PHWR Public Health Weekly Report

Radiography is essential for precise diagnosis and treatment. However, given the inherent risk of radiation exposure, medical radiography should be conducted with utmost care to minimize radiation levels while preserving patient benefits. To address this, global initiatives have centered on analyzing and implementing the national diagnostic reference level (DRL). DRL represents the third and fourth-quartile values derived from a comprehensive national survey of radiation levels utilized in hospitals for specific examinations. The dose-area-product (DAP; unit: mGy∙cm2) serves as the dose metric.

The primary objective of DRL is to empower healthcare providers to optimize radiography procedures and consequently reduce overall medical radiation exposure at a national level. By comparing their dose levels to DRL, medical institutions can evaluate the effectiveness of radiation protection measures and image quality. This enables them to refine radiography protocol accordingly.

In the field of dentistry, the utilization of cone-beam computed tomography (CBCT) has proliferated since its introduction in the 1990s. Correspondingly, concerns and interest regarding dental radiation have intensified. According to the Health Insurance Review and Assessment Service (HIRA), CBCT availability has increased by approximately 53% over the past 5 years, with more than half of dental hospitals and clinics currently employing CBCT (Figure 1) [1,2].

Figure 1. The current state of radiographic equipment in the dental field in the Republic of Korea
(A) Number of dental radiology equipment installations (Reused from Health Insurance Review and Assessment Service [1]). (B) Status of introduction of cone-beam computed tomography (CBCT) equipment in the Republic of Korea (Reused from Health Insurance Review and Assessment Service [2]).

Conventional dental radiography, while frequently administered to patients of all ages, involves relatively low radiation doses. Conversely, CBCT utilizes significantly higher radiation levels [3]. Similar to other dental examinations, CBCT scans are utilized regularly for treatment, diagnosis, and surgical planning [4]. Consequently, the widespread adoption of CBCT is considered a primary factor in the increasing exposure to dental radiation. As CBCT use has grown and public awareness of radiation risks has heightened, effective patient education and radiation management have become crucial in dentistry. While many dental providers express concerns about CBCT radiation exposure, precise radiation levels from their equipment are often uncertain. Therefore, optimizing radiography through regular analysis and the establishment of DRLs is essential in dental practice.

Several countries, including the United States, the United Kingdom, Japan, and Republic of Korea (ROK), have implemented DRLs for dental radiography (Table 1) [5,,-8]. ROK initiated a five-year DRL cycle in 2004 to reduce radiation exposure; however, compared to European nations with stricter radiation protection regulations, significant opportunities remain for dose reduction in Korean dental radiography. Establishing DRLs requires considering the geographical distribution of dental clinics, with on-site visits to selected dental hospitals for data collection. In ROK, CBCT DRLs are currently based on maxillary implant procedures [5], while other countries often rely on on-site or questionnaire surveys. To enhance DRL reliability, a broader inclusion of dental clinics and a comprehensive examination of various protocols is necessary, although practical limitations exist.

Table 1 Comparison of national diagnostic reference levels by country

Type of examination		Korea (2019) [5]	United States (2019) [6]	United Kingdom (2019) [7]	Japen (2020) [8]
Panoramic radiography	Adult	227	123	81	134
	Child	163–175	67	60	-
CBCT	Adult	2,060	727	265	1,960
	Child	1,208	624	169	-

Unit: mGyㆍcm². CBCT=cone-beam computed tomography..

The American College of Radiology operates the Dose Index Registry to optimize radiation doses for multi-slice CT examinations. Directly linked to testing equipment or compatible with dose management programs, the registry calculates DRLs for CT, enabling institutions to compare their dose levels to national or regional benchmarks [9]. This overcomes challenges associated with large-scale on-site surveys.

A growing awareness of automated dose collection systems has led to recent instances of monitoring radiation exposure through CBCT equipment linked with commercial dose programs [10]. Notably, ROK’s CBCT equipment now surpasses the number of installed multi-slice CT units [11], necessitating robust national dose management. Implementing an automated system for dose information management would facilitate the accurate collection and management of large-scale dose data. This policy study aims to adapt the existing CT system for dentistry and introduce a national dose management system for dental radiography.

