Background: The anatomic position and proven radiosensitivity of the thyroid make it an
organ of concern in dental X-ray examinations. A National Radiation Protection Department
(NRPD)-sponsored pilot study carried out in the Dental Radiology Department of RUMS., to
assess if the radiation dose in panoramic radiographies could be reduced without significant
impairment of the subjective image quality.
Materials and Methods: Thermoluminescent dosimetry (TLD) is widely acknowledged to be
the recommended method for measuring entrance surface doses (ESD). In this study, ESD was
measured using LiF thermoluminescent dosimeters (TLD-100) on the thyroid of 40 patients
who had referred to the School of Dentistry, Rafsanjan University of Medical Sciences. Patients
were not exposed to any additional radiation and the radiographs were used for diagnostic
purposes. TLDs were calibrated with radiation energies similar to those commonly used in
orthopantomography.
Results: The overall mean ESD on the thyroid in orthopantomography was 0.071 ± 0.012 mGy
(ranged from 0.01 to 0.40 mGy). The mean ESD for radiographies performed with 66 kVp (20
patients) and 68 kVp (20 patients) were 0.072 ± 0.019, and 0.070 ± 0.016 respectively. No statistically
significant difference was found between these means.
Conclusions: The measured surface doses in our study are inconsistent with the only one
already reported about the same experiment. However, due to lack of national diagnostic reference
levels for orthopantomography, it is not clear whether in case of the PM 2002 CC unit used in
this experiment, reducing the radiation dose to a level that still keeps a diagnostically acceptable
image quality is necessary