, Kantonsspital,
>>CH - 9007 St. Gallen, Switzerland
>>Tel : +41-71-4942233   Fax : +41-71-4942893
>>
>>                    *****
>>Frequently Asked Questions (FAQ) for Medphys at:
>>http://www.mindspring.com/~sherouse/MPFAQ/
>>
>>Archives of recent Medphys postings at:
>>http://www.escribe.com/medicine/medphys/
>>
Chris Alston
alstonc@odrge.odr.georgetown.edu
I am not here a representative of my employer.

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