Assessment of radiation exposure in dental cone-beam computerized tomography with the use of metal-oxide semiconductor field-effect transistor (MOSFET) dosimeters and Monte Carlo simulations

doi:10.1016/j.oooo.2012.06.003

Oral Surgery, Oral Medicine, Oral Pathology and Oral Radiology

Volume 114, Issue 3, September 2012, Pages 393-400

https://doi.org/10.1016/j.oooo.2012.06.003 Get rights and content

Objectives

The aims of this study were to assess the organ and effective dose (International Commission on Radiological Protection (ICRP) 103) resulting from dental cone-beam computerized tomography (CBCT) imaging using a novel metal-oxide semiconductor field-effect transistor (MOSFET) dosimeter device, and to assess the reliability of the MOSFET measurements by comparing the results with Monte Carlo PCXMC simulations.

Study Design

Organ dose measurements were performed using 20 MOSFET dosimeters that were embedded in the 8 most radiosensitive organs in the maxillofacial and neck area. The dose-area product (DAP) values attained from CBCT scans were used for PCXMC simulations. The acquired MOSFET doses were then compared with the Monte Carlo simulations.

Results

The effective dose measurements using MOSFET dosimeters yielded, using 0.5-cm steps, a value of 153 μSv and the PCXMC simulations resulted in a value of 136 μSv.

Conclusions

The MOSFET dosimeters placed in a head phantom gave results similar to Monte Carlo simulations. Minor vertical changes in the positioning of the phantom had a substantial affect on the overall effective dose. Therefore, the MOSFET dosimeters constitute a feasible method for dose assessment of CBCT units in the maxillofacial region.

Section snippets

Phantom

An anthropomorphic RANDO RAN102 male head phantom (Radiation Analogue Dosimetry System; Phantom Laboratory, Salem, NY, USA) was used for the dose measurements. The phantom comprises a human skull embedded in a soft tissue–equivalent material to match the attenuation and scattering conditions of the bone, soft tissues, and airways of the human head. The phantom consists of 10 25-mm-thick layers numbered from 0 to 9 in the order from the calvaria to the neck area (Figure 1). Each layer has a grid

MOSFET dose measurements

The imaging volume (dental area) used for the MOSFET dose measurements ranged from the tip of the chin to the sinuses (Z_ref 83 cm) and is shown in Figure 3.

The effective dose in the 8 × 8 cm FOV imaging volume using the standard clinical parameters (84 kV, 12 mA, 145 mAs) was 153 μSv. The major contributions (w_TH_T) to the effective dose originated from the remainder tissues (32%), salivary glands (21%), and thyroid gland (21%). The greatest contributors to the effective dose in the remainder

Discussion

A novel mobile MOSFET dosimetry device was used to determine organ and effective dose in the maxillofacial area using an anthropomorphic RANDO head phantom as the patient model. The purpose was also to compare the experimental MOSFET results with Monte Carlo simulations.

In an earlier study, Qu et al.²⁴ performed organ dose and effective dose measurements with the Promax 3D CBCT device using 8 × 8 cm FOV, 84 kV, 12 mA, 12 s, and 21 thermoluminescent dosimeters. Interestingly, our MOSFET

Conclusion

Taking into account the uncertainties in both systems, the MOSFET dosimeters placed in a RANDO phantom gave results similar to the Monte Carlo simulations. The MOSFET dosimeters constitute a feasible method for the dose assessment of CBCT units in the maxillofacial region and offer a very fast readout possibility compared with very time-consuming TLD sensors.

References (24)

