Evaluation of the radiation dose from dental cone-beam computed tomography: short communication

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BACKGROUND

Numerous studies have been conducted on cone-beam computed tomography (CBCT) scanners to calculate the radiation dose received by subjects [1–3]. Most of these studies have used thermoluminescence dosimeters (TLDs) placed within phantoms composed of tissue-equivalent materials to evaluate standard patient doses [4–6]. In 1998, CBCT was introduced in dentistry by Mozzo et al. [7]. CBCT generates three-dimensional (3D) images of the head and neck and is utilized in various dental fields, including dental surgery, endodontics, trauma, implant dentistry, soft tissue lesions and diseases in the head and neck, and orthodontics [8–10]. CBCT has become one of the most essential and effective tools in oral and maxillofacial diagnosis, treatment planning, and radiation therapy [11–13]. CBCT examinations involve a higher radiation dose than conventional panoramic imaging but a lower dose than conventional CT scanning [1, 13]. Dental radiologists often prefer CBCT over CT scanning due to its advantages, including superior image quality, affordability, compact size, availability, and lower radiation dose. In addition, CBCT is more suitable for dentists to acquire and analyze images, and it offers greater patient comfort due to technological advancements [3, 14, 15]. However, the examination dose of CBCT depends on the system configuration and radiation protocol [16]. CBCT offers various field of views (FOVs) options and VOX size settings that are suitable for dental examinations. Large, medium, and small FOVs produce volumes sufficient for imaging the maxillofacial region, dentoalveoli, and localized areas, respectively [17, 18]. The radiation field in dental imaging includes the head and neck region, encompassing the eyes, thyroid gland, and salivary glands [19–21]. Therefore, it is important to minimize the CBCT radiation dose patients receive, due to associated radiological hazards [5, 10, 22]. However, image quality should remain optimal even when the radiation dose is reduced [20, 21].

AIM

To evaluate the seven tissue doses using three scan protocols on a cone-beam computed tomography scanner KaVo OP 3D Pro, and to investigate the effect of resolution options on the effective dose.

METHODS

Study Design

It was an experimental (in vitro), single-center study.

Cone-beam Computed Tomography

The cone-beam computed tomography (CBCT) scanner used in this study was the (KaVo ORTHOPANTOMOGRAPH (OP) 3D Pro CBCT scanner Germany). As shown in Table 1 protocol-1, protocol-2 and protocol-3 used the same field of view (13 cm × 15 cm), which encompasses most of the maxillofacial region. The resolution settings for protocol 1, protocol 2 and protocol 3 were low resolution (420 μm voxel size), standard resolution (380 μm voxel size), and high resolution (320 μm voxel size), respectively. Therefore, a smaller voxel size corresponds to higher resolution, albeit with a lower tube current.

 

Table 1. Parameters of the cone-beam computed tomography (CBCT) scan protocols used in the study
Parameter	Protocols
	1	2	3
Voxel size (μm)	420	380	320
FOV (cm)	13×15	13×15	13×15
Tube voltage (kV)	90	90	90
Tube current (mA)	3.2	5	8
Exposure time (s)	4.5	8.1	8.1
Resolution	Low	Standard	High
Application	Orthodontic and Initial Assessments	General dentistry and routine examinations	Implant planning, endodontic, periodontal

 

A single model of tomography was used due to practical considerations, such as the availability of equipment within the institution and a focus on utilizing existing resources, allowing detailed exploration of one single model.

The methodological advantages include consistency through standardized image quality; optimization for better understanding and refinement; improved reliability by reducing variability in diagnostic interpretations. In addition, cost-effectiveness by minimizing equipment and training expenses, development of specialized expertise and, a streamlined workflow due to familiarity with the system.

The scanning range of the CBCT protocols used in this study included the following: X-ray source (90 kVp, 5–100 mA), detector (CMOS (Complementary Metal-Oxide-Semiconductor) flat-panel), voxel size (420 μm, 380 μm, and 320 μm), field of view (FOV), (13 cm × 15 cm), scan time (8–27 seconds), and dose range (50–350 μSv).

