Abstract
Chest X-ray imaging is the most common X-ray imaging method for diagnosing coronavirus disease. The thyroid gland is one of the most radiation-sensitive organs of the body, particularly in infants and children. Therefore, it must be protected during chest X-ray imaging. Yet, because it has benefits and drawbacks, using a thyroid shield as protection during chest X-ray imaging is still up for debate.Therefore, this study aims to clarify the need for using a protective thyroid shield during chest X-ray imaging. This study was performed using different dosimeters (silica beads as a thermoluminescent dosimeter and an optically stimulated luminance dosimeter) embedded in an adult male ATOM dosimetric phantom. The phantom was irradiated using a portable X-ray machine with and without thyroid shielding. The dosimeter readings indicated that a thyroid shield reduced the radiation dose to the thyroid gland by 69% ± 18% without degrading the obtained radiograph. The use of a protective thyroid shield during chest X-ray imaging is recommended because its benefits outweigh the risks.
Keywords: Chest X-ray, Shielding, Thyroid region, Radiation protection, Dosimetry, Optically stimulated luminance
1. Introduction
The thyroid gland is one of the most radiation-sensitive organs in the human body, particularly in infants and children. It absorbs available iodine in the bloodstream to produce hormones that regulate the body's energy and metabolism. Therefore, it must be protected during chest radiographs (Sinnott et al., 2010). The density of the X-ray shielding material is the most crucial factor in radiation protection. Lead aprons and blankets are considered the most effective X- and gamma-ray shielding materials. A lead apron is effective when worn appropriately and utilised in a safe and routinely examined environment (Matsuda and Suzuki, 2016). Two main strategies generally adopted for reducing the radiation exposure of radiologists and related staff are (1) safeguarding through the use of shielding materials and (2) reduction of X-ray exposure as per the As Low As Reasonably Achievable (ALARA) rule. Safeguarding is primarily accomplished using 0.25- or 0.5-mm-thick lead shielding covers that respectively reduce the radiation exposure by more than 90% or ∼100% (Hyun et al., 2016). The objective of protection through the reduction of radiation exposure is to dependably prevent the deterministic impacts of radiation and to reduce the danger of stochastic impacts at all feasible levels (Le Heron et al., 2010; Hiles et al., 2021).
Chest X-ray imaging is the most common X-ray imaging method performed, particularly for diagnosing coronavirus disease (Yasin and Gouda, 2020). The use of lead aprons as shields during chest X-ray imaging remains debatable because it has certain benefits as well as some risks. Specifically, during erect chest X-ray imaging, a lead apron is routinely placed behind the patient to protect the genitals and reduce exposure from tube leakage and room scatter. However, the protective effect of lead aprons may be negligible, considering that the leakage from these sources is not measurable in current chest X-ray imaging rooms (Karami et al., 2016). In addition, using lead aprons during chest X-ray imaging may produce an artifact in the radiograph. Even clinical and medical groups, including the American Association of Physicists for Medication and the American College of Radiology, have suggested that using lead aprons may reduce the accuracy of imaging tests and incidentally increase the radiation exposure of patients. However, using a lead apron remains advisable because its benefits outweigh the risks (Marsh and Silosky, 2019).
This study investigates the benefits and risks of using a lead apron to protect the thyroid gland during chest X-ray imaging. For this purpose, different dosimeters, including silica beads as a thermoluminescent dosimeter (TLD) and an optically stimulated luminance (OSL) dosimeter, were embedded in adult dosimetric phantoms, and radiation exposure is performed using a portable X-ray machine with and without thyroid shielding.
2. Materials and methods
A portable X-ray machine is a smaller, more portable version of a conventional X-ray machine. It enables radiographers to take X-ray images with various exposure parameters without requiring patients to enter a lead-lined room. A Siemens MOBILETT XP portable X-ray machine was used at 85 kV and 1 mAs to acquire a chest radiograph.
In radiology, phantoms are used to estimate the radiation dose delivered to patients and evaluate the quality of the imaging systems. Therefore, the phantom should be composed of a material that closely mimics human tissue, particularly in terms of radiological characteristics. The advantages of using a phantom are that it is easily obtainable, provides more consistent results than those obtained with a subject, and avoids radiation-related risks to a subject. Fig. 1 shows the ATOM dosimetric phantom used in the study.
Fig. 1.
ATOM dosimetric phantom used in procedure.
