The value of thyroid shielding in intraoral radiography

Abstract

Objectives: To evaluate the utility of the application of a thyroid shield in intraoral radiography when using rectangular collimation. Methods: Experimental data were obtained by measuring the absorbed dose at the position of the thyroid gland in a RANDO ® (The Phantom Laboratory, Salem, NY) male phantom with a dosemeter. Four protocols were tested: round collimation and rectangular collimation, both with and without thyroid shield. Five exposure positions were deployed: upper incisor (Isup), upper canine (Csup), upper premolar (Psup), upper molar (Msup) and posterior bitewing (BW). Exposures were made with 70 kV and 7 mA and were repeated 10 times. The exposure times were as recommended for the exposure positions for the respective collimator type by the manufacturer for digital imaging. The data were statistically analyzed with a three-way ANOVA test. Significance was set at p , 0.01. Results: The ANOVA test revealed that the differences between mean doses of all protocols and geometries were statistically significant, p , 0.001. For the Isup, thyroid dose levels were comparable with both collimators at a level indicating primary beam exposure. Thyroid shield reduced this dose with circa 75%. For the Csup position, round collimation also revealed primary beam exposure, and thyroid shield yield was 70%. In Csup with rectangular collimation, the thyroid dose was reduced with a factor 4 compared with round collimation and thyroid shield yielded an additional 42% dose reduction. The thyroid dose levels for the Csup, Psup, Msup and BW exposures were lower with rectangular collimation without thyroid shield than with round collimation with thyroid shield. With rectangular collimation, the thyroid shield in Psup, Msup and BW reduced the dose 10% or less, where dose levels were already low, implying no clinical significance. Conclusions: For the exposures in the upper anterior region, thyroid shield results in an important dose reduction for the thyroid. For the other exposures, thyroid shield augments little to the reduction achieved by rectangular collimation. The use of thyroid shield is to be advised, when performing upper anterior radiography.

Are Bismuth Shields Useful in Dentomaxillofacial Radiology Practice for the Protection of Eyes and Thyroid Glands from Ionizing Radiation?

“…In dental practice, lead shielding has an important place to protect the thyroid gland and lens, and its effectiveness has been demonstrated by several studies (7,18,19). Hoogeveen et al (19) reported a dose reduction of 75% in the periapical exposures of upper anterior region using thyroid shielding and concluded that thyroid shielding results in significant thyroid dose reduction not only in the upper anterior region, but also in radiography of all upper teeth.…”

“…Hoogeveen et al (19) reported a dose reduction of 75% in the periapical exposures of upper anterior region using thyroid shielding and concluded that thyroid shielding results in significant thyroid dose reduction not only in the upper anterior region, but also in radiography of all upper teeth. Qu et al (7), who studied the effectiveness of thyroid collar shielding in different FOVs in CBCT scanning, found a reduction of 18% -40.1% with a single thyroid collar.…”

“…The dose received by this area is shown to be considerably reduced with the use of thyroid shielding (19). In this study, dose reduction in the thyroid region during the PR of upper anterior teeth obtained with bismuth shielding (63.90%) was lower in comparison to that obtained with lead shielding by Hoogeveen et al (75%) (19). This difference may be explained by the fact that bismuth shielding partially blocks the X-ray beam to the relevant area removing the low-energy photons.…”

The use of a thyroid shield for intraoral anterior oblique occlusal views—a risk-based approach

“…The medical physics expert will give their advice based in part on their understanding of the reduction in absorbed dose to the thyroid as a result of using a thyroid shield. Many studies have tried to quantify this; Sikorski and Taylor 11 for a full mouth intraoral series, Schmidt et al 12 for a periapical and Hoogeveen et al 13 for upper anterior views. Both Sikorski and Taylor 11 and Hoogeveen et al 13 suggested that thyroid shields should be used for the views they studied whilst Schmidt et al 12 suggested that thyroid shields were not a reasonable measure for the views they studied.…”

“…Many studies have tried to quantify this; Sikorski and Taylor 11 for a full mouth intraoral series, Schmidt et al 12 for a periapical and Hoogeveen et al 13 for upper anterior views. Both Sikorski and Taylor 11 and Hoogeveen et al 13 suggested that thyroid shields should be used for the views they studied whilst Schmidt et al 12 suggested that thyroid shields were not a reasonable measure for the views they studied. The authors cannot find any study that has explicitly investigated an anterior oblique occlusal view (also known as a standard occlusal view), although, Hoogeveen et al 13 did suggest that since their results indicated the use of a thyroid shield for upper anterior views this would be equally true of occlusal views.…”