The software and integration used in this study included KaVo OP 3D imaging software, DICOM (Digital Imaging and Communications in Medicine) compatibility, and integration with dental software (e.g., OrthoAnalyzer, Implant Planning Software).

Measurement of Absorbed and Effective Doses

Radiation exposure measurements were conducted using TLD-100 (LiF) dosimeters. They were placed in a sealed plastic beaker and fixed within a human phantom, as shown in Fig. 1. A total of 63 dosimeters (21 chips for each CBCT scan protocol) were positioned at seven anatomical locations, as illustrated in Fig. 2 and listed in Table 2.

 

Fig. 1. Thermoluminescent dosimeter TLD-100® (LiF) (Thermo Fisher Scientific, USA).

 

Fig. 2. The image of the phantom.

 

Table 2. Anatomical placement of thermoluminescent dosimetry chips within the phantom
Phantom location	TLD ID for each CBCT scan protocol
Throat	Protocol-1:1,2,3, Protocol-2: 22,23,24, Protocol-3: 43,44,45
Teeth	Protocol-1: 4,5,6, Protocol-2: 25, 26,27, Protocol-3:46, 47,48
Cheek	Protocol-1: 7,8,9, Protocol-2:28,29,30, Protocol-3:49,50,51
Eyes	Protocol-1: 10,11,12, Protocol-2:31,32,33, Protocol-3:52,53,54
Frontal (forehead)	Protocol-1: 13,14,15, Protocol-2:34,35,36, Protocol-3:55,56,57
Mid skull	Protocol-1:16,17,18, Protocol-2:37,38,39, Protocol-3:58,59,60
Occipital (back skull)	Protocol-1:19,20,21, Protocol-2:40,41,42, Protocol-3:61,62,63

 

Prior to radiation exposure, the lithium fluoride dosimeters (TLD-100) were calibrated according to the procedures described in the Handbook of Thermoluminescence [22]. The calibration established the relationship between the TLD data and X-ray doses, which was then applied to assess absorbed doses in the phantom’s anatomical regions. For each radiation exposure, 21 dosimeters were used. An additional three TLDs were employed to estimate background radiation, which was measured at 0.013 mGy. The lowest TLD reading recorded was three times higher than this background value, which was subtracted from the TLD readings.

Pre-irradiation annealing of all TLDs was performed in a Muffle furnace- Gallenkamp oven at 400°C for 1 h, followed by low-temperature thermal processing at 100°C for 2 h. Post-irradiation annealing was carried out for 10 min at 100°C [23]. The thermoluminescent reader was a Harshaw model 2000 B/C, manufactured by the Harshaw Filtrol Partnership.

The effective dose (E) was calculated in Sievert (Sv), based on the ICRP60 guidelines, using the following equation [24]:

$E=\sum _T{W}_T\times H_T$, (1)

where W_T is the tissue weighting factor for each tissue (T) or organ, and H_T is the equivalent dose in tissue or in organ.

$H_T=D\times W_R$, (2)

where H_T is the equivalent dose in tissue or in organ, W_R is the radiation weighting factor and D is the absorbed dose.

The value of W_R is one for X-rays [25]. Therefore, the effective dose depends on the absorbed dose (D) and the tissue weighting factors (W_T).

Information on measurement error include factors influencing fading, which involve the type of TLD material (TLD-100 (LiF) dosimeters), dose level (higher doses more susceptible to fading), storage time (longer storage increases fading), and temperature (higher temperatures accelerate fading).

The effects of fading on dosimetry include dose underestimation (fading reduces the measured dose), inaccurate dose assessments (affecting radiation safety and regulatory compliance), and calibration issues (as fading impacts instrument calibration).

Ethics Review

The Ethics Committee of the Department of Basic Sciences, College of Dentistry, University of Basrah, approved this study (protocol No.1022, 07-11-2023).

Statistical Analysis

The statistical package for social sciences (SPSS, version 26, Chicago, US) was used for data analysis. One-way ANOVA followed by post hoc comparison was employed for statistical testing. A 95% confidence interval for the mean and a p-value ≤0.05 were considered statistically significant.

