While strikingly beneficial to the healthcare community, fluoroscopically guided interventions (FGI) come with occupational-related risks. The geometry of the fluoroscopic tube and the staff's close physical location create concern for excessive radiation exposure to those workers. Many interventionalists have documented injuries due to inadvertent exposure to X-rays. While it is an accepted working hazard, it can be mitigated with proper planning and best practices.
Many factors are considered when evaluating the risk of radiation exposure for interventionalists. The stochastic and deterministic effects are carefully weighed in every decision in the FGI procedure room. The patient's needs always come first, and the intervention staff can act accordingly to protect themselves from radiation exposure. The physical location of the staff inside the room can change based on the fluoroscopic tube geometry, radiation protective equipment worn, and the room's design. Not only is the safety of the staff inside the room considered, but so is the safety of those outside or who may enter the room during radiation exposures.
Introduction
Fluoroscopy-guided intervention (FGI) diagnostic procedures are performed when noninvasive procedures are inadequate to answer a clinical question. Some procedures are easily performed with simple imaging equipment and require little radiation doses, while others require an appropriately equipped operating room using specialized equipment. Many FGI procedures require physicians and support staff to position themselves beside the patient. These individuals are frequently irradiated while performing their duties. Workers in FGI procedures are in a small population of monitored healthcare workers who could experience high levels of radiation exposure.
Irradiation of these workers is considered an unavoidable part of providing healthcare during FGI procedures. Like other public service professionals, including the fire and police forces, some risk is simply part of the job description for medical professionals. Risks to medical personnel, such as severe illness or death, are acceptable by society if avoiding these risks would result in patients not receiving appropriate medical care. However, radiation risk management is of vital importance for medical procedures. Proper education, training, awareness, and personal protective equipment for radiation exposure are integral to the safety of FGI personnel.
Primary and secondary radiation are the two ways FGI personnel receive exposure during a procedure. Primary exposure comes from a person's body parts placed in the primary radiation beam between the X-ray tube and imaging receptor. This exposure is not common to FGI staff and should only be acceptable when it is critically important to the patient's health. Secondary radiation exposure in FGI suites comes from leakage radiation of the X-ray tube and scattered radiation from the patient’s tissue in the primary beam. Typical operating techniques yield a leakage rate of 0.001 to 0.01 mGy h-1 at 1m, and scattered radiation levels are generally 1 to 10 mGy h-1 adjacent to the patient.
The ALARA principle should be in place without sacrificing patient safety or clinical procedures and increasing workers' non-radiation risks. An example of non-radiation risk is spinal injuries related to wearing inappropriately heavy lead aprons. For FGI procedures, ALARA is satisfied with the design, selection, and use of equipment, equipment replacement schedule, and day-to-day working procedures. Implementing these items maximizes the procedure's net benefit. All workers involved in FGI procedures manage their radiation dose (ALARA) while providing appropriate patient care.
Effects of Occupational Exposure During FGI Procedures
Occupational exposure during FGI procedures can cause many different effects on the human body depending on age, sex, anatomy, location of exposure, and many other factors. These effects may manifest themselves immediately or after many years or decades. Consideration of special precautions for each worker during the FGI procedure ensures the lowest possible chance of adverse occupational health effects due to radiation exposure.
Stochastic effects of radiation exposure typically are unmanifested for years to decades after the exposure. The age, gender, life expectancy, and health status of the individual determine the risk of stochastic effects. Deterministic effects manifest within days to weeks after the interventional therapeutic procedure. Interventionists, nurses, technologists, and all staff in the procedure room are at risk of developing stochastic effects, primarily increased risk of cancer. Deterministic effects occurring in individuals as a result of modern practice are rare and typically due to insufficient training, not using available protective equipment, or poorly maintained equipment. An example of a deterministic effect of radiation exposure is radiogenic eye changes resulting from FGI procedures (cataracts). Studies have also reported hair loss on the legs of an interventionist (below the margin of the lead apron) resulting from years of occupational exposure.
Special precautions must always be put in place when a radiation worker declares a pregnancy. The highly volatile nature of an embryo and fetus generates different concerns depending on the stage of pregnancy. Further information on monitoring the dose of declared pregnant workers is described later.
