Diagnostic reference levels in low- and middle-income countries: early “ALARAm” bells?

Introduction

Medical imaging is recognized by the World Health Organization (WHO) as an essential component of any healthcare system (1). Substantial technological developments in diagnostic imaging in recent decades have contributed to increasing clinical use of radiological services worldwide. Between 1988 and 2008, the number of diagnostic imaging studies increased 128%, from approximately 1.38 billion to 3.14 billion per annum globally. In the same period, the number of radiological examinations performed per 1000 of the world’s population increased from 280 to 488 annually (74%) (2). This growth in the world’s utilization of diagnostic imaging is reflected in the global per capita effective medical radiation dose, which increased from 0.40 mSv to 0.62 mSv (55%) between the periods of 1991–1996 and 1997–2007 (2).

Major national and multinational surveys of medical radiation exposure were first conducted in the 1950s with surveys such as the Adrian Survey in the UK as well as the United Nations UNSCEAR survey (3,4). Subsequent landmark surveys in the USA in 1973 and UK in 1986 highlighted significant inter-facility variability in mean radiation dosages for the same investigation (5,6) and culminated in the publication of procedure-related national radiation-dose guidelines for the USA and UK in 1985 and 1990, respectively (3). In response to the global increase in medical radiation exposure, the variations in procedure-specific radiation dosages, and the known risks of ionizing radiation, the International Commission on Radiological Protection (ICRP) introduced the concept of diagnostic reference levels (DRLs) in 1996 (7).

National DRLs can be established for specific examinations and patient groups, based on dose distributions recorded in national surveys. The third quartile, being the level below which 75% of all recorded data fall, is the radiation dose most commonly adopted as the reference level (8). Similarly, authorized bodies can determine regional DRLs for a specific geographical area.

Local DRLs (LDRLs) can also be determined for a hospital or an imaging practice, representing the mean dosage for a specific examination at a single institution (9). DRLs are intended to play a leading role in radiation protection, by providing an easily measured quality assurance quantity for radiation dose optimization (10). Ideally, DRLs monitor procedure-specific radiation dosage, define optimal dose parameters, identify high-radiation “outliers,” facilitate comparisons of equipment and protocols, and provide a mechanism for fine-tuning patient absorbed dosages (8,11).

Since the introduction of DRLs in 1996, the concept has been widely embraced. Both the International Atomic Energy Agency (IAEA) and the European Union (EU) require that member states promote their establishment and use (12,13). There are also well documented DRLs for the UK (14,15), USA (16), Canada (17), Japan (18), Australia (19), and the Russian Federation (20). However, available DRL data are largely from countries (n = 80) classified as “high-income” by World Bank criteria (21). There is a relative paucity of data from the 135 countries classified by the World Bank as “low- or middle-income” (LMIC), where more than 80% (n = 5.85 billion) of the world’s 7.26 billion population reside. There is arguably a greater need for DRLs in LMICs, where lower per capita healthcare budgets may translate into older imaging equipment and fewer trained imaging technicians (21).

To date, there has been no critical analysis of the published work on DRLs in LMICs. Such a review is important since it will serve as a broad measure of quality assurance in the field of diagnostic imaging in resource-constrained healthcare infrastructures, and could inform, stimulate, and direct future initiatives in this domain. The purpose of this study was therefore to review the published work on DRLs in LMICs and to critically analyze the comprehensiveness of available data.

Material and Methods

Medline, Scopus, and Web of Science searches were conducted using the key words “radiation” and “dose” and “reference” and “level” or “DRL” or “LDRL”. All English-language articles published between 1996 and 2015 which documented dose reference levels for diagnostic imaging procedures conducted in LMICs, as defined by World Bank criteria (21), were included. The titles and abstracts of potential articles were reviewed and the full manuscripts of eligible publications retrieved. The reference lists of eligible publications were assessed for possible additional data. Articles were analyzed and classified by World Bank income level, World Bank geographical region, country of origin, contributing author, sponsor, year of publication, imaging modality, local/regional/national DRL, body part, and patient age. Where a single publication documented DRLs for more than one country, all countries were appropriately credited.

Descriptive statistics were formulated. The proportion of LMICs with DRLs in respective imaging modalities defined the comprehensiveness of available data.

Results

Discussion

To the best of our knowledge, this is the first comprehensive review of the published work on DRLs from LMICs. As such, it makes an important contribution to the body of knowledge on quality assurance and radiation protection in diagnostic imaging. Furthermore, the analysis is timely; two decades have now passed since the ICRP first introduced the notion of the DRL.

