Re: dental x-ray web information

[Eric Cowdrey <ericc@mctrf.mb.ca>]

I am posting this comment for a colleague, Dr. Harry Johnson, who does not
presently subscribe to RADSAFE.


This is an interesting doscussion.  I wonder if I could pose the
following to the RADSAFE audience?

I subscribe to the overall comments made by Dr. Gibbs' in responding to the
observations of Dr. Weil.  I would, however, like to explore the comparison
of dental x-ray exposure a bit further.  I think that the use of a valid
comparison is important for conveying the perspective of the dose and the
risk to members of the public.

The comment that a typical dental radiograph is equivalent to a few days of
natural background radiation requires further discussion in order to
understand the quantitative basis of the comparison.  I assume that the
comparison refers to the gamma component of natural background (no radon).
Typically the gamma component of natural background near sea level amounts
to an effective dose of approximately 100 mrem per annum, +/- 20%.  A few
days exposure then amounts to an effective dose of approximately 1 mrem.

The skin entrance exposure of a bitewing dental x-ray at 70 kVp may be in
the range of 150-300 mR (D-Speed film) or 100-150 mR (E-speed film).

To convert the skin-entrance-exposure to an effective dose for this
comparison requires considerations that may include the use of the
dose-area-product concept and the tissue weighting factors, or some
equivalent method of using the skin-entrance exposure, determining dose at
the target organs, and applying the ICRP organ-weighting factors for the
limited body region exposed by the dental radiograph.

My questions are:  how has the conversion been applied in making the
comparison between the dental x-ray procedure and the effective dose due to
natural background?  And, secondly, what other reference effective doses
have readers found as the basis of comparison that are meaningful to members
of the public?

Dr. Harry M. Johnson
Manitoba Cancer Treatment and Research Foundation
Department of Medical Physics
100 Olivia Street
Winnipeg, Manitoba    R3E 0V9
CANADA

E-mail:  harry@mctrf.mb.ca

>At 09:22 AM 3/30/98, you wrote:
>>This is some commentary about the web site I mentioned to you recently.
>>
>>
>>>Date: Sat, 28 Mar 1998 22:26:13 -0600 (CST)
>>>Reply-To: radsafe@romulus.ehs.uiuc.edu
>>>Originator: radsafe@romulus.ehs.uiuc.edu
>>>Sender: radsafe@romulus.ehs.uiuc.edu
>>>From: "Gibbs, S Julian" <s.julian.gibbs@vanderbilt.edu>
>>>To: Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
>>>Subject: Re: dental x-ray web information
>>>X-Comment:  RADSAFE Distribution List
>>>X-Mailer: Simeon for Win32 Version 4.1.1 Build (17)
>>>
>>>If you isolate each sentence of Dr. Weil's response to "Are 
>>>Dental X rays Safe?", then much of it is correct.  The 
>>>problem is that it does not fit together.
>>>The radiation dose from typical dental radiography, 
>>>performed using state-of-the-art equipment and techniques, 
>>>is equivalent to a few days of natural background.  The 
>>>exact amount depends, of course, on the number and type of 
>>>exposures made.  There is no evidence of any harm from 
>>>these doses; neither is there evidence of absence of harm.  
>>>The risk, if any, must be infinitesimally small.
>>>Early radiologists have shown an increased incidence of 
>>>leukemia.  However, those entering practice since the 
>>>1930s, when radiation protection standards were introduced, 
>>>show no evidence of ill effects.
>>>It is true that diagnostic exposure, medical or dental, 
>>>should be limited to specific clinically-indicated 
>>>procedures, based on findings from history and physical 
>>>examination.  There is no recommended time interval for 
>>>repeat exams for all comers.
>>>Tubehead leakage and beam filtration are only two of many 
>>>factors that should be optimized for maximum efficiency of 
>>>diagnostic x rays: maximum information at minimum dose.
>>>There is no conclusive evidence that antioxidants have any 
>>>effect in protecting against the cancer risk from small 
>>>doses of radiation.
>>>
>>>***********************************************************
>>>S. Julian Gibbs, DDS, PhD               Voice: 615-322-3190
>>>Professor of Radiology                    FAX: 615-322-3764 
>>>Dept. of Radiology & Radiological Sciences
>>>Vanderbilt University Medical Center
>>>Nashville TN 37232-2670 Email:s.julian.gibbs@Vanderbilt.Edu
>>>



*************************************************

Eric Cowdrey
Radiation Protection Officer
Department of Medical Physics
Manitoba Cancer Treatment and Research Foundation
100 Olivia Street
Winnipeg, Manitoba  R3E 0V9
CANADA

Telephone: (204) 787-2166/4145
Fax:       (204) 775-1684
E-mail:    ericc@mail.mctrf.mb.ca