Contemporary issues in radiation protection in medical imaging: introductory editorial

Radiation protection has always been a central aspect to medical imaging, but its importance has varied in emphasis over the years. For almost a century after the discovery of X-rays in 1895 and radioactivity in 1896, the major attention was on occupational radiation protection. Patient radiation protection gained prominence much later and remains an essential priority today.1,2 A number of international organisations such as the International Commission on Radiological Protection (ICRP), International Atomic Energy Agency (IAEA), European Commission, World Health Organisation (WHO) and several regional and national organisations have contributed immensely to development of policies and standards that have then found their way into national regulatory requirements and guidelines.3 While the regulatory mechanisms have been ingrained into occupational radiation protection, advisory mechanisms have remained dominant for patient radiation protection with the exception of mammography. There have been times when the need for regulatory control on patient doses has been raised,4–6 but the policies have largely remained unchanged with apprehension that regulatory control on patient doses may hamper the benefits which have been thought to outweigh the risks. We are now at the crossroad where the potential risks have reached a level where strategic planning seems urgent.7,8 This need has been highlighted with a series of publications on high cumulative doses from medical imaging in the past 3 years that create a compelling situation to be addressed.8–15 It is very timely that this special feature in BJR has collected a series of articles that deal with contemporary issues at hand that are likely to shape the direction of patient radiation protection. The special feature has five thought-provoking papers on recurrent imaging. Brower and Rehani8 review a compilation of studies in both radiology and nuclear medicine, including hybrid imaging, that result in high cumulative effective dose (CED) to patients. They point out that we have entered an unprecedented era in imaging practices wherein 1 out of 125 patients undergoing CT imaging can likely be exposed to effective dose >50 mSv from a single CT exam and 3 out of 10,000 patients could potentially receive CEDs > 100 mSv in a single day.16 Presently, we do not know the cumulative doses that patients may be receiving across all imaging modalities combined. While justification and optimisation remain paramount, they emphasise that the current situation requires imaging device manufacturers to urgently develop technologies that are safer for patients by acquiring diagnostic quality images at the lowest dose achievable. Further, there is a need to have a critical look at the fundamental principles of radiation protection as cumulative doses are likely to increase in the coming years. While discussing the stochastic radiation risks, they assert that the future must include debate on the controversy of incorporating cumulative dose into clinical decision-making. The IAEA’s Vassileva and Holmberg17 complement the above paper by reviewing recurrent imaging and confirming the need for patient-centric healthcare in an era where cumulative doses are likely to increase. The radiation protection framework will need to respond to the challenge of recurrent imaging and high individual doses. The radiation protection perspective is a counterpart to the clinical perspective, and the risk–benefit analysis must account holistically for all incidental and long-term benefits and risks for patients, their clinical history, and specific needs. They point to the literature on specific clinical indications which can result in a higher imaging frequency while also collating population-based studies of large cohorts. High individual doses for recurrent imaging instances drives the need for integration of clinical and exposure history. The central message of these two papers is that we have reached a stage where we were never before and that pertains to millions of patients receiving organ doses where radiation effects are very likely to occur as per our current knowledge. There have been indications in the past that cumulative doses can be high, but the scale to which recent research has demonstrated the magnitude was unexpected. Technological developments allowing the tracking of individual patient doses has enabled this insight. It is almost a decade since momentum on tracking of imaging exams and doses started to pick up.18–21 The new observations and reviews in papers in this journal shall guide the directions and hopefully help actions of ICRP, IAEA, EC, WHO and many other organisations in framing policies and guidelines. Brambilla et al.22 did a systematic review of the published papers on the cumulative doses in nuclear medicine examinations in selected cohorts of adults or paediatric patients. They point out the need for prospective, multicentric studies enrolling a greater number of patients, followed for longer periods in selected groups of patients to fully capture the cumulative exposure to radiation. Their review identifies selected groups of patients with a specific health status in which the cumulated exposure to radiation may be of concern, and where the contribution of nuclear medicine procedures to the total CED is significant. Hosono et al.23 draw attention to a paucity of publications on the frequency of patients with a CED ≥ 100 mSv from PET–CT examinations and emphasise the implementation of justification for PET–CT examinations and utilisation of dose reduction measures for coping with the high cumulative dose in patients. With recent emphasis on cumulative dose, the most crucial question that haunts us all is can imaging history be incorporated into decisions about when to image again? Sodickson24 presents a framework to consider these issues in a potentially at-risk population, the so called “frequent flyers”. He points out that the complexity and variability of the underlying disease states and trajectories argue against alerting mechanisms based on a simple cumulative dose threshold. Awareness of imaging history may instead be beneficial in encouraging physicians and patients to take the long view, and to identify those populations of frequent flyers that might benefit from alternative imaging strategies. A remaining difficulty is determining the appropriate “dose quantity” to use while accounting for radiation exposure of a patient with multiple imaging episodes of different body parts, some using X-ray while others using radiopharmaceuticals. Frush acknowledges the challenges with the use of effective dose, but decides it is still the most prevalent currency for recurrent imaging examinations.25 He points out differences between the paediatric and adult