Radiation exposure during angiographic interventions in interventional radiology – risk and fate of advanced procedures

Abstract

Purpose

Advanced angiographic procedures in interventional radiology are becoming more important and are more frequently used, especially in the treatment of several acute life-threatening diseases like stroke or aortic injury. In recent years, technical advancement has led to a broader spectrum of interventions and complex procedures with longer fluoroscopy times. This involves the risk of higher dose exposures, which, in rare cases, may cause deterministic radiation effects, e.g. erythema in patients undergoing angiographic procedures. Against this background, these procedures recently also became subject to national and international regulations regarding radiation protection. At the same time, individual risk assessment of possible stochastic radiation effects for each patient must be weighed up against the anticipated benefits of the therapy itself. Harmful effects of the administered dose are not limited to the patient but can also affect the radiologist and the medical staff. In particular, the development of cataracts in interventionalists is a rising matter of concern. Furthermore, long-term effects of repeated and prolonged x-ray exposure have long been neglected by radiologists but have come into focus in the past years.

Conclusions

With all this in mind, this review discusses different efforts to reduce radiation exposition levels for patients and medical staff by means of technical, personal as well as organizational measures.

Keywords:

• Interventional radiology
• radiation protection
• fluoroscopy
• dose reduction

Introduction

In recent years, angiographic procedures in interventional radiology (IR) have been used more widely and embrace new and often advanced therapy options for several diseases. In the treatment of acute ischemic stroke and ruptured cerebral aneurysms, for example, interventional procedures represent valuable and often superior therapeutic approaches compared to surgical treatment (Fransen et al. 2014; Ellis et al. 2018). Furthermore, in the care of trauma patients, e.g. suffering from spleen laceration or aortic dissection, interventional procedures are meanwhile recommended as standard in many cases (Gould and Vedantham 2006). It is therefore not surprising that numbers of performed interventions have continuously risen during recent years in Germany, the US and other countries, respectively (Tsapaki et al. 2009; Schegerer et al. 2019; Mettler et al. 2020). More complex interventions often result in higher dose burdens for patients (Miller et al. 2003) and especially fluoroscopically guided interventions affect patients (Vano et al. 2008) as well as attending medical staff alike (Chida et al. 2013). The administered doses applied in angiographic procedures range from very low doses (e.g. peripheral artery occlusion therapy) to high doses for special treatments (e.g. endovascular aortic repair (EVAR)) and may even reach exorbitant levels under special circumstances (Jaschke et al. 2020). Hence, deterministic effects, such as cutaneous radiation injuries and cataracts have been repeatedly reported (Balter et al. 2010; Rehani and Srimahachota 2011; Vano et al. 2013; Balter and Miller 2014).

As a consequence, interventionalists are obliged to conduct a profound benefit–risk assessment prior to each intervention next to paying careful attention to the ALARA-principle and general radiation safety measures. At the same time, radiation exposure among medical professionals has to be considered in interventional procedures as well. Having this in mind, great efforts have been made in recent years to advance radiation protection and reduce administered doses in interventional procedures – not only in terms of technical improvements but also organizational measures and tightened regulations (Bartal et al. 2014; Meisinger et al. 2016; Koenig et al. 2019; Loose et al. 2020; Tsapaki 2020).

In this review, we emphasize possible effects of radiation exposure to patients and medical staff, describe typical exposure levels of different interventional procedures as well as discuss different technical and practical approaches to reduce radiation exposure in IR.

Interventional fluoroscopy as high-dose procedure

The terms ‘high-dose’ and ‘low-dose’ are commonly used in the context of radiation application ranging from radiation protection to environmental exposure or from radiotherapy to simple X-ray diagnostics. However, these terms are occasionally associated to different dose values causing a misunderstanding when talking about ‘high-’ or ‘low-dose’ radiation exposure (Sohrabi 1997). Within the field of radiology, angiographic interventions and computed tomography are usually referred to as high-dose procedures (Hall and Brenner 2008; Mettler et al. 2008; Jaschke et al. 2020). At the same time, applied dose levels in IR vary depending on the region of interest as well as complexity of the intervention with commonly higher doses in abdominal and neurointerventional procedures among others (Miller et al. 2003; Lee et al. 2019). As an example, dose ranges for angiographic interventions in national reference levels for Germany differ up to factor 10 (from 2500 cGy*cm² dose area product (DAP) in lower leg percutaneous transluminal angiography to 25,000 cGy*cm² DAP in intracranial cerebral aneurysm repair) (Loose et al. 2020).

