Minimizing Occupational Radiation Exposure in the EP Lab: Theories, Implications, and Recommendations That Potentially Extend EP Team Longevity

Abstract

Atrial fibrillation (AF) is the most common type of heart arrhythmia worldwide. The number of patients with AF is rising exponentially in part due to a rapidly aging population. With the advent of contact force catheters, outcomes of AF ablation continue to improve. However, treatment of AF with catheter ablation can increase radiation exposure for patients and operating room staff. The demand for this procedure is rising in proportion with the elderly population and the availability of better ablation tools.

This increases the lifetime radiation exposure of electrophysiology (EP) laboratory workers. Recurrent exposure to ionizing radiation, even at low doses, can accumulate long term and produce health risks. If not used properly, lead aprons provide incomplete shielding against x-ray exposure and contribute to chronic orthopedic issues in nearly 60% of laboratory staff.^1,2 All radiation dose reduction protocols based on the standards of ALARA (as low as reasonably achievable) to minimize x-ray exposure are essential to maintain the EP team’s longevity. The goal of this 2-part analysis is to provide electrophysiologists and EP staff with a basic understanding of the biology of ionizing radiation, the mechanism of injury induced by x-ray, and simple tools for reducing x-ray exposure. Practical x-ray exposure reduction recommendations, including the choice of protective aprons as well as the use of shields and fluoroscopy settings, will be reviewed in part 1. Our approach to reducing or preventing fluoroscopic use during catheter ablation of AF will be discussed in part 2 of this article series.

Key words: atrial fibrillation, electrophysiology, ionizing radiation, occupational exposure, protective aprons, pulmonary vein isolation, x-ray

Introduction

Fluoroscopy is a tool that uses x-ray to produce live images that are useful during image-guided cardiac procedures, such as pulmonary vein isolation (PVI), for the management of AF. Fluoroscopy generates images using a form of ionizing radiation. In contrast to visible light, which does not penetrate tissue, x-rays can penetrate the human body, providing a means to visualize structures not visible to the naked eye. In its simplest form, fluoroscope consists of an x-ray source and a fluorescent screen, between which a patient is placed. X-rays are directed through the body to generate an image. The intensity of x-ray energy decreases due to scatter and absorption (attenuated) as it passes through or reflects off various tissues, forming a shadow of the radiopaque tissue. Images are produced as the unattenuated or mildly attenuated x-rays from these radiolucent tissues interact with atoms giving off energy, some of it in the form of visible light, thus forming images. As x-ray energy passes through tissue, it can also cause harmful biochemical changes to cellular structures including DNA. Radiation injury is determined by the penetration ability of the ionizing radiation used, the portion of the body exposed, the duration of exposure, and the total dose. Tissues and organs consisting of rapidly proliferating cells, such as the skin, eyes, reproductive organs, gastrointestinal tract, and bone marrow, are most susceptible to radiation injury, where there is proliferation of progenitor cells to replace the aging cells lost through senescence. The effects of radiation on these organs can result in damage to the precursor cells and the subsequent inability to replace the older cells, which is essential to the maintenance of tissue structure and function. In this way, exposure to ionized radiation increases the risk of cancer, thyroid dysfunction, skin damage, development of cataracts, and other injury.³ Therefore, electrophysiologists and their staff must not only be experts in cardiac electrophysiology, but they must also understand how to minimize the harmful effects of fluoroscopy to preserve longevity. The EP service (Figure 1) at Owensboro Health Regional Hospital (OHRH) has adopted all dose reduction practices, including appropriate gear, low-dose settings, lower frame rates, pulse duration, detector entrance dose, and increased beam hardening; these practices will be reviewed in part 1 of this article series. In part 2, we will discuss our approach to preventing fluoroscopic use during catheter ablation of AF. This will include a summary of techniques to perform PVI using non-fluoroscopic catheter visualization to create an environment in which the use of lead aprons are no longer necessary.