R. Pauwels et al.
Effective dose range for dental cone beam computed tomography scanners
Eur J Radiol
(2012)
M. Loubele et al.
Comparison between effective radiation dose of CBCT and MSCT scanners for dentomaxillofacial applications
Eur J Radiol
(2009)
J.B. Ludlow et al.
Comparative dosimetry of dental CBCT devices and 64-slice CT for oral and maxillofacial radiology
Oral Surg Oral Med Oral Pathol Oral Radiol Endod
(2008)
X.M. Qu et al.
Effective radiation dose of promax 3D cone-beam computerized tomography scanner with different dental protocols
Oral Surg Oral Med Oral Pathol Oral Radiol Endontology
(2010)
J.B. Ludlow et al.
Dosimetry of two extraoral direct digital imaging devices: NewTom cone beam CT and Orthophos plus DS panoramic unit
Dentomaxillofac Radiol
(2003)
J.A. Roberts et al.
Effective dose from cone beam CT examinations in dentistry
Br J Radiol
(2009)
J.B. Ludlow et al.
Dosimetry of 3 CBCT units for oral and maxillofacial radiology
Dentomaxillofac Radiol
(2006)
A. Suomalainen et al.
Dosimetry and image quality of four dental cone beam computed tomography scanners compared with multislice computed tomography scanners
Dentomaxillofac Radiol
(2009)
Kim S, Sopko D, Toncheva G, Enterline D, Keijzers B, Yoshizumi TT. Radiation dose from 3D rotational x-ray imaging:...
N. Miksys et al.
Estimating effective dose to pediatric patients undergoing interventional radiology procedures using anthropomorphic phantoms and MOSFET dosimeters
AJR Am J Roentgenol
(2010)

S. Kim et al.

Radiation dose from cone beam CT in a pediatric phantom: risk estimation of cancer incidence

AJR Am J Roentgenol

(2010)

S. Kim et al.

Estimation of absorbed doses from paediatric cone-beam CT scans: MOSFET measurements and Monte Carlo simulations

Radiat Protect Dosim

(2010)

Cited by (41)