Radiation effects

Since earliest reports on adverse effects caused by X-ray radiation in humans (Frieben 1902), awareness on radiation protection has risen dramatically. Despite technological progress and decreasing dose exposure in general, the complexity of modern interventional procedures may still entail deterministic effects in rare cases. In particular, cutaneous radiation damage following angiographic interventions with peak skin doses exceeding 2 Gy has been described in this context repeatedly (Balter and Miller 2014). The relevance of this adverse effect is underlined by a recent revision of German law on radiation protection in line with European regulations (EU Directive 2013/59 EURATOM). In concrete terms, a dose excess >50,000 cGy*cm² DAP during an interventional procedure with resulting deterministic skin damage of second or higher degree within 21 days after exposure has to be reported by the attending physician (Walz et al. 2019).

In addition, increasing evidence of X-ray-induced cataracts within interventionalists as a further entity of deterministic effect has alarmed the medical society in recent years (Jacob et al. 2010; Vano et al. 2010; Koukorava et al. 2011; Jacob et al. 2013; Vano et al. 2013; Vano et al. 2015; Kato et al. 2019). The primarily assumed threshold dose for induction of lens opacities of more than 2 Gy (Bartal et al. 2014; Dauer et al. 2017) is challenged by statistical analysis of data originating from atomic bomb survivors. According to this, no definite threshold dose for lens injuries and beginning manifestation of cataracts slightly below 100 mSv lens dose appear plausible (Nakashima et al. 2006; Neriishi et al. 2007). As a consequence, new recommendations of the ICRP and European Basic Safety Standards have been set up (Stewart et al. 2012; Boal and Pinak 2015), which have also been transposed into national law with a new annual dose limit of 20 mSv (Table 1) (International Commission on Radiological Protection 2007). Unfortunately, accurate estimates of the lens dose within fluoroscopic interventions are hampered by several obstacles and new techniques for dosimetry purposes are not yet routinely available (Kato et al. 2019).

Table 1. Occupational dose limits (ICRP 2007).

Region	Dose limit
Total body dose	20 mSv per year (50 mSv per year; in 5 successive years not >100 mSv)
Eye lens	20 mSv per year
Local skin dose	500 mSv per year
Hands, lower arms, feet, ankles	500 mSv per year
Lifetime occupational dose (exceptions possible)	400 mSv

Current dose limits of occupational exposure in Germany.

In regard to stochastic effects, X-ray exposure is a known risk factor for the induction of various malignancies, such as nervous cell tumors. Data from the Life Span Study cohort of atomic-bomb survivors suggest a threshold below 1 Sv for radiation-induced brain tumor development (Yonehara et al. 2004). In regard to interventionalists, reports on brain tumor manifestation with a predilection within the more exposed left hemisphere have also risen concern (Roguin et al. 2012). However, a profound evaluation, especially concerning prolonged low-dose exposure, and a sufficient follow-up, are difficult. Klein et al. reviewed several studies and case reports on this issue concluding that a causal relationship of brain tumor induction among interventionalist through exposure within fluoroscopic procedures seems ‘suggestive, but by no means conclusive’ (Klein et al. 2009).

For a profound and better understanding of underlying mechanisms of deterministic and stochastic radiation damage after interventional procedures, some studies shifted the focus toward radiobiological effects. Cytogenetic testing found increased frequency of chromosomal aberrations and micronuclei in lymphocytes of patients as well as increased DNA damage and distinct alterations in gene expression profiles after interventional fluoroscopy procedures (Basheerudeen et al. 2017; Visweswaran et al. 2019). Despite these insights, the exact extent of a potential contribution of the IR-associated radiation exposure to stochastic effects remains unresolved (European Society of Radiology 2011). Individual risk assessment in this context is limited not only by a lack of knowledge regarding further radiobiological cues, especially concerning shortcomings of the often applied linear no-threshold model (Tharmalingam et al. 2019), but also by the complex dose reconstruction characteristics for interventional procedures (Falco et al. 2018).

Patient dose levels in complex interventions

Complex interventions with expectably high dose burdens include several procedures, like transjugular intrahepatic portosystemic stent shunt (TIPSS), hepatic chemoembolization, thoracic or abdominal endovascular aortic repair ((T-)EVAR), mechanical thrombectomy, percutaneous vertebroplasty or kyphoplasty and pelvic interventions (Jaschke et al. 2020). In the following, EVAR and neuro-interventional embolization are discussed in more detail.