Biophysics and Basic Nomenclature of X-ray and Fluoroscopy

X-rays are composed of both electromagnetic waves and particles similar to visible light. Unlike light, x-ray possesses higher energy and can penetrate the human body, producing shadows while passing through the x-ray detector on the other side. These images are used by EPs to safely maneuver catheters in the body and the heart. In order to produce a fluoroscopic image, a continuum of x-ray energies is emitted through a point source, the x-ray tube, located below the table that supports the patient. These x-rays are directed towards the image intensifier or detector, located above the patient. The higher the energy emitted by the point source, the deeper it can penetrate the body. The characteristic shadows produced on the monitor result from the electromagnetic radiation released by atoms within tissues in response to the absorbed x-ray energy. Not all the x-rays emitted by the x-ray tube are absorbed. Rather, some of the non-absorbed energy is scattered, which results in not only blurring of the desired images, but also unwanted x-ray exposure to nearby staff members. The high-energy waves and particles from the scattered radiation are capable of stripping electrons from atoms (ionization) of adjacent individuals; ionization results in chemical changes in the well-organized milieu of the cell, disrupting and damaging cells and genetic material.^3,4 Biological injury is divided into 2 categories: deterministic or stochastic. Deterministic radiation damage occurs after a certain threshold quantity is surpassed and the risk grows linearly at increasing doses, while stochastic x-ray injury can occur following a single small exposure so that no threshold value is considered safe. An example of stochastic injury resulting from ionizing radiation is cancer and possibly changes to the eye lens, a pathology known as radiation cataracts.⁵ Deterministic injury most commonly results in skin damage for patients and cataracts in providers and EP laboratory staff. The National Council on Radiation Protection (NCRP) and the International Commission on Radiology Protection (ICRP) have proposed guidelines suggesting that cataractogenesis is a deterministic effect. However, a stochastic cause is feasible since this eye pathology can manifest at lower doses than the set standard.

The biological effect of x-ray absorbed by the body is called the radiation dose or kerma, which stands for kinetic energy released in matter (specifically air). This represents the energy of absorbed radiation by an organ or tissue per unit of mass, measured in milligray (mGy) or Sievert (SV), where 1 mGy is equal to 1 mSv (Figure 2). The amount of radiation that a person is exposed to is calculated by effective dose in millisieverts; this varies by genetics and body mass index (BMI). The effective dose is calculated as a sum of the combined dose of individual organs to obtain a total quantity. Modern fluoroscopy equipment features statistics regarding the amount of radiation exposure to the patient by a measurement referred to as the kerma area product or dose area product (DAP).⁶ DAP is the total amount of radiation delivered to the patient, while air kerma (AK) is the rate of radiation delivered at a specific point. Due to the above-mentioned hazards associated with radiation exposure and the eye pathology manifestation at lower doses than proposed, the ICRP revised its lifetime eye dose threshold for cataract induction to 500 mSv, and the occupational annual dose limit from 150 mSv to 20 mSv y⁻¹ in a year, averaged over 5 years, with no single year to exceed 50 mSv.⁷ Typically, the radiation dose to patients from an AF ablation, during which up to 15-20 minutes of fluoroscopy can be used, is estimated at 19.4 mSv. For the patient, this radiation dose is approximately equivalent to undergoing 830 chest x-rays.⁶

Motivation for Minimizing or Eliminating the Use of Fluoroscopy

According to a retrospective analysis, interventional cardiologists are among the health professionals that are most highly exposed to x-ray. Approximately 25% of current interventional cardiologists are at risk of developing radiation-induced cataracts due to their surpassing the 500 mSv lifetime eye dose threshold set by the ICRP.⁸ The rate of radiation-induced brain tumors among these cardiologists is also troubling, and possibly due to head and neck exposure. Left-sided brain tumors were inexplicably more common in a group of physicians who performed procedures requiring the use of radiation, suggesting a causal relationship between occupational radiation exposure and brain cancer.⁹ The operators’ hands and reproductive organs are other vital structures at high risk of radiation injury, as these are in the direct path of the radiation beam and in close proximity to the point source, respectively. The risk may be even higher for EPs due to the number of complex procedures such as PVIs that generally generate greater x-ray exposure per case, resulting in a higher annual dose received compared with interventional cardiologists. Lead-lined head caps and glasses significantly reduce x-ray exposure by shielding the head and eyes; these should be used without exception. Lead aprons, although helpful, have been shown to contribute to chronic orthopedic issues in nearly 60% of laboratory staff.^1,2 Creating a lead-free environment by building a fluoroless AF program can safely decrease x-ray use as well as feasibly reduce orthopedic problems due to lead aprons.

Magnitude of Exposure

Radiation dose is important from both the patient and staff perspective. From a patient standpoint, this is significant because (1) skin injury can occur from just 2 Gy exposure, and (2) just 1 hour of fluoroscopy time can increase the risk of death from cancer by up to 0.1%.¹ Patients often require multiple procedures, especially procedures to treat left atrial arrhythmias, which adds to their total lifetime radiation exposure. Obese patients, which are not uncommon in our practice, are at even higher risk since they receive higher effective doses of radiation compared to patients that have a normal BMI. The laboratory employee’s exposure is usually only 1 to 2% of the patient’s dose. From an EP lab staff perspective, even though this dose may seem small, it is important because cardiologists and especially EPs tend to be exposed to high cumulative doses of radiation throughout their lifetime, providing them with an estimated cumulative lifetime attributable risk of cancer on the order of magnitude of 1 per 100 exposed subjects.^13,14 Clearly, this is not inconsequential exposure, and we must assume that there is no safe dose. All doses add in determining cancer risk in line with the linear no-threshold model of radioprotection.

