INTRODUCTION — In addition to the patient, healthcare workers are exposed to significant amounts of radiation during cardiovascular imaging procedures. With advancing technology, the realm of procedures being performed percutaneously is steadily expanding. The increased anatomic and technical complexity of these procedures often requires longer fluoroscopy and image capture time and leads to greater radiation exposure to the patient and interventional laboratory staff . In addition, these procedures are exposing new groups of health care workers, including echocardiographers and anesthesiology and operating room staff, to radiation exposure from fluoroscopic imaging while assisting with these procedures. It is imperative that healthcare workers involved in these procedures be aware of the radiation exposure and are provided with the tools necessary to protect and monitor themselves .
This topic will present radiation risks related to occupational exposure in diagnostic and interventional imaging suites, the role of dosimetry, and tools for minimizing radiation exposure to health care workers. Other related topics, including discussions of radiation injury and radiation exposure in cardiovascular imaging, are presented separately. (See "Clinical manifestations, evaluation, and diagnosis of acute radiation exposure" and "Radiation-related risks of imaging" and "Radiation dose and risk of malignancy from cardiovascular imaging".)
RADIATION RISK — Exposure to ionizing radiation can lead to tissue reactions (formerly known as deterministic effects) or stochastic effects (a stochastic effect represents an outcome for which the probability of occurrence, rather than severity, is determined by the dose). An example is radiation-induced carcinogenesis. (See "Radiation dose and risk of malignancy from cardiovascular imaging".)
When standard radiation protection tools are used in the cardiovascular interventional lab, doses to the operator and staff do not typically approach thresholds of tissue reactions and the principle risks to consider are the stochastic risks of induced cataract formation and cancer .
Cataracts — The lens of the eye is one of the most radiosensitive tissues in the body [4,5]. In spite of the well documented history of radiation-induced cataract, there is still considerable uncertainty surrounding the relationship between dose and radiation cataract development . Studies of exposed human subjects suggest that there is no clear threshold dose for cataract formation. It also appears that the latency period is inversely related to the exposure dose.
In one study, 50 percent of interventional cardiologists and 41 percent of cardiac catheterization lab staff had significant posterior subcapsular lens changes, which are typical of ionizing radiation exposure . Similarly, increased incidence of radiation-associated lens changes were noted among interventional cardiologists in a French multicenter observational study . Use of protective eyeglasses can substantially mitigate this risk.
Cancer — Although controversial, radiation exposure from medical imaging, including that incurred by health care workers, is thought to be associated with an increased risk of cancer (see "Radiation dose and risk of malignancy from cardiovascular imaging"). For example, there has been substantial debate about the incidence of brain cancer in interventional cardiologists [9-11]. A case cohort study of interventional cardiologists with brain cancer revealed that 86 percent of the brain tumors in which location was known originated on the left side of the brain . This finding was deemed significant because, in the general population, brain tumors occur with equal frequency in the left and right hemispheres and interventional cardiologists typically stand with the left side of their body closest to the radiograph source.
MONITORING RADIATION EXPOSURE — All staff working in the interventional fluoroscopy suite should be monitored to quantify radiation exposure. The primary tool for estimating radiation dose to staff are personal dosimeters.
Quantities and units — Dose limits to health care workers are either reported as equivalent dose, which reflects the dose in a specific organ or tissue, or as the effective dose, which reflects whole-body exposure. Both of these quantities are expressed in units of Sieverts. These quantities cannot be measured directly and have to be estimated based on data from personal dosimeters. The equivalent dose is calculated by multiplying the absorbed dose in an organ or tissue by a tissue weighting factor, which reflects the sensitivity of that organ or tissue to the effects of radiation. The effective dose is calculated by summing the equivalent dose to all exposed organs/tissues.
Dosimetry — The International Council on Radiation Protection (ICRP) recommends use of two personal dosimeters in the interventional lab: one worn on the trunk of the body inside the apron, and the other worn outside the apron at the level of the collar or the left shoulder . The collar badge can be used to estimate dose to the surface of unshielded skin and the lens of the eye. Data from both dosimeters can be used to estimate the effective dose, using the following equation (where Hw represents dosimeter values at level of waist under the apron and Hn represents dosimeter values from above the apron at the neck) :
Effective dose = 0.5 Hw + 0.025 Hn
This and other commonly used formulas to calculate effective dose based on dosimeter values typically overestimate the actual effective dose. For safety reasons, these formulas are designed to avoid underestimation of the effective dose at the expense of overestimating the dose by up to 100 percent or more . Hand doses can also be monitored using a ring badge .
