A peer-reviewed journal published by K. N. Toosi University of Technology

Bi₂O₃/silicone rubber composite thyroid shield in periapical radiography: Experimental and Monte Carlo assessment

Document Type : Research Article

Authors

1 Radiation Application Research School, Nuclear Science and Technology Research Institute (NSTRI), P.O. Box 3148643111, Karaj, Iran

2 Tehran University of Medical Sciences, Tehran, Iran

3 Department of Medical Radiation Engineering SR.C., Islamic Azad University, Tehran, Iran

4 Department of Nuclear Engineering, SR.C., Islamic Azad University, Tehran, Iran

Abstract
A thyroid shield composed of 70 wt% micro-sized Bi2O3 dispersed in a silicone rubber matrix was evaluated for radiation protection efficacy in periapical dental radiography. Absorbed dose to the thyroid gland was quantified using both Monte Carlo N-Particle (MCNP) simulations with a modified MIRD phantom and experimental measurements employing TLD-GR200 dosimeters positioned in the superior and inferior thyroid regions of a Rando anthropomorphic phantom. Irradiations were performed at 60 kV, 7 mA, and 0.32 s exposure time with a fixed 60° vertical angulation. Experimental results revealed thyroid absorbed doses of 72.7±25.7 µGy (unshielded), 40.9±15.6 µGy (commercial collar equivalent to 0.5 mm Pb), and 20.8±12.5 µGy (composite shield), corresponding to a 71.4% dose reduction with the composite shield, (compared to 43.7% for the commercial collar). Monte Carlo simulations at 60° angulation demonstrated dose reductions of 85.1% (commercial), and 83.3% (composite). Additionally, under SSDL inverse broad-beam conditions based on the IEC 61331-1 (RQR5, 70 kV), the composite shield achieved a 99.97% air kerma rate reduction, markedly superior to the 99.08% (commercial) and 98.13% (0.5 mm pure Pb). Although the composite shield exhibited superior shielding performance, its weight remains higher than commercial alternatives, indicating the need for further optimization.

Highlights

  • Bi2O3/SR composite thyroid collar (4 mm thick, 70 wt% Bi2O3) for periapical radiography.
  • Composite (mass thickness 1.072 g.cm−2) vs. commercial shield (0.5 mm Pb equivalent, mass thickness 0.714 g.cm−2).
  • TLD-GR200 measurements in Rando phantom: 71.4% thyroid dose reduction (composite) vs. 43.7% (commercial).
  • MCNP simulation at 60°: 85.1% dose reduction (commercial) vs. 83.3% (composite).
  • Superior shielding performance under broad-beam conditions (99.97% vs. 99.08% air kerma reduction).

Keywords


Copyright
RPE is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC 4.0).

Conflict of Interest
The authors declare no potential conflict of interest regarding the publication of this work‎.

Funding
‎The authors declare that no funds‎, ‎grants‎, ‎or other financial support were received during the preparation of this manuscript‎.

