A Growing Problem
Today’s practitioners rely on a dizzying array of imaging modalities for both diagnostic and treatment purposes, several of which – including projection radiography, computed tomography (CT), fluoroscopy and positron emission tomography (PET) scans – use ionising radiation to generate images. As a result, medical procedures have become by far the main artificial source of radiation exposure to the general population.
Such exposure can trigger both stochastic and non-stochastic, or deterministic, effects. Stochastic effects are more likely to result from increased exposure, but are not necessarily more severe as a result of higher exposure. These include a higher risk of cancer. While the doses emitted in diagnostic and interventional radiology may increase that risk, sound estimates of radiationinduced cancers remain elusive. By contrast, non-stochastic or deterministic effects, which generally result from short-term exposures to high radiation levels, do become more severe with increased exposure, and often appear quickly. Examples include burns and radiation poisoning.
Technological advances have both alleviated and exacerbated these risks. While innovative devices now include features that facilitate intelligent dose customising, for example, technological progress has also resulted in the introduction of new medical procedures that rely on the use of ionising radiation. In addition, sophisticated health services are increasingly widely and readily available across the globe, meaning that both cumulative radiation doses are increasing, and that more patients, practitioners and medical staff are at risk of suffering negative side effects.
The growing use of CT is particularly striking. The modality entails notably high radiation doses compared to traditional radiography, accounting for only a fraction of total exams performed (under 15%), but for a large percentage (around 65-70%) of imaging radiation (Voress 2007). Nonetheless, thanks to its ability to provide cross-sectional views of organs, it is an immensely popular tool, and its use has multiplied significantly since the early 1990s. In English hospitals, for example, the number of CT scans performed per year rose from around 1 million in 1997 to almost 5 million in 2013 (Elliott 2014). In germany the number increased by 130% between 1996 and 2010, with around 4.88 million patients receiving at least one CT scan in 2009 (Federal Office for Radiation Protection 2014). The trend is even more dramatic in the United States, where the threat of litigation may be pushing practitioners to err on the side of ordering more exams: fewer than 19 million CT scans were performed there in 1993, while 85 million were carried out in 2012 (IMV 2012).
Fluoroscopy is another modality that has triggered considerable debate on balancing risks and benefits. Its ability to provide real-time imaging of internal organs has revolutionised medical treatment, particularly by making possible a variety of interventional radiological (IR) procedures that permit patients to forgo invasive surgery. But its use is also associated with significant radiation doses. Complex IR procedures that involve long exposure times are of particular concern, with embolisation (especially in the brain), the creation of transjugular intrahepatic portosystemic shunts (TIPS), and percutaneous transluminal coronary angioplasty often singled out for entailing high doses. Dose reduction is especially vital for practitioners and other staff members who are chronically exposed. Interventional radiologists, for example, have been found to face an elevated risk of developing radiation-induced cataracts.
Concerns about exposure have already spurred some improvements. Publicity about the increase in CT use did impel manufacturers to lower the dose emitted per scan, resulting in significant reductions. But with reliance on imaging for both diagnostic and therapeutic purposes continuing to expand, heightened awareness is crucial. A recent flurry of initiatives, both at the regulatory and professional society levels, is aiming to achieve that result.
Directing Change through Regulation
The European Union has long immersed itself in radiation protection, both by way of regulatory efforts and by issuing non-binding guidelines. Its latest measure on the issue is Council Directive 2013/59/Euratom of 5 December 2013, laying down basic safety standards for protection against the dangers arising from exposure to ionising radiation. Also referred to as the Basic Safety Standards Directive, it came into force in February 2014. It consolidates and updates a group of previously applicable rules, and member states have until February of 2018 to comply with its requirements.
The Directive reiterates the EU’s commitment to two main principles often invoked in radiation protection efforts in the medical context: the “justification principle”, which requires that decisions that introduce changes in radiation exposure result in more good than harm, viewed either from an individual or a societal perspective; and the “optimisation principle”, which mandates that exposures are to be kept as low as reasonably achievable. Also referred to as the ALARA principle, this concept acknowledges that worse can actually be better, with practitioners encouraged to aim for images that are adequate for diagnosis or intervention, and not necessarily for maximum precision, which generally entails higher exposure levels.
The instrument is comprehensive in scope. Emphasising communication with patients, it obligates physicians to inform patients about the benefits and risks associated with examinations before these take place, and requires resulting reports to include information on patient exposure. Recording and communicating dose information is also a central element of the sections targeting medical equipment. Amongst other things, these require equipment used for IR procedures to provide information about the radiation quantity produced during the procedure. In addition select equipment, including CT, must be able to produce parameter information, based on which practitioners can assess patient dose at the end of a procedure, and transfer this information to examination records. (Equipment installed before the Directive enters into force may be exempt from parts of these requirements.)