Occupational dose limits — Occupational dose limits have been defined by the ICRP and the National Council on Radiation Protection and Measurements (NCRP) [3,16]. In the European Union, the limit for effective dose is 100 mSv over a five-year period with no more than 50 mSv in any one year. This limit is described somewhat differently in the United States, with a limit of 50 mSv in any one year and a lifetime limit of 10 mSv multiplied by the individual’s age in years.
A busy interventional operator using good technique and proper protective equipment typically receives 2 to 4 mSv per year [1,17-19]. Even if one assumes a relatively high workload of 1000 angiographic procedures per year, the annual effective dose limit of 20 mSv will rarely be exceeded . The World Health Organization recommends investigation when the monthly effective dose reaches 0.5 mSv or dose to lens of the eye reaches 5 mSv . The radiation safety officer or a qualified medical physicist should communicate directly with the worker to determine the cause of the high dose and to suggest methods to keep the worker’s dose as low as reasonably achievable . Investigation of a high personal dose starts with verification of the validity of the badge reading, including proper placement of the badge (eg, placing badge over versus under apron) and ruling out use of badge by other staff. If the reading is thought to be valid, the next step is to investigate any changes in work habits that could explain the increased dose, such as starting a new type of procedure or changes in procedure technique or equipment settings. Once the cause of a high personal dose has been identified and appropriate feedback and education is provided to the worker, implementation of the suggested changes to work practices should be monitored.
Dose limits during pregnancy — The NCRP recommends limiting occupational radiation exposure of the fetus as low as reasonably achievable but no more than 5 mSv during the entire pregnancy and 0.5 mSv per month of the pregnancy . The ICRP recommends a lower limit of occupational radiation exposure to the fetus of <1 mSv.
In order to ensure limiting occupational radiation exposure to the fetus, monthly monitoring of the radiation exposure using a dosimeter badge under the lead apron at waist level is recommended.
RADIATION PROTECTION — The greatest source of radiation exposure to the operator and staff in the interventional lab is scatter from the patient . In general, any measure that reduces radiation exposure to a patient will also reduce operator and staff exposure. The goal of occupational radiation safety is to minimize exposure to the operator and staff without impeding the procedure or compromising the patient’s safety. The cardinal principles of occupational radiation protection are time, distance, and shielding. These three principles are discussed below.
Time — Decreasing exposure time, the time for which the radiograph beam is on, is an essential component of radiological protection. It can be achieved by reducing fluoroscopy time and by reducing the fluoroscopy dose rate.
Distance — The relationship between distance from radiograph source and radiation exposure follows the inverse square law; doubling the distance from the source reduces radiation exposure to one-fourth of the original dose. It is important when positioning oneself to understand that scattered radiation intensity is highest at radiograph beam entrance side of the patient. The operator should be positioned on the side opposite the tube when possible.
Shielding — Shielding should occur on multiple levels: architectural, equipment-mounted, and personal protection devices . Architectural shielding is built into the walls of the room in which imaging occurs.
Equipment-mounted shielding includes table-suspended drapes, ceiling-mounted shields, and lateral table-mounted shields . In addition, rolling and fixed shields made of transparent leaded plastic can be used to provide extra protection for personnel in the interventional lab. Disposable, lightweight, sterile radioprotective shields in drape or pad form are available, which are placed on the patient, outside of the beam path, after the field has been prepared . These shields have been shown to substantially reduce operator dose [23-25].