RESULTS

The measured absorbed doses (D) and effective doses (E) for various tissues, including the throat, teeth, cheek, eyes, frontal (forehead), mid-skull, and occipital (back skull) across CBCT scan protocol¹ (low resolution), protocol² (standard resolution), and protocol³ (high resolution) are summarized in Table 3. In the throat, the highest dose was absorbed by tissue² (7.719 mGy). In the teeth, the highest dose was absorbed by tissue3 (16.326 mGy). In the cheek, the highest dose was absorbed by tissue³ (25.053 mGy). In the eyes, the highest dose was absorbed by tissue³ (12.962 mGy). In the forehead, the highest dose was absorbed by tissue³ (8.465 mGy). In the mid-skull, the highest dose was absorbed by tissue³ (20.904 mGy). In the occipital region, the highest dose was absorbed by tissue2 (7.8 mGy). Regarding effective doses, protocol³ resulted in higher values, except in the throat and occipital regions, where protocol² showed greater doses. The observed variations are illustrated in Fig. 3 and Fig. 4, respectively. The indications of statistical significant and non-significant differences between the different protocols and tissues are listed in Table 4.

 

Table 3. Absorbed (D) dose and effective (E) dose across various tissues for each cone-beam computed tomography scan protocol
Protocol-1		Protocol-2		Protocol-3
D (mGy)	E (mSv)	D (mGy)	E (mSv)	D (mGy)	E (mSv)
Throat
0.473 (0.113–1.838)	0.023 (0.011–0.551)	7.719 (1.855–10.551)	0.385 (0.025–1.255)	1.565 (0.951–3.146)	0.078 (0.012–0.544)
Teeth
4.95 (1.453–5.755)	0.049 (0.182-1.222)	13.215 (3.211-25.122)	0.132 (0.911-2.202)	16.326 (2.541-28.512)	0.163 (0.055–1.308)
Cheek
5.378 (0.341–4.662)	0.053 (0.189–2.520)	12.684 (1.024–20.441)	0.126 (0.23–1.599)	25.053 (5.226–30.905)	0.250 (0.155–1.345)
Eyes
2.099 (1.565–7.611)	0.020 (0.997–3.105)	7.577 (0.025–11.259)	0.075 (0.051–1.658)	12.962 (4.467–18.509)	0.129 (0.054–2.411)
Frontal (forehead)
3.46 (2.001–5.133)	0.034 (0.118–1.251)	5.104 (1.052–7.788)	0.051 (0.022–1.422)	8.465 (3.369–10.201)	0.084 (0.055–1.655)
Mid skull
4.894 (0.343–1.526)	0.048 (0.222–0.908)	13.013 (3.522–25.554)	0.130 (1.02–2.487)	20.904 (7.122–36.414)	0.209 (0.190–0.989)
Occipital (back skull)
2.61 (0.902–2.881)	0.026 (1.052–1.558)	7.8 (1.288–9.333)	0.078 (0.011–0.844)	4.188 (0.988–4.322)	0.041 (0.012–0.068)
Note. D — the absorbed dose; E — the effective dose. Results are presented with a 95% confidence interval.

 

Fig. 3. Absorbed (D) dose distribution across various based on different cone-beam computed tomography protocols.

 

Fig. 4. Effective (E) dose distribution across tissues based according to cone-beam computed tomography scan protocols.

 

Table 4. Post hoc comparison indicating significant and non-significant differences between cone-beam computed tomography protocols and tissue doses
Protocols	p-value
	D (mGy)	E (mSv)
1&2	0.0004	0.056
2&3	0.234	0.953
1&3	0.013	0.006

 

DISCUSSION

The highest effective dose was observed with the highest resolution, due to the direct proportionality between resolution settings and effective dose. The results of this study align with earlier research indicating that voxel size settings have an inverse relationship with effective dose [21]. Consequently, it is widely acknowledged that changes in CBCT exposure parameters directly influence the effective dose.