A thyroid shield is used as a precautionary measure against radiation exposure. Radiation assurance protocols require the use of a thyroid shield. Thyroid collars safeguard all regions in danger and offer a completely flexible fit, making them simple to wear all day and in different manners.
The Inlight dosimetry system uses an OSL reader to provide users with reliable and accurate radiation monitoring. The radiation dose is measured using carbon-doped aluminium oxide detectors and is read out by the OSL reader.
3. Results
Table 1, Table 2 indicate that the “highest exposure” reading is obtained when the dosimeter is placed outside the phantom and in the direct X-ray beam, and the “background” reading is the reading obtained without irradiating the dosimeter.
Table 1.
Results of TLD experiment.
| TLD number | Dose (mGy) | |
|---|---|---|
| 1 | 0.19 | Background |
| 2 | 0.51 | Highest exposure |
| 3 | 0.29 | Without shield |
| 4 | 0.22 | |
| 5 | 0.20 | |
| 6 | 0.29 | |
| 7 | 0.36 | |
| 8 | 0.24 | |
| 9 | 0.15 | With shield |
| 10 | 0.19 | |
| 11 | 0.34 | |
| 12 | 0.30 |
Table 2.
Results of OSL experiment.
| OSL Number | Dose (mGy) | OSL Number | Dose (mGy) |
|---|---|---|---|
| 1 (Background) | 0.021 | 2 (Highest exposure) | 0.416 |
| Dose without shield (mGy) | Dose with shield (mGy) | ||
| 3 | 0.295 | 11 | 0.047 |
| 4 | 0.307 | 12 | 0.053 |
| 5 | 0.364 | 13 | 0.049 |
| 6 | 0.305 | 14 | 0.060 |
| 7 | 0.206 | 15 | 0.095 |
| 8 | 0.284 | 16 | 0.076 |
| 9 | 0.203 | 17 | 0.102 |
| 10 | 0.185 | 18 | 0.115 |
In the first experiment, the portable X-ray machine was used to provide radiation exposure to the phantom, and the TLD data were read out using the reader. Table 1 lists the TLD results at different positions (Fig. 2 ). However, TLD experiment was not repeated for accuracy and repeatability because TLD chips were broken during reading.
Fig. 2.
Simulation of phantom with TLD positions inside it. Green numbers indicate TLDs with shield. Pink numbers indicate TLDs without shield.
In the second experiment, the OSL data were read out using the reader. Table 2 lists the OSL results at different positions; OSL dosimeters in the same row had the same position, as illustrated in Fig. 3 .
Fig. 3.
Simulation of phantom with OSL positions inside it. Green numbers indicate TLDs without shield. Pink numbers indicate TLDs with shield.
4. Discussion
The results indicate that in the absence of shielding, a larger chest area was exposed to radiation than that with shielding. Specifically, the neck tissue was more exposed in the absence of a thyroid shield, resulting in a more damaging radiation effect. As noted above, experiments were performed with TLD chips and with OSL. The results indicated that TLD chips broke and, consequently, provided inaccurate readings; therefore, the OSL strategy was superior to the TLD method.
Furthermore, the amount of radiation exposure measured for chest radiography herein agrees with the results reported by Han et al. (2013), indicating that the use of the thyroid shield reduces the radiation dose (Han et al., 2013). Specifically, the results of the present study indicated that using the thyroid shield during chest X-ray imaging significantly reduced the effective radiation dose by 69% ± 18%, which is consistent with a previous report of a 72% reduction in radiation exposure (Karami et al., 2016). Another study indicated that the dosage amount decreased by only 47% in the thyroid region, and half of the reduction was attributable to the use of the thyroid shield (Hohl et al., 2006).
Overall, the results indicate that the thyroid shield is crucial in protecting the thyroid region from unwanted radiation exposure.
5. Conclusion and recommendations
This study aimed to clarify the effectiveness of a thyroid shield in protecting the thyroid gland from radiation exposure. For this purpose, different dosimeters were tested, including silica beads as a TLD and an OSL dosimeter. However, the results obtained using silica beads were not considered because the TLD reader was inefficient. Overall, the results indicated that the thyroid shield significantly reduced radiation exposure to the thyroid gland by 69% ± 18% without degrading the chest radiograph. Therefore, the thyroid shield should be used to protect the thyroid region from unwanted radiation exposure, and its benefits exceed its risks.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
We would like to thank Editage (www.editage.com) for English language editing.
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Handling Editor: Dr. Chris Chantler
Data availability
Data will be made available on request.
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Associated Data
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Data Availability Statement
Data will be made available on request.