Personal protective devices include lead aprons, thyroid shields, eyewear, and gloves. Aprons and thyroid shields should always be used in the interventional lab. Aprons are available in one-piece and two-piece vest/skirt options, as well as pregnancy aprons that can accommodate the enlarging abdomen. Aprons typically have a lead-equivalency of 0.25 to 0.5 mm . Those with a lead equivalency of 0.25 mm allow approximately 10 percent of the radiation from radiographs to pass through, whereas the transmission ratio with 0.5 mm lead equivalency is only about 2 percent [26,27]. Ergonomic injuries related to personal protection devices should also be considered [14,16,28]. Proper fitting of aprons can reduce ergonomic hazards. Radiation-attenuating materials such as bismuth oxide and barium sulfate, rare-earth metals, and composites including lead, tin, tungsten, and barium are increasingly being used as alternatives to lead in personal protective devices in order to reduce their weight. Two-piece (skirt/vest) wraparound aprons can reduce the risk of back injury by distributing the apron’s weight and are recommended by the International Council on Radiation Protection [2,13]. Lead aprons should be properly placed on hangers and should not be folded, creased, or crumpled in any way. They should be inspected visually and fluoroscopically before being put into use and periodically thereafter to detect damage to the protective material [13,27].
Radiological protection for the eyes is essential for interventionalists [13,29]. Ceiling-suspended protective shields are effective at protecting the entire head when used properly. Leaded eyewear can also significantly reduce radiation dose to the operator’s eyes [30,31]. Protective eyeglasses should fit properly and should provide shielding for side exposure, using either side shields or a wraparound design .
Operators should generally avoid placing their hands in the primary fluoroscopy beam. If the operator’s hands will be in the primary radiation beam, leaded gloves may not help reduce exposure due to the increase in radiation intensity when any shielding is placed in the primary beam [13,20]. Use of radioprotective bismuth oxide-containing lotion may be useful in this setting . However, the most effective approach to protecting the operator’s hands is to keep them out of the primary beam.
Robotic-assisted intervention is an innovation that can lead to dramatic reductions in operator radiation exposure . This approach can also reduce orthopedic injuries related to personal protection device use. Robotic systems allow the operator to perform procedures remotely, away from the patient’s bedside. Seated in a radiation-protected cockpit, the operator uses digital controls to robotically manage catheters, guidewires, and devices. An initial trial assessing this technique suggested that it is safe and effective and associated with a 95.2 percent reduction in radiation exposure to the primary operator . Subsequent studies evaluating the application of this technology to increasingly complex coronary anatomies have also been encouraging [34,35].
ROLE OF HOSPITAL/FACILITY — Application of radiation safety principles requires education and training of operators and staff. Radiation safety training should be a routine part of credentialing of all personnel working in the interventional lab. The hospital/facility should provide ready access to appropriate protection equipment and also establish dosimetry monitoring programs and enforce compliance with these programs. The International Council on Radiation Protection recommends that the advice of a medical physicist be sought to interpret monitoring results . Moreover, all fluoroscopy machines must meet design and use standards approved by regulatory bodies and regional radiation protection programs.
TIPS FOR INTERVENTIONAL LAB STAFF — The primary operator is responsible for managing radiation in the interventional lab from the beginning to the completion of the procedure [13,16,20,36,37]. While radiation should never be administered without a clear indication, procedures cannot be terminated solely on the basis of the radiation dose administered . When high-dose radiation has been administered, the operator must balance overall benefit and risk when deciding whether to pursue further imaging and/or intervention.
The following practical tips can help reduce radiation exposure to the patient and operator:
●Try to position yourself in a low scatter area. In general, scattered radiation is most intense on the radiograph tube side of the gantry and lower on the side of the image receptor [38-40]. Scatter radiation to the operator is highest in the left anterior oblique position, particularly with cranial angulation .
●Use shielding, including ceiling-suspended shield, table-suspended screen, and personal protective devices (apron, thyroid collar, and leaded eyeglasses) to the fullest extent possible.
●The ceiling-suspended shield should be placed as close to the patient as possible. Positioning this shield as close to the image receptor and as low on the patient as possible, tilted slightly away from the operator in order to cast the largest shadow possible on the operator, has been shown to dramatically reduce operator eye dose [30,42].
●Use a radioprotective pad or drape when appropriate. These pads should not be visible in the fluoroscopic image. If they are, the result will be an increase in patient dose .
●Avoid placing hands in the primary radiation beam.
●Minimize use of fluoroscopy. "Beam-on time" should only occur when the physician is looking at the monitor.
