comparison between absorbed doses in target organs in panoramic radiography, using single emulsion and double emulsion films

the use of panoramic radiography, due to its numerous advantages, is increasing. radiographic films used in this technique are of double emulsion (de) type which are used with intensifying screens. single emulsion (se) films can also be used. the purpose of this study was to determine the exposure parameters to achieve an appropriate optical density in these two types of films, and to estimate under such parameters, radiation doses to mandibular bone marrow (mbm), thyroid gland and parotid gland. this study was performed through a tissue equivalent phantom. first, with various tube voltage and tube current, 128 radiographs were taken of phantom with these two types of films. after examining the optical densities, the exposure parameters under which both films have the same density, were determined. then, phantom again was exposed and mbm, thyroid gland and parotid gland absorbed doses were measured, using tlds. it was demonstrated that: 1) se films, in order to provide appropriate optical density, require two times radiation in comparison with double emulsion film; 2) using se films increases mbm dose, up to 2-2.5 times, thyroid gland dose up to 1.7-2 times and parotid gland dose up to 1.3 times, in comparison with de films; 3) in de films, under lower exposure parameters and desirable processing, mbm dose up to 3.5 times, thyroid gland dose up to 1.5 times and parotid gland dose up to 2.5 times will increase. considering that the risk of radiation induced cancers increases with repeated radiation doses, using se films is not recommended.