Recommendation for Limiting Radiation Exposure in the EP Laboratory

The 3 fundamental theories of radiation protection (increased distance, decreased time, and the use of shielding) should be routinely considered in the daily workflow of every EP laboratory (Table 1). Minimizing radiation exposure can be divided into those processes that the medical staff can implement personally (proper use of protective shielding, education, and surveillance), operator-dependent practices (workflow habits), and EP laboratory configuration (x-ray setting, table and intensifier height, and positioning and system parameters).

Simple Means for Lowering Personal X-ray Exposure

Staff Awareness, Shielding, and Dosimeter Tracking

Staff awareness and tracking are the 2 simplest steps for monitoring and minimizing x-ray exposure. This starts with the correct use of lead shields and accurate dose monitoring with the dosimeter provided to each EP laboratory staff member for their protection and records. Occupational monitoring is essential for the equal safety of cardiologists and laboratory staff members. The ICRP and American College of Cardiology (ACC) recommends 2 personal dosimeters, one worn outside the apron at shoulder or neck height, and the other under the apron at waist height.^15,16 Careful monitoring and tracking ensure that the wearable protection is used as recommended and effective dose is tracked reliably.

Due to close proximity to the x-ray point source, the highest exposure occurs to the operator’s lower trunk. Wearable lead skirts provide the greatest protection to the operator’s reproductive organs and are required at all times. Properly worn lead aprons can reduce the annual effective dose from 46.2 mSv without protective gear, to 3.5 mSv per year with just an apron, and to 1.7 mSv per year when using the combination of an apron and thyroid shield^6,17 (Figure 3). These protective shields provide protection against effective radiation dose to the groin, thorax, and neck, but provide negligible protection against scattered radiation to unprotected areas such as the hands and head (including the eyes). Lead glasses can lower the radiation dose to the eyes by 98% compared to 36% by non-lead glasses, and are highly recommended.^18,19 Lead acrylic face masks provide identical safety for those individuals who wear prescription glasses. The authors find wearing head caps lined with lightweight barium sulfate and bismuth oxide to be comfortable (Figure 3).²⁰ These weigh <130 grams and have been shown to reduce radiation doses to the head and neck by 90%, while preventing orthopedic problems that accompany wearing heavier gear.²¹ Table- and ceiling-suspended drapes also afford significant eye, head, and neck protection, and should routinely be adjusted with C-arm angulations despite the time and effort required for this (Figure 4).^22-24 Lastly, hands are unshielded and are in direct line with the x-ray beam, resulting in up to 1,500 mSv exposure per procedure. Although lead gloves are protective, they can be cumbersome and reduce operator dexterity. Instead, the use of lead-free, radiation-attenuated latex gloves can reduce the radiation dose to the operator’s hands by nearly 60%. Finally, walk-in lead-lined suits are available, which can supply the needed protection without the orthopedic strain. These are preferred by many centers, but can sometimes be cumbersome and challenging to manipulate into position. Due to the size and positioning of these ceiling-suspended systems, we feel that this protection is most useful during ablation procedures rather than during device implants.    

For their personal protection, every staff member should ensure that their lead aprons and thyroid shields have been checked annually through fluoroscopy for cracks and holes. Tracking lifetime x-ray exposure is akin to saving for retirement. Every exposure adds up and should be tracked to ensure an accurate tally of each individual’s dose, just like retirement investments are tracked and grow with time. To ensure precise dosimeter recording, avoid entering a room without a personal dosimeter. Leave a procedure if you are not wearing your own personal protective gear, rather than standing behind someone who is “leaded.” Prior to stepping on the pedal, look around the room to ensure that everyone is wearing their appropriate gear. Any essential staff member not in proper attire is politely asked to suit up or momentarily step out. Care should be taken to ensure that the primary and secondary operators’ hands are not in line of the primary beam prior to using fluoroscopy. These simple measures avoid unprotected exposure and ensure accurate tracking, prolonging the working life of our staff.

Staff Education

Promoting radiation safety is the responsibility of every member of the EP team. On-the-job training to reduce radiation exposure is essential and part of the quality assurance process of every laboratory. Individual staff members should review their own past personal dosimeter results and then choose from the available shielding garments that are appropriate for their workspace. Keep in mind that all protective gear is not equally effective, so choose the gear that will ensure safe and healthy practice. When in doubt, have a low threshold for consulting local medical physicists.