How Interventional Staff Can Reduce Exposure Based on the Use of Fluoroscopy
The use of radiation PPE, engineered shielding, and dose measurement all help prevent or monitor radiation exposure and are fundamental tools for radiation protection from FGI procedures. However, the most critical radiation safety solution is a general understanding of X-rays and education on their nature, along with the best practices. Proper training, procedures, equipment usage, and personnel placement are as crucial as any manufactured and designed product.
While a procedure is in progress, each person in an FGI-procedure room must have radiation protection training based on FGI best practices. All radiologists in the United States receive training in radiation physics, radiation biology, and radiation safety as part of their radiology residency. They must also pass an exam on these topics to receive certification from the American Board of Radiology. Interventional cardiology fellows receive training in radiation physics and safety, and the board examination in interventional cardiology includes questions in these subject areas.
All pertinent staff should be well-versed in the facility's policies and procedures for a time-critical, urgent, or emergent situation where an additional dose is acceptable. Advanced provision exists to exceed an annual occupational dose limit.
Conditions under which an annual occupational dose limit for an interventionist or assisting staff member may be exceeded |
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Table from NCRP 168 |
FGI interventionalists can lessen their radiation exposure by using the fluoroscopy unit as little as possible as long as it does not compromise or is a detriment to the patient's health. Fluoroscopic units are engineered to have multiple exposure modes to lessen the radiation to the patient and, by association, the FGI staff. On many fluoroscopic units, radiation may be emitted continuously or in pulses. Options for different pulse rates may be available to the operator. A variable pulsed rate should be used for FGI procedures, but continuous exposure is acceptable for low-dose FGI procedures. FGI staff need to be cognizant that pulsed modes may degrade or lessen the ability to visualize the procedure. A balance of lowering radiation exposure and adequately performing the procedure should be constantly evaluated. Interventionalist experience may govern the exposure to patients and staff. It has been observed that less experienced interventionalists tend to use more time and radiation to perform procedures than more experienced interventionalists.
Fluoroscopic gantries designed for FGI procedures can rotate the X-ray tube and image receptor at a fixed point called the isocenter. This point is where the patient's anatomy of interest is placed during FGI procedures. Backscattered radiation is the primary secondary radiation source during FGI exposure. Much radiation does not penetrate the patient’s tissue but is reflected. With this in mind, an X-ray tube positioned underneath the table minimizes scattered radiation to the chest and head of the interventionist. Subsequently, the most intense scattered radiation is directed away from the operator’s head. Fluoroscopes are available with the x-ray tube, typically over the patient (over table systems). Additional caution for the patient and staff is vital when these systems are used for FGI procedures. These should be avoided because of the highly scattered radiation directed at the head and neck of the interventionist.
Tube collimators influence patient and staff exposure during an FGI procedure. Virtual collimation furnishes a graphical display of the collimator blade's position on the clinical image while the collimator blades are adjusted. This feature eliminates patient irradiation while adjusting the collimator. Regulations require that the X-ray beam is closely collimated with the image receptor so that primary radiation outside of the visible image is minimal.
The physical size and shape of the intervention room and the location of the FGI staff inside the room can help reduce exposure to the staff. Generous procedure room size is beneficial because it allows staff space to safely maneuver and function during the procedure and allows them to maximize their distance from the patient as long as it is rational with their duties. Interventionalists whose presence is close to the patient should incorporate tools and methods to allow for increased distance.
The interventionist generally stands close to the patient to manipulate interventional devices and is located between the hips and knees on the patient's right side. When using a c-arm in a lateral position, staff should position themselves on the image receptor side of the patient if possible. When the c-arm is in the vertical orientation, positioning the X-ray tube under the table will place higher scattered radiation areas toward the floor so that the interventionist's hand, neck, and eye receive less radiation. An isodose curve shows that exposure on the image receptor side of the patient is approximately a factor of 10 less than that on the x-ray tube side.
Personnel performing clinical monitoring of patients during an FGI procedure should be located in the control room whenever possible. However, clinical requirements may demand that staff responsible for anesthesia, clinical monitoring of patients, or other duties be physically located in the FGI procedure room during the procedure. An intercom between the control and procedure room allows staff to remain outside the room until needed.