●Use low-dose-rate fluoroscopy settings, including low frame-rate fluoroscopy when possible.
●Minimize use of cine mode. Store radiograph fluoroscopy when possible.
●Collimate the radiograph beam as tightly as possible.
●Use magnification as little as possible.
●Review all existing imaging information ahead of time to plan the interventional procedure.
●Obtain appropriate training in radiation protection.
●Wear your dosimeters and know your dose.
The amount of scattered radiation is affected by multiple factors including patient size, gantry angulation, patient position, filtration, fluoroscopic settings, and use of shielding. Larger patient size, high-dose fluoroscopy, and steep gantry angulation can substantially increase the magnitude of radiation scatter. Proper shielding is particularly important in these scenarios.
TIPS FOR ECHOCARDIOGRAPHERS AND ANESTHESIA STAFF — Percutaneous structural heart procedures, such as transcatheter aortic valve replacement, mitral valve repair, and left atrial appendage closure, require the support of echocardiography and/or anesthesia staff in the interventional lab. As the echocardiographer has to be positioned immediately adjacent to the patient, they are also in close proximity to the radiograph source. Moreover, they are typically positioned at the head of the table or on the left side of the patient, where ceiling- or table-mounted shielding is not usually available. As such, it is particularly important for echocardiography and anesthesia staff to use personal protection devices. Use of mobile-leaded plastic shields positioned between staff and the radiograph source can provide added protection.
Performing echocardiography on patients shortly after a nuclear medicine study (such as nuclear myocardial perfusion imaging) is another potential source of radiation exposure to echocardiographers . Scheduling the echocardiography before the nuclear imaging study can prevent such exposure. In situations where echocardiography has to be done shortly after a nuclear medicine study, the potential radiation exposure should be considered when assigning staff to avoid recurrent exposure to the same echocardiographer or to pregnant staff .
TIPS FOR NUCLEAR MEDICINE STAFF — Radiation doses to nuclear medicine and nuclear cardiology staff are in general lower than those to interventional fluoroscopy staff, and it is highly unusual for nuclear medicine staff to approach regulatory limits, as specified above. The nuclear medicine workers with the highest radiation doses are typically those with considerable exposure to positron emission tomography (PET) radiopharmaceuticals . Dose to staff from technetium 99m is greater than that of other single-photon emission computed tomography (SPECT) radiotracers such as gallium 67 and iodine 131 . Mean daily effective dose for PET technologists is approximately 14 microSv, and effective dose per minute of close contact (<2 m) with a radioactive source is approximately 0.5 microSv/min . The use of dose-reduction techniques that implement the fundamental principles of time, distance, and shielding, such as employing a semi-automated injector, patient video tracking  and using shielded syringes [47,48], can lower doses to staff. As for interventional fluoroscopists, the use of personal radiation monitors is essential for all workers in nuclear medicine. Radiation protection garments may be elected for use by pregnant SPECT workers but are not useful in PET due to the higher-energy photons.
RECOMMENDATIONS OF OTHERS — In addition to reports and guidelines referenced within the text above, the Heart Rhythm Society has published an expert consensus statement on electrophysiology laboratory standards, which includes a section on radiation safety .
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Non-ultrasound imaging in pregnancy".)
SUMMARY AND RECOMMENDATIONS
●When standard radiation protection tools are used in the diagnostic and interventional lab, doses to the operator and staff do not typically approach thresholds of immediate tissue reactions. The principle risks to consider are the long-term risks of cataract formation and cancer. (See 'Radiation protection' above.)
●All staff working in the interventional fluoroscopy suite should be monitored to quantify radiation exposure. The primary tools for estimating radiation dose to staff are personal dosimeters. (See 'Monitoring radiation exposure' above.)
●Use of personal protection devices, including apron, thyroid collar, and protective eyeglasses, is necessary in the diagnostic and interventional laboratory. (See 'Radiation protection' above.)
●Operators, laboratory staff, and workers with radiopharmaceuticals should be familiar with methods to reduce dose to the patient and staff. (See 'Radiation protection' above.)
●The cardinal principles of occupational radiation protection are time, distance, and shielding. (See 'Radiation protection' above.)
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