Regarding EVAR, treatment is often accompanied by high patient doses with mean DAP values of 153,000 cGy*cm² and occasionally, in the case of complex fenestrated EVAR procedures, peak skin doses amount up to >5 Gy over a 6 month period (Kuhelj et al. 2010; Kirkwood et al. 2015). Interestingly, more recent data show considerably lower doses in EVAR (mean DAP 14,700 cGy*cm²; mean cumulative air kerma dose at skin entrance of 0.107 Gy) (Hertault et al. 2018), most likely underlining the potential of dose reduction by means of modern technical development and radiation protection measures. At the same time, occupational exposure of the attending medical staff during aortic repair remains non-negligible (Monastiriotis et al. 2015). As an example for realistic dose burdens, calculated maximum effective doses for the operator of up to 0.345 mSv (0.235–0.757 mSv) during complex fenestrated or branched EVAR procedures have been reported (de Ruiter et al. 2018).

Next to aortic interventions, sophisticated neuro-interventions potentially come along with high exposure levels to both patients and medical professionals. Due to the exposed area under investigation, patient’s skin, hair, brain and eye lenses are particularly at risk of radiation-induced damage (Jaschke et al. 2020). In this context, studies reported on calculated doses for the brain ranging from 500 mGy (Sanchez et al. 2014) up to 45 Gy and for the skin of up to 5 Gy, in the latter case resulting in cutaneous radiation damage after intracranial AVM embolization (Mooney et al. 2000). In addition to lens damage in medical staff, the patient’s eyes are exposed to an even greater extent during neurointerventions with eye lense doses >500 mGy in 16% of neuro-interventional procedures and a maximum dose burden up to 2 Gy (Sánchez et al. 2016).

Radiation protection measures

General management

The easiest way to reduce X-ray exposure to both patient and medical professionals is by omitting unnecessary procedures. Therefore, radiologists must always consider feasible alternatives (e.g. ultrasound-guided interventions). General principles of radiation protection – which should be second nature to every interventionalist – must be obeyed as well. Exposure time must be kept as short as possible, distance must be kept from the patient, as scattered radiation accounts for the greatest part of staff exposure and radiation dose is inversely proportional to the square of the distance, and appropriate shielding must be used (Kim 2018). Furthermore, the utilization of state-of-the-art equipment significantly contributes to dose savings (Busse et al. 2018). These measures and conditions should be supplemented by regular education and training in radiation protection for optimal handling of dose reduction techniques and to preserve awareness of the medical staff as recommended by the European Society of Radiology (2011).

Protection equipment

A variety of protection equipment is firmly established and routinely used during interventional procedures, aiming to reduce exposure levels of the staff. As depicted in Figure 1(a,b), these include personal protection clothing as well as mobile and table-based shielding. Protection aprons and vests with a lead equivalent of 0.35 mm and thyroid shields with a lead equivalent of 0.5 mm proved to accomplish a dose reduction of 72.4–80%, respectively (Koenig et al. 2019). Meanwhile, vest extensions for protection of the humerus head and lateral thorax have become commercially available as well. Next to the optimization of protected body areas, alternative X-ray shielding material, such as gadolinium or other metals, promises a higher comfort based on less weight and even better protection factors for certain energy levels (Uthoff et al. 2014; Kazempour et al. 2015). Based on the evidence for radiation-induced cataracts within interventionalists, protection glasses or visors have emerged in recent years (Vano et al. 2013; Parikh et al. 2017) and have also been included in governmental recommendations and regulations (European Commission 2014; Loose et al. 2020). The use of these protection devices can lead to a reduction of dose to the lens of up to 89% caused by lateral entrance of scattered radiation or scattered radiation emitted from the interventionalist (Galster et al. 2013). Both limitations regarding scattered radiation may be overcome by the combined use of lateral shielding of the glasses or a visor in combination with a protection cap (Koenig et al. 2017). The usage of lead caps has additionally gained popularity by reported elevated brain cancer risk in medical staff attending fluoroscopic interventions (Rajaraman et al. 2016). With a lead equivalent of 0.5 mm, various caps are highly effective regarding radiation protection (Karadag et al. 2013; Koenig et al. 2019). As another frequently exposed body region, the interventionalist’s hands often absorb higher dose levels, especially during complex procedures like EVAR (de Ruiter et al. 2021). In order to provide protection, lead- or metal-based gloves have been used for several years and proved to be highly effective by means of direct dose reduction to the hand (Koenig et al. 2019). On the contrary, the positioning of protection gloves into the direct X-ray beam should strictly be avoided, as it can lead to automated dose modulation with resulting higher dose burdens for the patient (Pasciak and Jones 2014). Furthermore, deficits in tactile sense need to be overcome to obtain general acceptance among interventionalists. New lead-free approaches could pose an alternative, at least regarding the sense of touch and protection against scattered radiation (Kamusella et al. 2017).

