RE: Assessing X-ray dose from 60KVp dental X-ray machine

["Vernig, Peter G." <Peter.Vernig@med.va.gov>]

Andrew,
You are almost certainly getting correct information.  After about 5 years
of consistently getting "M" which from our dosimetry vendor means "below
measurable" or less than 10 to 20 mrem I withdrew film badges from our
dental service personnel.  I believe most of their units operate at about
70-76 keV.  I did put in two room dosimeters in rooms where we have
panoramic dental units.  In case you are not familiar with such units.  They
move around the back of the patient's head doing about 220 degrees of a
circle and produce a panoramic x-ray that shows all teeth.  They operate at
about the same kVp [It is almost always fixed or not adjustable by
operators] or maybe just slightly higher.  When they get to the spine or the
section of the arc where the spine is, they typically boost either kVp or mA
to increase radiation for more penetration.  They operate for about 8 to 10
seconds and the mA, again usually fixed or adjustable by "patient profile"
[in other words the operator selects small, medium or large].  Any way mAs
are usually around 3-5 mA.  These units put out MUCH more radiation than the
standard units.  I have film dosimeters in our two panoramic rooms at the
approximate height of the beam.  Operators stand behind a shield with leaded
glass.  Even those dosimeters never show a reading above "M".

Dental personnel really do not need dosimetry IMO although I do think the
room dosimeter for a panoramic unit is a good precaution as if the unit were
grossly malfunctioning, there is a potential for exposure.

Peter G. Vernig, VA Medical Center, Denver, Colorado, USA
peter.vernig@med.va.gov
Solely my opinions!

-----Original Message-----
From: andrew_mcewan@nrl.moh.govt.nz
[mailto:andrew_mcewan@nrl.moh.govt.nz]
Sent: Thursday, July 22, 1999 10:50 PM
To: Multiple recipients of list
Subject: Re: Assesing X-ray dose from 60KVp dental X-ray machine




Sunil Nair wrote
___________________________________
Our dentist is using a 60Kvp X-ray machine. I have been issuing TLD(based
on CaSO4:Dy) for his personal monitoring but it always report zero dose. I
just want to make sure that the TLD reading is right. I am also a bit
worried about the dose anybody else may receive who are in the vicinity
but not behind the "gun". The doctor usually stand behind the X-ray "gun"
so the TLD might be right after all.  I would like to know how much dose
it produces in the vicinity (say, after scattering from the patient) and
how personal monitoring is done for the operating staff of such an energy
machine else where.

 ___________________________________
Our measurements show a person standing about 2 metres behind the back of
the
patient's head will be exposed to an effective dose of about 200
microsieverts
per year (0.2 mSv/y) based on a workload of 50 intraoral films a week.  If
the
TLD wearing period is 4 weeks there might be less than 0.02 mSv recorded,
depending on how far back the dentist stands.  Dose could be below the
reporting
level of the TLDs.

Andrew McEwan
_______________________
Andrew C McEwan PhD
National Radiation Laboratory
PO Box 25-099
Christchurch, New Zealand

Ph 64 3 366 5059
Fax 64 3 366 1156
Andrew_McEwan@nrl.moh.govt.nz



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