Evaluation of a flexible thyroid shield in dental panoramic radiography utilizing bismuth oxide silicone rubber composite and Rando phantom

Initially, micro and nano bismuth oxide/ silicone rubber (Bi₂O₃/SR) composites at concentration of 70 wt% were fabricated. Analyses including XRD, SEM, EDS-Map, and TGA were performed on the samples, which indicated the dispersion of bismuth oxide micro and nano particles in the polymer matrix. Subsequently, the initial irradiation tests of the samples were performed by X-ray tube 60 kV at the SSDL of Iran. Results showed that there was no significant difference between the shielding effectiveness of micro and nano composites at 70 wt%. Therefore, in the final phase, considering economic considerations, a thyroid shield with a strap length of 58 cm, width of 23 cm, strap width of 6.4 cm, and length of 14 cm with thickness of 4 mm was manufactured using micro particles of Bi₂O₃ in the SR matrix. Then, radiation tests of the composite thyroid shield were conducted in an Orthopantomogram (OPG) radiology using the TLD-GR200 dosimeters and head-neck part of an adult male Rando phantom at 75 kV, 13 mA, with exposure time of 14.1 s. Results reveal that the thyroid gland received an absorbed dose of 386.6 ± 219.8 µSv, 19.0 ± 12.4 µSv, and 37.9 ± 18.7 µSv for unshielded, composite shield, and commercial thyroid collar (equivalent to 0.5 mm Pb), respectively. This shows a 95.1% reduction in dose with composite shielding, which is 5.4% more effective than commercial thyroid collar.