Impact of thyroid gland shielding on radiation doses in dental cone beam computed tomography with small and medium fields of view
2022, Oral Surgery, Oral Medicine, Oral Pathology and Oral Radiology
Citation Excerpt :
The phantom head was placed orthogonally to the detector plane of the CBCT unit and its position was confirmed by laser beams. To measure absorbed doses, 20 metal oxide semiconductor field-effect transistor (MOSFET) dosimeters (TN-RD-70-W20, Best Medical Canada, Ottawa, ON, Canada), calibrated at the Secondary Standard Dosimetry Laboratory, were positioned in the layers of the male phantom head in accordance with the protocol of Koivisto et al.36 (Table I). These positions represented organs and tissues known to be sensitive to radiation as listed in the International Commission on Radiological Protection (ICRP) Publication 103, issued in 200737 (Table II).
The purpose of this study was to evaluate the impact of thyroid gland shielding on radiation doses in dental cone beam computed tomography (CBCT) with small and medium fields of view (FOVs).
Six CBCT protocols were investigated by exposing an adult anthropomorphic male phantom head without and with thyroid shielding, using 4 small (4 × 5 cm) and 2 medium (10 × 6 cm) FOVs. Twenty metal oxide semiconductor field-effect transistor dosimeters were placed in the phantom head to measure absorbed doses and calculate equivalent doses at 11 sites. Effective doses were calculated based on the tissue weighting factors in International Commission on Radiological Protection Publication 103. The data were analyzed using the independent samples t test.
Thyroid gland shielding led to significant equivalent dose reductions in many tissues for all protocols. Equivalent dose reductions to the thyroid were significant in all 6 protocols (P ≤ .037). Significant reduction depended on the FOV and ranged between 24.5% and 42.6% for the thyroid gland and 4.9% and 34.5% for other tissues and organs. Effective doses were significantly lower in all protocols (P ≤ .016).
Thyroid gland shielding protects the thyroid gland and other organs and should be utilized with all CBCT examinations where feasible.
Dental cone beam CT: An updated review
2021, Physica Medica
Citation Excerpt :
Effective and organ doses have been determined using thermoluminescent dosimeters (TLD), optically stimulated luminescence (OSL) dosimeters, and metal–oxidesemiconductor field-effect transistor (MOSFET) detectors [53–55]. Recent studies have also used Monte Carlo simulations to estimate effective and organ doses [53,55–57]. The magnitudes of these biological dose quantities vary remarkably in dental CBCT depending on the FOV size, positioning, and exposure parameters.
Cone beam computed tomography (CBCT) is a diverse 3D x-ray imaging technique that has gained significant popularity in dental radiology in the last two decades. CBCT overcomes the limitations of traditional two-dimensional dental imaging and enables accurate depiction of multiplanar details of maxillofacial bony structures and surrounding soft tissues. In this review article, we provide an updated status on dental CBCT imaging and summarise the technical features of currently used CBCT scanner models, extending to recent developments in scanner technology, clinical aspects, and regulatory perspectives on dose optimisation, dosimetry, and diagnostic reference levels. We also consider the outlook of potential techniques along with issues that should be resolved in providing clinically more effective CBCT examinations that are optimised for the benefit of the patient.
Influence of patient position and other inherent factors on image quality in two different cone beam computed tomography (CBCT) devices
2017, European Journal of Radiology Open
The aim of this in vitro study was to evaluate how a deviation from the horizontal plane, affects the image quality in two different CBCT-devices.
A phantom head SK150 (RANDO, The Phantom Laboratory, Salem, NY, USA) was examined in two CBCT-units: Accuitomo 80 and Veraviewepocs 3D R100 (J. Morita Mfg. Corp. Kyoto, Japan). The phantom head was placed with the hard palate parallel to the horizontal plane and tilted 20 ° backwards. Exposures were performed with different field of views (FOVs), voxel sizes, slice thicknesses and exposure settings. Effective dose was calculated using PCXMC 2.0 (STUK, Helsinki, Finland). Image quality was assessed using contrast-to-noise-ratio (CNR). Region of interest (ROI) was set at three different levels of the mandibular bone and soft tissue, uni- and bilaterally in small and large FOVs, respectively. CNR values were calculated by CT-value and standard deviation for each ROI. Factor analysis was used to analyze the material.
Tilting the phantom head backwards rendered significantly higher mean CNR values regardless of FOV. The effective dose was lower in small than in large FOVs and varied to a larger extent between CBCT-devices in large FOVs.
Head position can affect the image quality. Tilting the head backward improved image quality in the mandibular region. However, if influenced by other variables e.g. motion artifacts in a clinical situation, remains to be further investigated.
Image quality assessed using CNR values to investigate the influence of different patient positions and FOVs.
Comparison of dosimetry methods for panoramic radiography: Thermoluminescent dosimeter measurement versus personal computer-based Monte Carlo method calculation
2016, Oral Surgery, Oral Medicine, Oral Pathology and Oral Radiology
The purpose of this study was to evaluate the patient radiation dose based on panoramic radiography and calculated with personal computer–based Monte Carlo (PCXMC) software compared with thermoluminescent dosimetry (TLD) measurement. We also proposed appropriate input values for dose-determining factors in PCXMC.
Tissue-absorbed doses and the effective dose based on panoramic radiography were measured with TLD and with PCXMC under various conditions. The calculated PCXMC doses were compared with those measured with TLD.
The effective doses calculated with PCXMC were higher by 9.55% to 51.24% compared with the doses measured with TLD. Reference points on the Y-axis and Z-axis were the sensitive factors when calculating the effective dose. The differences between the highest and the lowest organ doses were 0.32 and 0.10 mGy, respectively, for PCXMC calculation and TLD measurement.
The effective dose calculated with PCXMC was generally higher than the dose measured by using TLD, and the absorbed doses varied by organ more severely in the PCXMC calculations than in the TLD measurements. The effective dose obtained from PCXMC calculations was dependent on input values for dose-determining factors. Standard values for each dose-determining factor required for the application of PCXMC to panoramic radiography were suggested in this study.
Dental cone beam CT: A review
2015, Physica Medica
Citation Excerpt :
In addition to mammography, where organ doses are already implemented by mean glandular dose readings provided by modern digital mammography equipment [59–61], dental CBCT could be another modality driver of automatic organ dosimetry, as the X-ray beam in dental CBCT is applied to a relatively constant maxillofacial anatomy with a more certain delineation of exposed organ coverage. Morant et al. [62] and Koivisto et al. [40] have already proved the accuracy of Monte Carlo simulations for the dental organ dose evaluations. The MC code adapted to dental CBCT could provide an effective automatic tool for assessing patient specific organ doses in the future.
For the maxillofacial region, there are various indications that cannot be interpreted from 2D images and will benefit from multiplanar viewing. Dental cone beam CT (CBCT) utilises a cone- or pyramid-shaped X-ray beam using mostly flat-panel detectors for 3D image reconstruction with high spatial resolution. The vast increase in availability and amount of these CBCT devices offers many clinical benefits, and their ongoing development has potential to bring various new clinical applications for medical imaging. Additionally, there is also a need for high quality research and education. European guidelines promote the use of a medical physics expert for advice on radiation protection, patient dose optimisation, and equipment testing. In this review article, we perform a comparison of technical equipment based on manufacturer data, including scanner specific X-ray spectra, and describe issues concerning CBCT image reconstruction and image quality, and also address radiation dose issues, dosimetry, and optimisation. We also discuss clinical needs and what type of education users should have in order to operate CBCT systems safely. We will also take a look into the future and discuss the issues that still need to be solved.
Assessment of protocols in cone-beam CT with symmetric and asymmetric beams usingeffective dose and air kerma-area product
2015, Applied Radiation and Isotopes
This study aims to evaluate and compare protocols with similar purposes in a cone beam CT scanner using thermoluminescent dosimeter (TLD) and the air kerma-area product (P_KA) as the kerma index. The measurements were performed on two protocols used to obtain an image of the maxilla–mandible using the equipment GENDEX GXCB 500: Protocol [GX1] extended diameter and asymmetric beam (14 cm×8.5 cm-maxilla/mandible) and protocol [GX2] symmetrical beam (8.5 cm×8.5 cm-maxillary/mandible). LiF dosimeters inserted into a female anthropomorphic phantom were used. For both protocols, the value of P_KA was evaluated using a PTW Diamentor E2 meter and the multimeter Radcal Rapidose system. The results obtained for the effective dose/P_KA were separated by protocol image. [GX1]: 44.5 µSv/478 mGy cm²; [GX2]: 54.8 µSv/507 mGy cm². Although the ratio of the diameters (14 cm/8.5 cm)=1.65, the ratio of effective dose values (44.5 µSv/54.8 µSv)=0.81, that is, the effective dose of the protocol with extended diameter is 19% smaller. The P_KA values reveal very similar results between the two protocols. For the cases where the scanner uses an asymmetric beam to obtain images with large diameters that cover the entire face, there are advantages from the point of view of reducing the exposure of patients when compared to the use of symmetrical beam and/or to FOV images with a smaller diameter.