(2024). Thyroid collar standard. https://www.meddeal.in/91701-thyroid-collar-standard.html.
Aghaz, A., Faghihi, R., Mortazavi, S., et al. (2016). Radiation attenuation properties of shields containing micro and Nano WO3 in diagnostic X-ray energy range. International Journal of Radiation Research, 14:127.
Aghaz, A., Kardan, M., Deevband, M., et al. (2018). Comparison of two different methods for CTDIw calculation in CBCT systems. Iranian Journal of Medical Physics, 15:224–224.
Aghaz, A., Kardan, M., Deevband, M., et al. (2021). Patient- specific dose assessment using CBCT images and Monte Carlo calculations. Journal of Instrumentation, 16:P10011.
Al-Buriahi, M., Kavaz, E., Perianolu, U., et al. (2021). SrO effect on photon/particle radiation protection characteristics of SrO-PbO-B2O3 glasses. Journal of Inorganic and Organometallic Polymers and Materials, 31:4546–4562.
Alizadeh, M., Mohseni, M., Farhood, B., et al. (2022). Thermoluminescent characteristics of GR-200, TLD-700H and TLD-100 for low dose measurement: linearity, repeatability, dose rate and photon energy dependence. Journal of Biomedical Physics & Engineering, 12:111.
Ankerhold, U., Hupe, O., and Ambrosi, P. (2009). Deficiencies of active electronic radiation protection dosemeters in pulsed fields. Radiation Protection Dosimetry, 135:149–153.
Attix, F. (2008). Introduction to radiological physics and radiation dosimetry. John Wiley & Sons.
Aytugar, E., Kose, T., Gumru, B., et al. (2018). Are bismuth shields useful in dentomaxillofacial radiology practice for the protection of eyes and thyroid glands from ionizing radiation? Iranian Journal of Radiology, 15.
Bawazeer, O., Almutairi, H., Almutiri, K., et al. (2024). Radiation protection in dental imaging: Evaluating the impact of the SABA thyroid shield during panoramic and cone beam computed tomography. Journal of Radiation Research and Applied Sciences, 17:101102.
Berger, M. and Hubbell, J. (1987). XCOM: Photon cross sections on a personal computer. Technical report, National Bureau of Standards, Washington, DC (USA). Center for Radiation.
Berger, M., Hubbell, J., Seltzer, S., et al. (2010). XCOM: Photon Cross Section Database. Technical report, National Institute of Standards and Technology, Gaithersburg, MD.
Charles, M. (2010). Effects of Ionizing Radiation: United Nations Scientific Committee on the Effects of Atomic Radiation: UNSCEAR 2006 Report, Volume 1Report to the General Assembly, with Scientific Annexes A and B. Oxford University Press.
Demir, L., Perianolu, U., and ahin, M. (2019). Investigating XRF parameters and valance electronic structure of the Co, Ni, and Cu spinel ferrites. Ceramics International, 45:7748–7753.
Demirel, and Ycel, H. (2024). Development of a flexible composite based on vulcanized silicon casting with bismuth oxide and characterization of its radiation shielding effectiveness in diagnostic X-ray energy range and medium gamma-ray energies. Nuclear Engineering and Technology, 56:2570–2575.
Eder, H. and Schlattl, H. (2018). IEC 61331-1: A new setup for testing lead free X-ray protective clothing. Physica Medica, 45:6–11.
Einstein, A., Elliston, C., Groves, D., et al. (2012). Effect of bismuth breast shielding on radiation dose and image quality in coronary CT angiography. Journal of Nuclear Cardiology, 19:100–108.
Gholamzadeh, L., Asari-Shik, N., Aminian, M., et al. (2020). A study of the shielding performance of fibers coated with high-Z oxides against ionizing radiations.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 973:164174.
Hafezi, L., Arianezhad, S., and Pooya, S. H. (2018). Evaluation of the radiation dose in the thyroid gland using different protective collars in panoramic imaging. Dentomaxillofacial Radiology, 47:20170428.
Hakanen, A., Kosunen, A., Pyry, P., et al. (2007). Determination of conversion factors from air kerma to operational dose equivalent quantities for low-energy X-ray spectra. Radiation Protection Dosimetry, 125:198–204.
Han, E., Bolch, W., and Eckerman, K. (2006). Revisions to the ORNL series of adult and pediatric computational phantoms for use with the MIRD schema. Health Physics, 90:337–356.
Hoogeveen, R., Hazenoot, B., Sanderink, G., et al. (2016). The value of thyroid shielding in intraoral radiography. Dentomaxillofacial Radiology, 45:20150407.
Hosseini, M., Malekie, S., and Kazemi, F. (2022). Experimental evaluation of gamma radiation shielding characteristics of Polyvinyl Alcohol/Tungsten oxide composite: A comparison study of micro and nano sizes of the fillers. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1026:166214.
IAEA (2018). Occupational Radiation Protection, IAEA Safety Standards Series No. GSG-7. IAEA, Vienna.
IEC (2005). IEC 61267, Medical diagnostic X-ray equipment-Radiation conditions for use in the determination of characteristic. Technical report, International Electrotechnical Commission.
IEC 61331-1 (2014). Protective devices against diagnostic medical X-radiation - Part 1: Determination of attenuation properties of materials. Technical report, International Electrotechnical Commission.
IEC 61331-3 (2014). Protective devices against diagnostic medical X-radiation - Part 3: Protective clothing, eyewear and protective patient shields. Technical report, International Electrotechnical Commission.
ISO/IEC Guide 98-3:2008 (2008). Uncertainty of measurement - Part 3: Guide to the expression of uncertainty in measurement (GUM:1995). ISO and IEC.
