[ RadSafe ] Myth or Fact? (Dental dose)

Fri Aug 25 07:04:06 CDT 2006

A survey was performed of operating dental units in
the US in 1999, with the results made available in a
report dated 11/03.  According to Tables 10 and 11,
the average entrance skin exposure (ESE) was 327 mR or
mGy (not mrem).  For D and E speed films the results
were 233 and 53 mR or mGy, respectively in Tables 12
through 15.  

For cephalometric films, the average ESE was 20 mR or
mGy as listed in tables 42 and 43.

The report is at
http://www.crcpd.org/Pubs/NEXT_docs/NEXT99Dental.pdf

--- Robert Atkinson <robert.atkinson at genetix.com>
wrote:

> Hi,
> In the UK the use of 50kV inter-oral X-Ray sets was
> phased out from
> about 1990 with a ban from 2001 (some special
> exceptions), along with
> other measures to reduce the dose. These include
> adjustable output and a
> minimum focus to skin distance of 200mm.
> 
> See <
>
http://www.hpa.org.uk/radiation/publications/documents_of_nrpb/abstracts
> /absd5-3.htm >
> 
> Regards,
> Robert Atkinson.
> 
> -----Original Message-----
> From: radsafe-bounces at radlab.nl
> [mailto:radsafe-bounces at radlab.nl] On
> Behalf Of Yoshihiko Hayakawa
> Sent: 25 August 2006 09:30
> To: radsafe at radlab.nl
> Subject: Re: [ RadSafe ] Myth or Fact? (Dental dose)
> 
> Dear RADSAFE subscribers,
> 
> I think that the entrance skin dose of 4.71 mGy is
> slightly high.
> 
> There are at least three recent survey reports as
> follows;
> UK survey: Napier, I.D. Reference doses for dental
> radiography.
>      British Dental Journal, 1999; 186: 392-396.
> US survey: Suleiman, O.H. et al. Radiographic trends
> of dental
>      offices and dental schools.
>      Journal of American Dental Association, 1999;
> 130: 1104-1110.
> Spain survey: Gonzalez, L, et al. Reference doses in
> dental
>      radiodiagnostic facilities.
>      The British Journal of Radiology, 2001; 74:
> 153-156.
> 
> UK and US survey reports are cited by the
> UNSCEAR2000 Report.
> 
> UK survey: The average entrance dose was 3.3 mGy,
> which included
>    the data at lower kV sets (45-55 kV). The average
> obtained at
>    kV sets commonly used (60-70 kV) was 2.2 mGy. The
> report
>    included much higher doses which I can not
> believe. The highest
>    at 60-70 kV sets was 20.5 mGy...
>    (Many years ago a professor in Sweden told me
> that the operation
>     at less than 60 kV is illegal in Sweden.)
> US survey: Mean entrance air kerma values ranged
> approx. between
>    1 mGy and 2 mGy. Sometimes X-ray equipments were
> operated at
>    higher kV settings in the United States.
> Spain survey: The mean value of skin doses was 2.89
> mGy.
> 
> If measurements are carried out at my school now,
> average entrance
> doses distribute approx. between 1 mGy and 2 mGy at
> 60-70 kV
> settings.
> 
> - - - - - -
> The record of dental doses in the 20th century was
> described by
> S.C. White, UCLA, in 1992 as follows;
> White SC. 1992 assessment of radiation risk from
> dental
> radiography.
> Dentomaxillofacial Radiology, 1992 Aug;
> 21(3):118-26.
> 
> Based on White's report, I can describe, "Doses with
> a single
> dental exposure (bitewing/intraoral radiography) are
> equivalent
> to between approx. 7 hours and 1 day background
> exposure.
> 
> - - - - - -
> A reasonable estimate in my opinion of the effective
> dose from
> a single dental (bitewing/intraoral) radiography
> ranges between
> 1 to 5 microSv (0.1 to 0.5 mrem). Another estimate
> in my opinion
> of the effective dose from the full mouth survey
> ranges between
> 10 to 50 microSv (1 to 5 mrem).
