Shika Hoshasen

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To promote optimization of radiation protection for patients in panoramic radiography, we surveyed dose-width products (DWPs) and dose-area products (DAPs) as standard patient dose metrics for adults at general dental offices in the Tokyo Bay area and compared the doses with the diagnostic reference level (DRL) recommended in the UK.
We measured the DWP in panoramic radiography with an array of thermo-luminescent dosimeter (TLD) tips set at the secondary slit. Reading values of the TLD were converted to air kermas using a pencil ionization chamber and a dosimeter, which were calibrated by the Japan Quality Assurance Organization. The height of the beam, H, at the secondary slit was also measured with an X-ray film, and then the DAP was calculated by the product of H and DWP.
The DWPs differed by a factor of 15 among 23 dental offices. As a whole, the DAPs showed good correlation with the DWPs. The DWPs for offices, at which adequate tube voltage and film/screen systems with a relative sensitivity higher than 400 were used, were less than 65 mGy mm of the DRL in the UK. The DWPs for offices using digital CCD systems were not necessarily less than the DRL. Offices with DWPs more than 65 mGy mm utilized film/screen systems with a sensitivity lower than 250 and old panoramic units with full-wave rectification. Offices with DWPs more than 100 mGy mm used X-ray beams wider than 10 mm at full width half maximum in dose profile. Offices with DWPs more than 200 mGy mm should check the slit alignment of the panoramic units as well as the developing process.
Of the dental offices surveyed, 57% showed DWPs less than 65 mGy mm of the DRL in panoramic radiography. Other offices with higher DWPs should confirm that the dose level is commensurate with the diagnostic purpose of the X-ray examination.

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