View all citing articles on Scopus

: This project was supported by Planmeca Oy. Juha Koivisto is an employee of Planmeca Oy.

View full text

Oral and maxillofacial radiologyAssessment of radiation exposure in dental cone-beam computerized tomography with the use of metal-oxide semiconductor field-effect transistor (MOSFET) dosimeters and Monte Carlo simulations

Objectives

Study Design

Results

Conclusions

Section snippets

Phantom

MOSFET dose measurements

Discussion

Conclusion

Eur J Radiol

Eur J Radiol

Oral Surg Oral Med Oral Pathol Oral Radiol Endod

Oral Surg Oral Med Oral Pathol Oral Radiol Endontology

Dosimetry of two extraoral direct digital imaging devices: NewTom cone beam CT and Orthophos plus DS panoramic unit

Dentomaxillofac Radiol

Effective dose from cone beam CT examinations in dentistry

Br J Radiol

Dosimetry of 3 CBCT units for oral and maxillofacial radiology

Dentomaxillofac Radiol

Dosimetry and image quality of four dental cone beam computed tomography scanners compared with multislice computed tomography scanners

Dentomaxillofac Radiol

Estimating effective dose to pediatric patients undergoing interventional radiology procedures using anthropomorphic phantoms and MOSFET dosimeters

AJR Am J Roentgenol

Radiation dose from cone beam CT in a pediatric phantom: risk estimation of cancer incidence

AJR Am J Roentgenol

Estimation of absorbed doses from paediatric cone-beam CT scans: MOSFET measurements and Monte Carlo simulations

Radiat Protect Dosim

Oral and maxillofacial radiology
Assessment of radiation exposure in dental cone-beam computerized tomography with the use of metal-oxide semiconductor field-effect transistor (MOSFET) dosimeters and Monte Carlo simulations