Figure 1. (a) Modern angiographic suite with ceiling-mounted transparent acryl-glass lead shielding, protection barrier, over-/under-table lead shielding. System with roboter mounted C-arm and modern flat panel detector. (b) Minimal personal protection equipment for angiographic interventions; Glasses (0.75 mm Pb), thyroid-gland protection, vest and skirt/apron, cap (all 0.50 mm Pb); recommended additional protection for humerus and lateral chest not shown.

Technical measures

Several technical measures are implemented in most IR-suites significantly contributing to dose reduction in modern procedures. An overview on this is given in Table 2 and Figure 1(a). By table-mounted shielding (including over-table extensions and pivot function) scattered radiation emitted from the patient can be reduced up to 64% (Koenig et al. 2019). In line with this, ceiling-mounted shields (lead equivalent ≤0.5 mm) and protection drapes placed on the patient facilitate similar reduction of radiation burden for the interventionalist from 50 up to 96.7% for neck and eye as well as up to 96% for the thyroid gland (Koenig et al. 2019). Modern IR suites also come with a broad spectrum of technical dose reduction applications which should be used by default. For instance, by lowering the pulse rate from 10 to 4 pulses per second a decrease in radiation dose of 60% for patient and staff can be achieved without sacrificing diagnostic image quality in most cases (Teichgräber 2018). The additional utilization of filters for beam hardening and collimators with lead shutters for field-shaping as well as automatic tube voltage modulation during interventions also reduce dose up to 95% (Adamus et al. 2016) and should be stringently applied (Mogensen et al. 2020). Picture enlargement (zoom) with geometric magnification techniques should only be used if absolutely necessary or should be replaced by digital zoom options (Hasegawa et al. 2020). Modern soft- and hardware solutions with high resolution large-sized displays and computational resources provide numerous image processing and illustration facilities, such as virtual collimators, ‘care position’ or ‘last image hold’, preventing the need for repeated fluoroscopy and concomitantly an increase in dose. These technical capabilities enable the application of lower tube currents or lower pulse rates without deteriorating diagnostic quality. Furthermore, fusion of other data sets like CT or MRI within the IR suite can also make fluoroscopic imaging within the planning of an intervention obsolete to some extent (Böckler 2020). Modern flat-panel detectors or roboter attached fluoroscopy systems also pose a possibility for further dose reduction for patients as well as medical staff (Becker et al. 2017).

Table 2. Dose reduction measures (selection).

Measure	Dose reduction
Shielding
Table	<64%
Ceiling mounted	50–96.7%
Personal protection equipment	70–89.3%
Operational
Pulse rate (10 to >5 p/s)	50%
Filtering + collimator + low-dose protocol	<95%

Selection of relative dose reduction potential by different measures and combination. Data adapted from Adamus et al. (2012), Meisinger et al. (2016), and Koenig et al. (2019).

Dosimetry

Personal dosimetry for measurement of occupational exposure underlies strict official regulation in many countries and a dosimeter must be worn by each member of the medical team during every interventional procedure. However, international recommendations are not uniformly transposed into national regulations and, therefore, effective dose calculations and national recommendations for dosimetry differ in detail (Miller et al. 2010; Cousins et al. 2011; Loose et al. 2020). As defined by the German radiation protection regulations, dosimetrical measurements of each professional are assigned to a unique individual number, comparable to a social security number, and are centrally administered. By doing so, monitoring and managing occupational radiation exposure can be ensured for the entire work life averting potential excesses of occupational dose thresholds (Table 1) (Grunert 2019). Regarding the optimal positioning of the dosimeter, a placement underneath the protection vest at the level of the breast pocket is recommended, whereas deviate positions have an negative impact on dose reconstruction (Rigatelli et al. 2016). Yet, some authors recommend wearing two or more dosimeters on different places, in particular near to the eye lens (Clerinx et al. 2008; Bartal et al. 2014; Neto et al. 2017). Film badge dosimeters have been introduced in the early 1960s and are still most frequently used dosimetric device. As an alternative, thermo-luminescence-based dosimeters are approved for routine use (Haninger et al. 2016) and for distinct measurements of organs like the eye lens (Ciraj-Bjelac and Rehani 2014). In addition to these devices, electronic dosimeters represent another promising alternative featuring direct readability of dose levels and dose rates, which is a clear advantage of this technique (Vano et al. 2011; Koenig et al. 2019).