Radiation Safety Equipment Used in FGI Procedure Rooms
Each person in an FGI procedure room should be provided with appropriate radiation protective equipment while a procedure is initiated. Not all forms of radiation protective equipment are required at all times. Some staff may be allowed the privilege to utilize more comfortable and less cumbersome radiation PPE due to their duties and location during the FGI procedure.
When the X-ray beam is energized, all FGI procedure room personnel not behind a radiation barrier should wear radiation-protective garments (lead aprons, thyroid shields, and lead-equivalent glasses). Lead or lead-equivalent aprons should protect against radiation without excessive weight. The apron weight can pose a substantial ergonomic risk to its wearer. Apron weight can be lessened by removing lead and replacing it with other materials with the same or better attenuation for scattered radiation from fluoroscopic beams.
0.5mm lead/lead-equivalent aprons are currently the standard, but thinner lead aprons may provide adequate protection. A 0.5 mm lead equivalent garment attenuates over 95% of incident radiation, protecting body organs and lowering the radiation exposure to the wearer. Based on the calculations from dual personal dosimeters (one in front of the apron and one behind the apron), a 0.3 mm lead/lead equivalent apron will result in radiation exposure that is only moderately higher (7-16%) than a 0.5 mm lead/lead equivalent apron.
Thyroid shields are lead/lead-equivalent garments typically worn with a protective apron around the neck. They are designed to protect the thyroid from radiation exposure. For younger workers, the thyroid gland is relatively sensitive to radiation-induced cancer. However, the cancer-incidence risk depends on the age at irradiation, with minimal risk after 30 years for males and 40 years for females.
Radiation-attenuating surgical gloves are available to interventionists to reduce hand exposure. However, reducing dexterity from radiation-attenuating surgical gloves may increase fluoroscopy time. Attenuating surgical gloves provide a minimal reduction in hand dose for FGI procedures. Suppose hands-in attenuating surgical gloves are placed on the primary beam during fluoroscopy. In that case, they will intercept the automatic brightness control sensing area: thus causing the air-kerma rate incident on the patient's skin to automatically increase, resulting in an increase in dose to the interventionalist’s hands and the patient.
It is well documented that a high eye dose is possible for interventionalists performing FGI procedures. Injury to the eye's lens from occupational exposure has been reported, specifically for an over-table x-ray tube configuration. Lead-lined eyeglasses have been shown to reduce eye dose. 0.25 mm lead-equivalent glasses attenuate about 90% from the front, and standard glasses range from 30-35%. Plastic lenses attenuate minimal radiation. The interventionalists and others normally turn their heads from the primary beam to view the fluoroscopy monitor during exposure. With this in mind, protective eyewear should provide shielding for side exposure, using either side shields or a wraparound design.
Mobile lead-lined barriers are an acceptable form of whole-body radiation protection. These are typically 0.5 to 2 mm lead equivalence, large, and frequently transparent. Ancillary personnel who do not need to be next to the patient but are required to remain within the procedure room will find these as a convenient alternative to cumbersome lead aprons. They are also useful for interventional staff to step behind during high dose rate digital image acquisition series. If personnel can remain completely behind a protective barrier during the procedure, wearing a lead apron is generally unnecessary.
Room layouts that permit easy and comfortable access to mobile and fixed shielding increase the likelihood of their use. The barrier design should be based on the maximum expected occupancy by any individual in all locations behind protective barriers during the work week.
Highly specialized FGI equipment may come with table-mounted and ceiling-mounted lead or lead-equivalent protective barriers to protect the interventionist from radiation exposure. Table-mounted shields typically consist of lead drapes mounted to the side of the patient table. The typical lead equivalent thickness is 0.5mm and protects the lower extremities of staff from radiation scatter. Mobile c-arm fluoroscopes typically do not have this feature. Ceiling-mounted protective barriers are typically 0.5mm lead equivalent. They are mounted to the ceiling using articulating arms. These are transparent and designed to shield the upper body of the interventionist. The contoured lower sections of the ceiling-mounted protective barrier are designed to be positioned around the patient.
Staff members working in FGI procedures should know when radiation is produced to optimize their radiation protection. Different fluoroscopy and image acquisition sounds can alert interventionists and staff that radiation is being generated. However, some fluoroscopy equipment does not emit noise during the production of X-rays. In these rooms, staff cannot rely on an audible indication of X-ray production. When sound is not emitted while the X-ray tube is energized, an amber light can be illuminated on the fluoroscopy unit. Even when the fluoroscopy unit utilizes audible and visual signals, an announcement before exposure should be made to allow staff to protect themselves.