In the CBCT scan protocols, the cheek and teeth received the highest absorbed doses, as these tissues were directly exposed to the primary beam, as shown in Fig. 3. In contrast, the throat and frontal (forehead) regions received the lowest absorbed doses, as these areas were located further from the X-ray beam. The X-rays scattered inside the human body are primarily to blame the irradiation of tissues outside the X-ray beam. The findings of this study concur with those of earlier research that determined the highest and lowest absorbed doses in these tissues [18]. Fig. 4 shows the effective (E) dosages for various tissues, depending on each CBCT methodology.

This study compared the low-, standard-, and high resolution radiation settings on effective radiation doses. As expected, the effective dose was inversely related to voxel size and directly proportional to the resolution, primarily due to the longer exposure times required for higher resolution imaging. This finding is consistent with several published studies [21, 26, 27], which highlight the necessity for high resolution images against the increased radiation hazard associated with these images. Several studies have proposed recommendations to optimize voxel settings and reduce image noise [28]. Therefore, achieving a balance between radiation dose and image resolution is crucial.

The clinical relevance of the dose variations associated with changes in CBCT exposure parameters was evident, as these parameters significantly affected the effective dose. Key factors influencing radiation dose include scanner settings such as tube voltage (higher kVp increasing the dose), tube current (higher mA increases dose), exposure time (longer durations increase dose), and field of view (a larger FOV results in higher doses). Effective dose-reduction strategies should involve selecting appropriate scan protocols, such as low-dose settings for routine examinations.

The key observations from this study include: increasing voxel size reduces resolution but lowers radiation dose, maintaining a constant tube voltage (90 kV) ensures consistent image quality, and protocol 3’s higher tube current improves resolution.

Research Limitations

The primary limitations included a short study period, a small sample size, limited government support, its single-center design, and constraints related to available equipment and facilities.

CONCLUSION

This study demonstrated that variations in CBCT exposure parameters significantly influence the effective dose. Adjustments in resolution selection lead to measurable variations in effective doses, emphasizing the significance of carefully selecting exposure factors such as voxel size and resolution. Dentists must be mindful of their chosen imaging parameters, as they directly impact patient safety.

ADDITIONAL INFORMATION

Author contributions: A. Al-Salihi: conceptualization, data curation, investigation, methodology, project administration, resources, software, writing—original draft, writing—review & editing; A.I.L. Al-Saedi: conceptualization, data curation, investigation, methodology, project administration, writing—original draft, writing—review & editing; S.J. Bader, R.Ch. Abul-Hail: conceptualization, data curation, investigation, methodology, project administration, resources, writing—original draft, writing—review & editing. All the authors approved the version of the manuscript to be published and agreed to be accountable for all aspects of the work, ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Ethics approval: The Ethics Committee of the Department of Basic Sciences, College of Dentistry, University of Basrah, approved this study (protocol No. 1022, 07-11-2023).

Funding sources: No funding.

Disclosure of interests: The authors have no relationships, activities or interests for the last three years related with for-profit or not-for-profit third parties whose interests may be affected by the content of the article.

Statement of originality: When creating this work, the authors did not use previously published information (text, illustrations, data).

Data availability statement: The editorial policy on data sharing does not apply to this work.

Generative AI: Generative AI technologies were not used for this article creation.

Provenance and peer-review: This article was submitted to the journal on an unsolicited basis and reviewed according to the usual procedure. Оne external peer-reviewer and one member of the editorial board were involved in the review process.

About the authors

Abdalrahman Al-Salihi

University of Basrah

Author for correspondence.
Email: abdalrahman.hassan@uobasrah.edu.iq
ORCID iD: 0000-0001-9828-4870

Assistant Professor

Iraq, Basrah

Aqeel Ibrahim L. Al-Saedi

University of Basrah

Email: aqeel.lazim@uobasrah.edu.iq
ORCID iD: 0000-0003-3495-784X

Assistant Professor

Iraq, Basrah

Sattar J. Bader

University of Basrah

Email: sattar.jabbar@uobasrah.edu.iq
ORCID iD: 0009-0009-5841-7929
Iraq, Basrah

Riyadh Ch. Abul-Hail

University of Basrah

Email: riydh.abalhiel@uobasrah.edu.iq
ORCID iD: 0000-0002-1897-3658

Professor

Iraq, Basrah

References

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