Assessment of absorbed dose in critical organs in OPG: a phantom study

Orthopantomography is a well-established imaging technique in dental diagnosis. Although its exposure to individuals is relatively low compared to other diagnostic radiology examinations, it is still the most frequent X-ray examination. So it is important to estimate absorbed dose to critical organs in this examination. The present study was designed to determine the radiation doses to eyes, parotid, thyroid, submandibular gland and brain using Gafchromic films in an anthropomorphic head and neck phantom in three imaging centers, one digital and the remainders analogue. The absorbed dose to brain was measured globally with two vertically and horizontally embedded films in the phantom and submandibular, parotid and thyroid glands were also measured at their correct position in the phantom. The dose to the eyes was measured at the surface.Each measurement was triplicated and results were presented as mean (SD).After calibration of the films, they were embedded in the phantom and it was exposed with similar conditions for an adult patient. Absorbed doses were from 0.97-3.12 mGyfor brain, 1.23-3.02 mGy forleft parotid, 1.19-4.54 mGy for right parotid, 1.27-4.46 mGy left thyroid, 1.56-3.88 mGy for right thyroid, 1.45-2.83 mGy for Submandibular, 1.55-2.38 for right eye and 1.39-3.77 mGy for left eye.Our results showed similar depth and surface doses at all. Due to the direction of X-ray tube rotation, in the analogue devices in which the direction of rotation was right to left, doses of left sided organs were higher, and in the digital device that the direction was left to right, doses of right sided organs were higher. The absorbed doses in digital device were significantly lower than the analogue devices (p-value≤0.05).