Radiation Safety For Personnel Outside of FGI Procedure Rooms
Radiation exposure from FGI procedures is not limited to those inside the procedure room. Much of the patient's scattered radiation can potentially expose personnel outside of the room as well. Precautions and safety features are implemented to minimize exposure to those outside the room.
Some situations require personnel to enter the FGI procedure room during a procedure. X-ray indicator lights or signs at the procedure room entrance indicate that the X-ray equipment is in use or that the X-ray beam has been activated. These will alert staff that radiation is present and precautions should be taken if room entry is required.
Door interlocks that end x-ray production are not permitted at any entrances to FGI-procedure rooms. Door interlocks that prevent x-ray production when opened eliminate dose to personnel who open the procedure room door while exposure is initiated. However, the imaging disruption during a critical portion of the procedure could harm the patient. This may require the patient to be repeatedly imaged with X-rays or incorrect interventional device positioning. The dose rate at the procedure door during fluoroscopy will generally be less than 0.1 μGy s-1. With this low exposure level, the potential patient harm does not justify the installation of door interlocks.
When planning an interventional facility, careful attention to workers' radiation exposure from the planning process's beginning can help reduce occupational exposure. The walls, floor, ceiling, doors, and windows surrounding an FGI procedure room should provide sufficient attenuation to reduce the radiation in outside spaces to an acceptable level. A busy cardiac angiography suite usually does not require more than 1.5mm lead equivalent barriers to reduce scattered radiation levels below the shielding design goal of 1 mGy y-1 (air kerma) at 3m from the center of the imaging field of view.
Dose Measurement Considerations for Workers in FGI Procedure Rooms
To accurately assess compliance with occupational dose limits, the personal protective equipment used by each individual in the FGI procedure environment must be considered.
The dose distributions in these staff members are always highly non-uniform. The causes of these nonuniformities include nonuniform radiation fields, differential shielding of different body parts from the radiation, and scattered radiation produced within the irradiated individual. Due to their positioning next to the patient during exposures, there is a large difference between the exposure to the left and right sides of the interventionist. Typically, the left side of the interventionist is exposed more than the right side.
The personal dosimeter must be worn in the same location to avoid artificial variations in dose estimates from one monitoring period to another. Two personal dosimeters are highly recommended for each person involved in FGI procedures. One should be worn under the protective apron, and a second should be worn at neck level above protective garments. A single personal dosimeter worn at neck level above protective garments may be used in the FGI procedure environment. A single personal dosimeter worn under the protective apron cannot be used in the FGI-procedure environment.
In the United States, a 50 mrem monthly limit (equivalent dose) for an embryo and fetus (excluding medical and natural background radiation) is put in place once the pregnancy is declared. The shielding provided by a standard protective lead apron is typically sufficient to protect the embryo and fetus from exposure to staff involved in interventional procedures. Once the pregnancy is declared, a personal dosimeter is worn under the apron by the pregnant worker at waist level from the date the pregnancy is declared until delivery. This dosimeter overestimates the actual dose to the embryo and fetus because radiation attenuation by the mother's tissues is not considered.
Monitoring of equivalent dose to the eye's lens should be performed with the dosimeter placed either at the collar level outside any radiation protective garment or near the eyes. Estimates of effective dose and equivalent dose to the skin, hands, feet, and eye lenses received during FGI procedures should always consider the personal protective equipment used in individual cases to properly assess compliance with occupational dose limits. Investigations should occur if personal dosimeter readings for an individual are substantially above or below the expected range for that individual's duties.
Conclusion
Radiation exposure to occupational workers is a decisive part of all FGI procedures. However, other significant decisions need to be made during a procedure. Since the patient is exposed to far more radiation than the staff, their needs are carefully weighed, determining the long-term benefits gained due to the procedure and the long-term effects of radiation exposure. The safety of the interventional staff should not be the primary concern but is still a factor in providing patient care. A well-trained FGI staff knows the effects of radiation exposure and how to avoid excessive exposure while providing the best care to the patient possible.