1. Status of Dental Radiation Equipment Installed in the Republic of Korea

A 2023 investigation based on Korean Statistical Information Service data assessed dental equipment status across ROK. Of the 44,985 identified operational equipments, approximately 38% (n=17,519) were CBCT units, while panoramic radiography accounted for approximately 9% (n=4,179). The lower number of panoramic systems reflects the increasing prevalence of combined panoramic and CBCT units, categorized as CBCT equipment. Notably, less than approximately 27% of CBCT units provided dose information in DAP format.

Medical images are standardized in digital image and communications in medicine (DICOM) format, encompassing image data, patient information, equipment details, examination date, institution, and radiation exposure conditions. While the DICOM standard mandates DAP output for all dental radiography equipment, ROK’s adoption of DAP-capable models is relatively recent.

2. Characterization by Radiography Equipment and Examination Site and Code Design

To establish a national dose management system for dental radiography, we analyzed the characteristics of individual radiographic equipment to create a system accommodating diverse equipment types [12]. Unlike panoramic and CBCT units, intraoral radiography often involves independent radiation generators and image receptors. Thus, a system capable of handling such configurations was essential. We focused on developing a comprehensive data accumulation method to capture dose data from individual equipment within each hospital.

To characterize examinations, we aligned the examination prescription information system with HIRA codes. We analyzed the relationship between exposure dose and individual codes within each equipment type. While some order codes differentiated exposure levels (e.g., temporomandibular joint and maxillary sinus panoramic radiography), HIRA codes and doses for intraoral radiography and CBCT were largely unrelated. CBCT, a dose contributor, was primarily differentiated by three-dimensional volume reconstruction codes. Consequently, a new coding system was necessary.

Given the minimal radiation exposure variations among individual teeth and the potential increase in system complexity, intraoral radiography was classified based on imaging technique (periapical and bite-wing) rather than dental formula. For CBCT, a new code system was devised with a primary emphasis on field-of-view and examination sites, as these factors significantly influenced dose. The proposed five-digit code structure encompassed the type of examination (first digit), major (second digit) and subcategory (third digit) of prescription, arbitrary serial number (fourth digit), and age (fifth digit) (Table 2).

Table 2 A coding system for dental radiology doses by examination type and prescription

First		Second		Third		Fourth	Fifth
Type of examination		Prescription name large classification		Prescription name minor classification		Serial number	Age group
I	Intraoral radiography	1	Bitewing	0	-	Random serial	A C	Adult Child
		2	Periapical view
		3	Tube-shift
		4	Occlusal
P	Panoramic radiography	1	General mode	0	-
		2	Special mode
C	CBCT	1	Large (~15×15 cm)	1	Facial, TMJ
				2	Maxilla
		2	Medium (~10×10 cm)	3	Mandible
				4	Panoramic, jaw
		3	Small (~5×5 cm)	5	Implant
				6	Tooth, endo

CBCT=cone-beam computed tomography; TMJ=temporomandibular joint..

3. System Design

According to the DICOM standard, dental radiographs, encompassing intraoral radiography, panoramic radiography, and CBCT image files, must be capable of generating a radiation dose structured report (RDSR) (Figure 2) [13]. While CBCT, a relatively recent technology, initially lacked RDSR output capabilities, the implementation of stricter regulations in 2011 mandated that CBCT equipment manufactured thereafter include dose value (DAP) in the DICOM header.

Figure 2. Analyze cone-beam computed tomography (CBCT) structure documentation in digital image and communications in medicine radiation dose structuring reports (RDSR)
Reused from Digital Imaging and Communication in Medicine [13].

To accommodate these equipment variations, the system design incorporated a dual-path approach. DICOM files were simultaneously transmitted to both the image viewer system and the dose management system agent upon image acquisition. In instances where dual-path output was infeasible the image viewer system (picture archiving and communication system) served as the intermediary for file transmission to the agent (Figure 3). This system architecture was informed by a previously developed dental radiography dose analysis system in the ROK [12].

Figure 3. A schematic of a dose management system design
CBCT=cone-beam computed tomography; PACS=picture archiving and communication system; DAP=dose-area-product.

The dose management system extracted only dose values from the agent, transmitting fully anonymized data to the server. Subsequent analysis of this data enabled the circulation of DRLs for each defined examination code. The system was configured to deliver comparative tables, graphs, and relevant DRLs to individual medical institutions, empowering them to independently optimize dose levels.

