Dose reduction of cone beam CT scanning for the entire oral and maxillofacial regions with thyroid collars

Abstract

Objective: The aim of this study was to evaluate the influence of thyroid collars on radiation dose during cone beam CT (CBCT) scanning. Methods: Average tissue-absorbed dose for a NewTom 9000 CBCT scanner (Quantitative Radiology, Verona, Italy) was measured using thermoluminescent dosemeter chips in a phantom. The scans were carried out with and without thyroid collars. Effective organ dose and total effective dose were derived using International Commission on Radiological Protection 2007 recommendations. Results: The effective organ doses for the thyroid gland and oesophagus were 31.0 mSv and 2.4 mSv, respectively, during CBCT scanning without a collar around the neck. When the thyroid collars were used loosely around the neck, no effective organ dose reduction was observed. When one thyroid collar was used tightly on the front of the neck, the effective organ dose for the thyroid gland and oesophagus were reduced to 15.9 mSv (48.7% reduction) and 1.4 mSv (41.7% reduction), respectively. Similar organ dose reduction (46.5% and 41.7%) was achieved when CBCT scanning was performed with two collars tightly on the front and back of the neck. However, the differences to the total effective dose were not significant among the scans with and without collars around the neck (p 5 0.775). Conclusions: Thyroid collars can effectively reduce the radiation dose to the thyroid and oesophagus if used appropriately.

Effectiveness of thyroid gland shielding in dental CBCT using a paediatric anthropomorphic phantom

“…Therefore, leadequivalent and lead thyroid shields are as effective as each other in CBCT imaging. Studies in adult phantoms have shown 0.35-mm lead equivalence is most effective; 18,19 however, this was the only thickness of thyroid shield tested. The better performance of Design 2 for the superior slice may have been owing to a better neck adjustment, and the lateral aspects of the neck are shielded using this design, since the neck straps also contain shielding materials.…”

“…Adult dosimetry laboratory studies have shown a dose reduction ranging from 44% to 72%. 18,19,27 The average thyroid dose can be compared with the study by Theodorakou et al, 11 since a similar phantom, same machine, exposure factors and FOV were used. The average thyroid dose obtained without a thyroid shield was higher than that recorded by Theodorakou et al 11 This difference may be explained by the different location of the TLDs.…”

“…Studies performed to date have used adult phantoms where the position of the thyroid gland is well known. Several dosimetric studies 1,7,18,19 used the positioning of TLDs in the head and neck region of an adult phantom described in the Ludlow et al 4 study. The position and shape of the thyroid gland in a paediatric phantom was determined by analysis of patients' images.…”

“…18,19 A simple strategy when positioning the patient during CBCT examination is to tilt the mandible upwards extending the neck, so the exposure to the thyroid gland is reduced by the increased distance of the beam and the gland. This strategy has been proved to be effective in dental CBCT and medical CT. 3,25 However, such a manoeuvre is not possible in a laboratory study using rigid anthropomorphic phantoms.…”

The Image Gently in Dentistry campaign: promotion of responsible use of maxillofacial radiology in dentistry for children

“…33 Protective thyroid collars are recommended for both dental intraoral and CBCT radiographic procedures, because their use reduces radiation exposure to the thyroid gland by about 50%. [34][35][36] Leaded aprons should include thyroid collars.…”