population, including the fact that high cumulative doses (e.g. >100 mSv) are reported to occur much less frequently in children than in the adult population. He suggests review of the general construct of CED to incorporate various features of paediatric patients. There is of course a need for patient-specific dose.26 Miller et al.27 provide elaborate information on the U.S. Food and Drug Administration’s (FDA) role in improving radiation dose management for medical X-ray imaging devices that are regulated under both FDA’s electronic product regulations and FDA’s medical device regulations. FDA encourages manufacturers to develop medical devices that conform to voluntary consensus standards. Use of these standards is a central element of FDA’s system to ensure that all medical devices marketed in the U.S. meet safety and effectiveness requirements. Use of voluntary consensus standards reduces the amount of time necessary to evaluate a premarket submission and reduces the burden on manufacturers. FDA works with all stakeholders to achieve its mission of protecting and promoting public health. Realising that science behind radiation effects plays an important role in decision-making in the day-to-day practice of radiology and nuclear imaging, an article by Berrington de Gonzalez et al. reviews the state of science in epidemiological studies of CT scans and cancer risk.28 They provide a comprehensive assessment that draws together 17 eligible studies in this field. This review is timely as publications of these types of studies are relatively slow to appear, possibly due to the challenges of pooling data to provide improved risk quantification, individual dosimetry and the difficulty in accounting for confounding by pre-existing conditions and the role of reverse causation. It is however clear that the cohort of millions of patients identified in several of these studies7,8,10,29,30 can prove a valuable resource for future studies on radiation effects,2,31 and this needs to be tapped by researchers, while funding organisations need to include this research in their prioritisation.31 There has been increasing use of fluoroscopic-guided intervention (FGI) in various clinical specialties and the applications continue to grow.32,33 Clinicians performing these FGI procedures have typically lacked appropriate training in many countries but they make use of radiation to a level where radiation-induced skin injuries have been reported over the past nearly three decades and continue to occur.34–36 It may be pleasing for readers to note the article by a gastroenterologist on radiation doses involved in endoscopic procedures in gastrointestinal and hepatobiliary disorders. Takenaka et al.37 provide radiation doses in diagnostic and therapeutic ERCP (endoscopic retrograde cholangiopancreatography procedures) and draw attention to over couch-type X-ray units where the eye dose to the operator per procedure reached as high as 550 μGy, with maximal doses of up to 2.8 mGy/procedure. Even though this BJR special feature is focused largely on patient radiation protection, the active topic of cataract risk due to occupational exposure has also been covered.38,39 A review by Schueler and Fetterly40 points to significant variability in reported doses to the lens of the eye and indicates high dependence on individual actions for the possibility of reduction in exposure. They also indicate further follow-up studies of staff lens opacification and correlation with eye lens dose measurements under current clinical practice conditions. There has been debate in recent years regarding whether shielding of radiosensitive organs of patients in imaging procedures is necessary, and it has drawn the attention of several organisations in the past couple of years.41,42 In a Commentary in this issue, Hiles43 points to a growing body of evidence that the practice of placing radiation protective shielding on patients ("in contact") in order to reduce the dose to certain radiosensitive organs for diagnostic X-ray examination that has been employed for decades may be ineffective or even counterproductive and the use of such shielding can also overemphasise the hazards of ionising radiation in the public mind. To improve the transparency of these recommendations, it is therefore suggested that a threshold for dose and/or risk should be clearly stated, below which no protection is required. A suggested starting point for defining this threshold is discussed. Artificial intelligence appears to be the future of medical imaging with the impact it has created among manufacturers of imaging equipment, researchers, and radiologists. Seah et al.44 while providing an overview of the commonly used deep learning techniques as applied to tomographic reconstruction, guides actions to reduce patient radiation dose. The paper also reviews some of the estimated dose reductions in CT and PET imaging in the recent literature enabled by deep learning, some of the potential problems that may be encountered such as the obscuration of pathology and highlights the need for additional clinical reader studies from the imaging community. Image quality aspects have been covered in many of the papers in this special feature, however, readers are referred to recent papers for further details.45–47 Any dose management action, whether at the level of user or manufacturer, needs to maintain the desired image quality to achieve the clinical purpose and this is typically indicated in most papers on dose management. There is urgent need for scientists involved in the study of radiation effects to provide guidance on availability or non-availability of evidence of radiation effects when imaging radiation doses are accumulated by patients over time.31 This should cover differences in radiosensitivity with age and gender. Despite evidence lacking in reported literature of potential misuse of cumulative doses to refuse a needed examination, there remains fear of misuse of cumulative dose. Future steps must be evidence-based, rather than driven by repercussion. Training needs to be strengthened to include a better understanding of contemporary and new issues pertaining to cumulative dose to avoid misuse and misunderstanding. We hope that this BJR special feature shall provide useful material on issues that confront all of us in the field of patient and staff radiation protection. The invited articles cover the latest research in the clinical arena in the field of medical imaging and compile the most current research on many topical areas. We, Madan and Zoe, wish to thank all contributors to this collection. We also wish to thank the experts who reviewed the papers without whom we could not have produced this exciting special feature in BJR. We are hopeful that readers will relish the papers, find them exciting and put the findings to use in their day-to-day work.