Radiation has been a cornerstone of medical treatment for an extended period, with its significance and application steadily expanding. Advanced nations such as the United States, the United Kingdom, and Japan have been proactive in radiation reduction, implementing DRLs based on comprehensive national surveys of high-radiation CT examinations. In ROK, the Korea Disease Control and Prevention Agency has spearheaded multifaceted initiatives to reduce medical radiation, including a radiation dose management system and research on radiological examination appropriateness.

Historically, dental radiography, despite its widespread use across diverse populations, has received less stringent regulatory attention due to relatively low radiation doses. However, the advent of CBCT in the 1990s and its subsequent proliferation have led to a substantial increase in dental radiation exposure, necessitating focused attention. This study aimed to develop a comprehensive radiation dose management system capable of integrating various dental equipment, enabling real-time surveillance of dental hospitals and clinics, and facilitating the regular generation of accurate DRLs.

The proposed system was designed to collect dose data from equipment compliant with DICOM standard. Nevertheless, a substantial portion of dental equipment, varying by manufacturer and model, deviates from DICOM standards, hindering full system implementation. Collaborative efforts involving hospital administrators, manufacturers, and government agencies are essential to address these limitations and promote system upgrades and expansion.

Given the ubiquitous use of radiation equipment, even at the clinic level, prudent management is essential in dentistry. The prevalence of non-digital equipment in many facilities further complicates matters, as dose information is often unavailable at the equipment level. CBCT, in particular, demands stringent management due to its higher radiation exposure than conventional dental radiography. Despite this, the fact that 73% of CBCT equipment does not output dose information is a critical issue. Considering the predominance of domestically manufactured equipment in Korean dental clinics, targeted efforts to align domestic production with international standards and specifications can significantly improve the situation.

A systematic approach to upgrading dental equipment radiation dose management is necessary, including stricter inspections for radiation dose labeling during equipment licensing, installation, and examinations. While progress has been made with the 2011 mandate for radiation dose information on x-ray control panels by the Ministry of Food and Drug Safety, and subsequent DAP output in CBCT DICOM information, challenges persist in managing radiation exposure for intraoral and panoramic radiography. The separate combination of detectors and x-ray tubes in intraoral radiography often precludes DICOM information generation. Although intraoral radiography involves relatively low radiation doses, its widespread use, especially in pediatric and general populations, necessitates careful dose management. Continuous education and promotion of DICOM specifications related to dose information are crucial.

Effective implementation of a national dental radiography dose management system requires input from various stakeholders. Ongoing system upgrades and expansion can be facilitated through collaborative efforts. Additionally, individual facilities can contribute to dose reduction through in-house quality control measures. Government support, including the provision of DRLs, is essential for assisting hospitals in effective dose management. Institutional incentives such as rewards and certification programs can encourage voluntary participation among dental hospitals and clinics, fostering a culture of radiation safety. Ultimately, widespread engagement from dentists, radiologists, and dental hygienists is crucial for enhancing awareness and driving system improvement. Through concerted efforts from all stakeholders and sustained government support, significant progress can be made in reducing dental radiation exposure.

The developed national dose management system comprehensively integrates all dental equipment, including multi-devices, intraoral radiography, panoramic radiography, and CBCT, serving as a foundational platform for establishing dental radiography DRLs. Ongoing system upgrades, promotion, and expansion are anticipated to yield more precise DRLs based on actual patient radiation exposure. DRLs empower users to independently optimize radiation practices while informing national medical radiation management policies. To sustain this system, collaborative efforts among users, manufacturers, and the government are essential to ensure dental medical equipment adherence to medical imaging standards.

Ethics Statement: Not applicable.

Funding Source: This work was supported by the Research Program funded by the Korea Disease Control and Prevention Agency (2023-10-007).

Acknowledgments: None.

Conflict of Interest: The authors have no conflicts of interest to declare.

Author Contributions: Conceptualization: JHW, JWG, YJM. Data curation: JYL, CNL, JSK, SWY. Formal analysis: JYL, JSK. Funding acquisition: YJM. Investigation: JYL, CNL, JSK, SWY. Methodology: JSK, JWG. Project administration: CNL, JSK, SWY. Resources: JSK. Software: JSK. Supervision: CNL, JSK, SWY. Validation: JHW, JWG, YJM. Visualization: JYL, CNL. Writing – original draft: JYL, CNL. Writing – review & editing: JYL, CNL, JSK, SWY, JHW, JWG, YJM.