Reducing Fluoroscopy Exposure Through Workflow

Decreasing Radiation Exposure Time

Fluoroscopy should be used as sparingly as possible; it should only be used when an operator is actively looking at the images. Pulsed digital fluoroscopy maintains image quality while reducing exposure by approximately 50% compared with continuous imaging.¹² Fluoroscopic images can be stored in place of cine, since cine increases x-ray exposure by 5X compared to fluoroscopy images. To limit x-ray exposure, fluoroscopy should be implemented in short bursts (rather than continuously) to observe objects in motion when the operator is required to watch the monitor. For example, during implants, experienced EPs can partly rely on intracardiac and ECG signals rather than fluoroscopy to place leads. Once venous access has been obtained, leads can be cautiously guided into the right atrium and ventricle without the use of fluoroscopy. Premature atrial or ventricular contraction suggests that the wire has reached the heart, indicating that it is a safe time to take a quick look as the lead is further advanced. Higher magnification (7″ vs 9″) can increase the dose to the patient by 1.7% as well as increase scatter; therefore, limiting magnification as much as possible is recommended.²⁵ Virtual collimators can reduce the need to adjust collimator blade position, which can reduce exposure.²⁶ Integration of non-fluoroscopic practices to visualize catheters into the workflow allows for the safe performance of complex ablation such as PVI without using any fluoroscopy.²⁴

X-ray Source Distance, Beam Angulation, and Patient Position and Shielding

As previously described, radiation scatter is the primary means of operator and staff exposure. Scatter can be minimized by adjusting the thickness of the x-ray beam, the patient’s position, the distance of the operator from the source of radiation (access site), the fluoroscopic and acquisition settings, filtration, and shielding and gantry angulation.²⁷ Radiation exposure increases with reduced distance from the x-ray beam and angulation such that exposure is higher during device implants while working at the chest, closer to the x-ray source, than during studies, while operating from the femoral area, further from the source. This signifies the importance of using intermittent fluoroscopy. Similarly, adjusting the height of the table to position the patient at the maximal distance from the x-ray tube and the image receptor as close as possible to the patient should be practiced to reduce scatter (Figure 5). Adjusting the table height away from the point source reduced the AK measurements without any effect on DAP. Decreasing AK can reduce the risk of skin injury to the patient as well. Equally important, steep LAO and RAO angulation views should be limited to 30º or less if possible, since steeper angulations can give up to 3 times the dose when compared to <30º angulations.²⁸ Projections of more than 26º have been shown to nearly double the AK measurements compared with fluoroscopy at LAO or RAO projections at <26º. Table-suspended lead drapes should be adjusted when steep angulations are necessary. Additionally, radiation scatter is mitigated when ceiling-mounted shields are placed as close to the patient as possible.²⁹

Decreasing Ionizing Radiation by Changing Settings

Adjusting X-ray Settings and Fluoroscopy Rate

Reduction in fluoroscopic acquisition frame rate from 30 frames per second (FPS) to less than 7.5 FPS is suggested. Most EP procedures can be completed using just 3.5 FPS or even 1 FPS. Fluoroscopy image processing with modern units can compensate for the reduced image quality due to the lower frame rate. Higher frame rates may be necessary while working close to the AV node, such as while mapping and modifying the slow pathway for the treatment of AVNRT. Non-fluoroscopic catheter visualization and mapping techniques can reduce fluoroscopy use during such higher risk cases.

Scatter can be further reduced by collimation to the radiation field and increased use of metallic x-ray beam filters for both fluoroscopy and image acquisition.^11,17

Examination-specific protocols called diagnostic reference levels (DRL) in nuclear medicine are tailored to the patient and specific procedures.³⁰ These guideline levels are intended to standardize the dose of radiation to the patient and staff. The DRL for the specific procedure should not be repeatedly surpassed. Review of technique and remedial action is recommended if the levels are routinely exceeded.⁹

Conclusion

The use of fluoroscopy is helpful in caring for patients with cardiac electrophysiology disorders. X-ray utilization results in ionizing radiation that can be harmful to the patient and the operating room staff, potentially shortening careers. EP teams must take every effort to minimize their own exposure to enhance longevity. The 3 basic principles of radiation protection (increased distance, decreased time, and the use of shielding) should be habitually considered in the daily workflow of every EP laboratory. The lifetime reduction of occupational radiation can be achieved by appropriate staff education, the proper use of wearable protective gear, and exposure tracking with a dosimeter. Vital organs (including the head, eyes, and hands) not shielded by lead aprons can be effectively protected with additional personal and room shielding. Implementing a combination of techniques, including patient and equipment positioning, lowering the frame rate, and decreasing cine exposure will reduce scatter and the overall radiation dose. All these efforts can be implemented without compromising patient safety or outcomes. Part 2 of this review will provide a step-by-step guide on our approach to preventing fluoroscopic use during catheter ablation of AF. 

Disclosures: The authors have no conflicts of interest to report regarding the content herein.

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