Besides dosimetry of the medical staff, the measurement of patient exposure is mandatory for risk assessment and quality control as well. In clinical routine, a direct measurement of the DAP is performed and peak skin dose as well as effective dose can be calculated (Toivonen 2001; Faulkner et al. 2005).

Organizational approaches

The above-mentioned measures can only tap their full potential when well-understood and routinely applied by the medical staff (Bartal et al. 2016). National and international regulations, a quality assurance program, standard operating procedures and guidelines can help to achieve this goal (Miller et al. 2010; Tsapaki 2020). Radiation protection must be visible within the IR-suite or operating room, e.g. by real-time display of administered DAP and calculated peak skin dose on the monitor. This way, the operator can directly read the applied radiation dose during every intervention with respect to the according reference levels. Furthermore, IR staff needs to be trained on a regular basis (Bartal et al. 2014), ideally in a realistic simulator training (Jaschke et al. 2020). The regular use of collimators in elective and calm procedures might transfer to a natural utilization during emergency interventions. Practical implementation of specific procedures within the workflow range from the selection of a distinct c-arm angulation to reduce scattered radiation exposure for the operator (Albayati et al. 2015) to staff members routinely leaving the IR-suite during short high-dose applications like cone-beam CT (Schulz et al. 2012). Even subtle adaptations, such as calling out to the interventionalist before performing nursing tasks and subsequent brief interruption of fluoroscopy during these tasks leads to reduced exposure of the assisting medical team (Komemushi et al. 2014). In Germany, the assistance of medical physic experts in high dose applications and the implementation of a dose management strategy is mandatory in many cases (Walz et al. 2019). Eventually, the management of unintended and accidental exposures above certain trigger levels is part of radiation protection as well and already implemented in national regulations (Jaschke et al. 2020; Loose et al. 2020).

Conclusions

Advancements in the field of IR have clearly transformed the treatment of several diseases. The importance as well as therapeutical possibilities of interventional procedures is meanwhile undisputed in view of steadily increasing examination numbers. At the same time, interventional procedures often cause high dose burdens for patients as well as the medical professionals. Several studies and reports on this show severe effects due to the associated radiation exposure. In order to prevent excessive exposure – and to keep dose levels as low as reasonably achievable – several technical and organizational measures for radiation protection can be combined and applied. In due consideration and by utilizing all these possible measures on a regular everyday basis, we can tap their full potential for dose reduction. In addition, consistent education and training of the medical staff as well as state-of-the-art equipment and procedures are key to optimal radiation protection for both patients and medical professionals. Upcoming developments for further dose reduction and radiation protection measures in IR embrace a combination of technical developments of X-ray tubes and detectors, radiation protection equipment as well as ongoing adaption of organizational measures by updated guidelines and regulations, altogether helping to further minimize radiation exposure and to optimize radiation protection in IR.

Disclosure statement

All authors declare no conflict of interest.

Additional information

Notes on contributors

Hanns Leonhard Kaatsch

Hanns Leonhard Kaatsch, MD, is a resident in Radiology and a Post-Doctoral Researcher of Radiobiology at the Bundeswehr Institute of Radiobiology, Munich, Germany.

Julian Schneider

Julian Schneider, MD, is a Consultant Radiologist at the Bundeswehr Central Hospital, Koblenz, Germany.

Carolin Brockmann

Carolin Brockmann, MD, is a Professor of Neuroradiology and Consultant Radiologist as well as Neuroradiologist at the University Medical Center Mainz, Germany.

Marc A. Brockmann

Marc A. Brockmann, MD, M.Sc., is a Full Professor of Neuroradiology and Chair of Department of Neuroradiology at the University Medical Center Mainz, Germany.

Daniel Overhoff

Daniel Overhoff, MD, is a Consultant Radiologist at the Bundeswehr Central Hospital, Koblenz, Germany.

Benjamin Valentin Becker

Benjamin Valentin Becker, MD, is a Consultant Radiologist at the Bundeswehr Central Hospital Koblenz, Germany.

Stephan Waldeck

Stephan Waldeck, MD, is a Consultant Radiologist und Neuroradiologist and Head of Department of Radiology and Neuroradiology at the Bundeswehr Central Hospital, Koblenz, Germany.