Janani, K., Malarkodi, T., and Sankarapandian, S. (2021). Estimation of Surface Radiation Dosage to Thyroid Gland and Lower Abdomen While Using Intraoral Periapical Radiography: A Phantom Study. Cureus, 13.
Jayakumar, S., Saravanan, T., and Philip, J. (2023). A review on polymer nanocomposites as lead-free materials for diagnostic X-ray shielding: Recent advances, challenges and future perspectives. Hybrid Advances, page 100100.
Kelaranta, A., Ekholm, M., Toroi, P., et al. (2016). Radiation exposure to foetus and breasts from dental X-ray examinations: effect of lead shields. Dentomaxillofacial Radiology, 45:20150095.
Kim, S., Frush, D., Yoshizumi, T., et al. (2010). Pediatric Radiology, 40:1739–1743.
Knoll, G. (2010). Radiation Detection and Measurement. John Wiley & Sons, Inc, 4th edition.
Lee, Y., t. Park, E., Cho, P., et al. (2011). Comparative analysis of radiation dose and image quality between thyroid shielding and unshielding during CT examination of the neck. American Journal of Roentgenology, 196:611–615.
Ludlow, J., Davies-Ludlow, L., and White, S. (2008). Patient risk related to common dental radiographic examinations: the impact of 2007 International Commission on Radiological Protection recommendations regarding dose calculation. The journal of the American Dental association, 139:1237–1243.
Maeda, T., Hayashi, H., Lee, C., et al. (2022). Experimental study of X-ray dose reduction factor when using various size bismuth and lead particles. Radiation Physics and Chemistry, 195:110049.
Malekie, S., Shooli, H., and Hosseini, M. (2022). Assessment of new composites containing polyamide-6 and lead monoxide as shields against ionizing photonic radiation based on computational and experimental methods. Scientific Reports, 12:1–15.
Mehrara, R., Malekie, S., Kotahi, S. S., et al. (2021). Introducing a novel low energy gamma ray shield utilizing Polycarbonate Bismuth Oxide composite. Scientific Reports, 11:10614.
Mishra, I., Karjodkar, F., Sansare, K., et al. (2018). Diagnostic value of extraoral periapical radiograph in comparison to intraoral periapical radiograph: a cross-sectional, institutional study. Contemporary Clinical Dentistry, 9:406–409.
Moafi, M., Geraily, G., Shirazi, A., et al. (2015). Analysis of TLD-100 calibration and Correction factor in different field sizes under low dose conditions irradiated with two systems: Gamma knife 4C and Theratron 780-C. Frontiers in Biomedical Technologies, 2:227–236.
More, C., Alsayed, Z., Badawi, M., et al. (2021). Polymeric composite materials for radiation shielding: a review. Environmental Chemistry Letters, pages 1–34.
Mortazavi, S., Faghihi, R., Aghamiri, M., et al. (2013). New Challenges in Moving Toward Nano-Sized Lead-Free Radiation Shields. Medical Physics, 1:254.
Nair, M. and Nair, U. (2007). Digital and advanced imaging in endodontics: a review. Journal of endodontics, 33:1–6.
National Council on Radiation Protection and Measurements (2003). Radiation protection in dentistry: recommendations of the National Council on Radiation Protection and Measurements. National Council on Radiation Protection and Measurements, Bethesda.
Navab, M., Hosseini, P., Afarideh, H., et al. (2016). Response of TLD and RPL personal dosimeters in a national intercomparison test program.
Park, S., Lee, J., and Lee, C. (2006). Development of a Korean adult male computational phantom for internal dosimetry calculation. Radiation protection dosimetry, 121:257–264.
Pooya, S. and Orouji, T. (2014). Evaluation of effective sources in uncertainty measurements of personal dosimetry by a Harshaw TLD system. Journal of Biomedical Physics & Engineering, 4:43.
Qu, X., Li, G., Zhang, Z., et al. (2012). Thyroid shields for radiation dose reduction during cone beam computed tomography scanning for different oral and maxillofacial regions. European journal of radiology, 81:e376–e380.
Sadeghi, B., Imani, R. P., Kiani, H., et al. (2025). Comparison of the Measurement Uncertainty of Thermoluminescence Dosimeters (TLD-100 and GR-200) in Clinical Radiotherapy Energies. Journal of Biomedical Physics and Engineering.
Shahbazi, L., Sardari, D., Malekie, S., et al. (2026). Evaluation of a flexible thyroid shield in dental panoramic radiography utilizing bismuth oxide silicone rubber composite and Rando phantom. Scientific Reports, 16:541.
Srinivasan, K. and Samuel, E. (2017). Evaluation of radiation shielding properties of the polyvinyl alcohol/iron oxide polymer composite. Journal of medical physics, 42:273.
Takegami, K., Hayashi, H., Maeda, T., et al. (2023). Thyroid dose reduction shield with the generation of less artifacts used for fast chest CT examination. Radiation Physics and Chemistry, 203:110635.
Ufuk, P., Alm, B., Mine, U., et al. (2016). Effect of external magnetic field on the K/K X-ray intensity ratios of TixNi1-x alloys excited by 59.54 and 22.69 keV photons.
Urtekin, E., Perianolu, U., Demir, L., et al. (2020). Investigating photon interaction characteristics of FexNi1-x alloys. Materials Chemistry and Physics, 242:122505.
Vollmar, S. and Kalender, W. (2008). Reduction of dose to the female breast in thoracic CT: a comparison of standard-protocol, bismuth-shielded, partial and tube- current-modulated CT examinations. European radiology, 18:1674–1682.
Worrall, M., Menhinick, A., and Thomson, D. (2018). The use of a thyroid shield for intraoral anterior oblique occlusal views a risk-based approach. Dentomaxillofacial Radiology, 47:20170140.
Volume 7, Issue 3
Summer 2026
Pages 75-88

  • Receive Date 15 February 2026
  • Revise Date 20 June 2026
  • Accept Date 27 June 2026