[ RadSafe ] Myth or Fact? (Dental dose)

Sat Aug 26 16:35:24 CDT 2006

Dental entrance air kerma values should be ~ 1 mGy.

The data we published in 1999 in JADA was derived from the Nationwide Evaluation of X-ray Trends (NEXT) survey program, an ongoing survey program among the US states and federal Food and Drug Administration.  Organizations such as the American College of Radiology also help fund the program.

This data, collected using patient equivalent phantoms, for standardization purposes, is repeated every few years for 6 or 7 routine diagnostic exams (dental, mammography, chest, abdomen (L/S spine), fluoroscopy, CT, and pediatric exams.  Go to www.crcpd.org (Conference of radiation Control Program Directors) for access to this data. You may have to search for it (have not visited there lately- but check out "publications") Although dental entrance air kerma values (free in air)  average about 1 mgy, the value is highly related to kVp, the lower the kVp, the higher the entrance air kerma (ESE - mR).)

~1 mGy seem to be the mean (I don't memorize the data), and the dose has been going down for several reasons, faster speed films, digital doses are also lower (compared to non-screen direct exposure film), and some states actually test the fim processing using standard sensitometers and film traceable to properly operating processors.

I think there has been a more recent dental survey.

-------------- Original message -------------- 
From: Yoshihiko Hayakawa <yhayaka at tdc.ac.jp> 

> 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 down 
> > to about 1 in a million (ovaries/entrance surface). 
> > 
> > The original report is: 
> > B D P Williamson, NRL 1990/6 
> > 
> > End result (apologies for the bandwidth): 10 microSv or 1 mrem 
> > (effective dose) is a reasonable estimate in my opinion of the dose from 
> > a single dental x-ray. 
> > 
> > Peter Thomas 
> > Medical Physics Section 
> > ARPANSA 
> > 
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