> 
> I agree the statement that in Europe a skilled
> dentist (or his
> technician) with state-of-the-art equipment will
> expose you to
> about 0.01 mSv effective dose per examination. But
> in a recent
> decade some sophisticated equipments have become
> world-wide
> available.
> 
> Now it can be said in my opinion, "Every year, the
> average
> globe citizen is exposed to natural radiation equal
> to about
> 720-3,600 dental X-rays."
> 
> Sincerely.
>    Yoshihiko Hayakawa
>    Tokyo Dental College
>     mailto:yhayaka at tdc.ac.jp
> 
> Peter Thomas wrote:
> 
> > New Zealand's NRL produced a report 15 years ago
> based on TLD
> > measurements in a RANDO phantom to get the ratio
> of organ doses to the
> > entrance skin dose for a couple of dental exams. 
> The following is for
> a
> > single bitewing film at 60kV based on an entrance
> skin dose of 4.71
> mGy
> > (471 mrad).  It's an old report but I'd expect
> similar results under
> > today's conditions given the same entrance skin
> dose.
> > 
> > Entrance skin  4.71 mGy
> > Ovaries 0.0000047 mGy
> > Testes 0.00044 mGy
> > Bone (in head/neck) 0.019 mGy
> > Breast 0.00196 mGy
> > Lungs 0.00106 mGy
> > Thyroid 0.0215 mGy
> > Brain 0.0094 mGy
> > Sinuses 0.426 mGy
> > Salivary Glands 0.275 mGy
> > Pharynx 0.327 mGy
> > Larynx 0.048 mGy
> > Liver 0.00011 mGy
> > Stomach 0.000052 mGy
> > Kidneys 0.000033 mGy
> > Small Intestine 0.000014 mGy
> > Eyeballs 0.021 mGy
> > 
> > The main contributors to the effective dose are
> the dose to the
> thyroid
> > and the dose to the salivary glands (0.025
> weighting factor under
> ICRP60
> > rules where a remainder tissue has a higher does
> than any of the
> tissues
> > with individual weighting factors).  The skin dose
> drops by a factor
> of
> > 600 due to the ratio of the irradiated area to
> that of the whole skin.
> > The bone dose gets mangled a bit by apportioning
> between bone surface
> > and bone marrow, enhancement factors and averaging
> over the whole body
> > and ends up contributing about 0.0005 mSv to the
> effective dose
> > 
> > Thyroid  0.05 x 0.02146 = 0.001 mSv
> > Salivary Glands 0.025 x 0.275 = 0.007 mSv
> > 
> > Effective Dose = 0.008 mSv (about 10 microSv or 1
> mrem)
> > 
> > Apologies for writing a lot of zeros.  I didn't
> want to have to write
> > 'micro' everywhere or cause confusion about what
> units I was using.
> > Hope I haven't made a transcription error.  In the
> original experiment
> > they set up an x-ray unit in its own room with a
> timer so they could
> > deliver the equivalent of about 10000 (ten
> thousand) exposures to poor
> > old RANDO.  The entrance skin dosimeters were
> removed part-way through
> > so the dose wouldn't be above 10 Gy and the final
> results were scaled
> > appropriately.  This is how they claim to be able
> to measure ratios
> 
=== message truncated ===

+++++++++++++++++++
>From an article about physicians doing clinical studies: 

"It was just before an early morning meeting, and I was really trying to get to the bagels, but I couldn't help overhearing a conversation between one of my statistical colleagues and a surgeon.

Statistician: "Oh, so you have already calculated the P value?"

Surgeon: "Yes, I used multinomial logistic regression."

Statistician: "Really? How did you come up with that?"

Surgeon: "Well, I tried each analysis on the SPSS drop-down menus, and that was the one that gave the smallest P value"."

-- John
John Jacobus, MS
Certified Health Physicist
e-mail:  crispy_bird at yahoo.com

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