Radiation Doses in Dental Panoramic Tomography

Dental panoramic tomography is a technique by which an image of the entire dentition may be obtained on a single film, without superimposition of superficial structures or deeper than teeth and jaws. These machines are characterized by the fact that the tube and the cassette holder are mobile, so they rotate from one side of the patient’s head around his back to the other side. During this motion the film cassette moves in a synchronic way producing a two-dimensional image of the entire curved jaw with orthogonal projections of the teeth. The x-ray scanning movement generates a complex dose distribution with very different values in dose points, so skin dose is not a good indicator to estimate radiological risk in this case. Effective dose, dose-area product and imparted energy are the most suitable quantities to assess the risk of cancer disease associated with the exposure. The aim of this study is to get exposure distribution, skin dose, absorbed doses in organs and effective dose with a Gendex Orthoralix SD2 machine, using an anthropomorphic phantom loaded with lithium fluoride thermoluminiscence dosemeters. The obtained value of skin dose in the occipital region is similar to the published by other authors that have used phantoms. However, this value is less than estimated skin doses in real patients and reference values that those proposed in other papers. The value of effective dose was found to be less than the published ones by other authors, since the measured absorbed dose in thyroid was very low. Although the effective dose is usually a good indicator to assess the radiological risk, this estimation with anthropomorphic phantoms in head and neck surveys is not very accurate, owing to the intrinsic uncertainty of the method, the low irradiation of the most radiosensitive organs and the high contribution of thyroid to the effective dose.