This work highlights the need for up-scaling of DRL initiatives in the large majority of LMICs. This is especially true for low-income-countries, since 94% have no such published data. The accurate recording and reporting of DRLs is increasingly being recognized as a basic safety requirement in medical imaging. This is underscored by the recently promulgated European Directive stipulating that the use and regular review of DRLs will be a statutory requirement for all EU Member States from February 2018 (22).

While there are substantial discrepancies between high-income countries and LMICs with respect to diagnostic imaging resources (23–25), it is salutary to note that the need for DRLs is independent of the quantum of a country’s imaging equipment per se. Nonetheless, multiple related factors may contribute to the paucity of published LMIC DRL data, including the dearth of regulatory authorities governing the use of medical imaging equipment, as well as the potential failure on the part of existing bodies to implement appropriate quality assurance procedures (1,26).

Human resource limitations are an additional challenge, particularly with respect to highly qualified personnel such as medical physicists and radiologists. The number of medical physicists in LMICs is well below the level required to provide even the most basic professional support in diagnostic imaging and radiation therapy (26). In 2010, it was estimated that there were approximately 18500 qualified medical physicists worldwide, with 15–20 per million population in well-resourced countries and between 0–5 per million population in LMICs, with many low-income countries having no medical physicist (27). Moreover, high-income countries have between 47 and 110 radiologists per million population (28,29), while some low-income countries in sub-Saharan Africa have no public sector radiologist (30,31). The LMIC challenge is to build capacity, acquire appropriate equipment, and to both train and retain the necessary highly specialized personnel within very stringent budgetary constraints (26).

The striking lack of published DRL data from low-income countries suggests that there may be a critical mass of key resources that are required to generate such data. In this context, the notion of the “radiology enterprise” is useful (32), being a loose organization of imaging modalities, specialized staff, and quality assurance instrumentation dedicated to the delivery of medical imaging services. It could be that below a certain collective resource threshold, a country’s “radiology enterprise” is incapable of generating appropriate DRL data. Future work could be undertaken to define the key components and the minimum resources required for generating basic data in low-income countries.

Despite the relative paucity of existing data, there is an encouraging trend of increasing DRL publications in recent years, with more than half of all manuscripts (n = 29; 54%) having been generated in the last four years. The IAEA has already been instrumental in initiating important DRL outputs in Latin America. The WHO has included the establishment and regular updating of DRLs as part of its “Bonn call for action” to improve radiation protection in medicine (33). Both the IAEA and the World Health Organization, as well as non-government organizations such as the International Organization for Medical Physics, European Federation of Organizations for Medical Physics and the International Radiation Protection Organization could potentially prioritize further LMIC projects and lobby governments to exercise stronger regulatory control in this domain.

A further encouraging trend is the involvement of radiographers in DRL publications from South Africa and Nigeria. Radiographers could be empowered to assume greater responsibility in this domain as part of a strategic “task shifting” policy. Task shifting is a method of expanding the health workforce by delegating work from more- to less-specialized healthcare workers who can competently perform the task. There is growing realization that some form of task shifting will be required at many levels of healthcare in the future, to facilitate more equitable access to services (34,35).

This study was limited by being confined to English-language articles, with the attendant potential for under-reporting, given the language diversity within LMICs. Notwithstanding this, the published English language data presented in this analysis are from a broad spectrum of LMICs, many of which do not have English as the national language. It is thus considered unlikely that such bias could materially influence the conclusions of this manuscript.

A further limitation is the potential for unpublished LMIC DRL data. A number of factors may contribute to such data remaining unpublished. Clinical radiologists and medical physicists in resource-limited environments tend to be overburdened by clinical duties, with little time for manuscript preparation. Additionally, attempts at publication of available data may be unsuccessful. Factors implicated in manuscript failure include increasingly stringent journal acceptance criteria, with high rejection rates, and limited appreciation of the uniqueness and importance of DRLs from LMICs. It is hoped that this manuscript will highlight the latter. The authors acknowledge that the absence of published DRL data not does necessarily imply improper dose control, since dose optimization may be based on published DRLs from other countries or bodies, including the European Commission. The dearth of published data more likely reflects the limited imaging infrastructure in resource-constrained environments.

In conclusion, diagnostic reference levels are important parameters in the process of radiation dose optimization and thus an important component of quality assurance in diagnostic radiology. It is hoped that this analysis will serve as a stimulus for up-scaling of DRL initiatives in LMICs.