Proper Shielding Technique in Protecting Operators and Staff From Radiation Exposure in the Fluoroscopy Environment

J INVASIVE CARDIOL 2021;33(5):E342-E343. doi:10.25270/jic/21.05342

Radiation shielding can provide effective protection from scatter radiation during cardiac interventional procedures, but the individual shields must be thoughtfully and precisely arranged to achieve optimum protection.¹ Since the employment of fluoroscopic shielding continues to be operator-dependent,^2-4 its effectiveness varies considerably.  Current catheterization laboratory design requires the operator to coordinate the placement of the x-ray tube, the image intensifier, and both ceiling and table-mounted shields to obtain the best images and protect those who work in the lab. Proper positioning by the primary operator is considered voluntary even though the occupational hazards of unnecessary exposure affect the health of the entire staff in the working environment.

Scatter radiation is the principal source of radiation exposure to interventional physicians and fluoroscopy suite staff.^3,4 Scatter radiation is secondary radiation spreading in various directions when a beam interacts with objects, causing the x-rays to be dispersed. In the catheterization laboratory, the patient’s body is the primary object that deflects radiation, causing it to distribute around the room. The operator is at highest risk consequent to relative proximity to the patient and x-ray beam.

Standard catheterization suite shielding combines a movable ceiling suspended and fixed table-side shielding to significantly reduce scatter radiation exposure.⁵ Minimizing the area of the vertical gap between these shields minimizes scatter radiation “leakage” through the gap and reduces operator exposure. This gap is accentuated by moving the shield away from the patient’s body surface and further away from the access site. Therefore, the best protection from scatter radiation is provided when the upper body shield is located relatively far from the scatter source and close to the physician to minimize the effective size of the gap in protection that is created by the patient contour cutout.³ The most common error is positioning the shield close to the image detector and x-ray tube and directly over the patient  (ie, farther from the operator). Although this position is commonly taught as being the correct one, in fact, positioning the ceiling shield closer to the x-ray tube to maximize its radiation “shadow” is less effective than using the shield as one would use an umbrella in wind-driven rain, that is, as close to the operator as possible.¹ When correctly placed, shields can provide at least 80% protection from scatter at all table elevations.⁴ Use of accessory soft extensions along the bottom edge of the upper body shield helps to maintain contact between the patient and shield, thereby minimizing the amount of scatter directed toward the physician.

In this issue of the Journal of Invasive Cardiology, Murat and colleagues⁶ evaluate how real-time dosimetry providing on-the-spot radiation exposure feedback motivated modifications in the use of shielding equipment available in the catheterization laboratory. During the first 36 days, dosimetry was measured but the staff had no access to the results, while in the second phase, knowledge of their exposure motivated behavioral changes sufficient to produce a 60% reduction. Despite a variation in baseline levels, this feedback resulted in better use of protection devices in the highest-volume operators. Real-time dosimetry is therefore  an effective teaching tool to motivate better shielding technique to reduce staff radiation exposure in the cardiac catheterization laboratory.

Most importantly, Murat et al⁶ demonstrate how much more can be done practically to protect staff and ourselves once attention is called to the subject. Correct shielding practices are well known, but actually employing them once the case is underway sometimes takes lower precedence. To maintain effective protection during procedures, the upper body shield requires continual repositioning when the patient table height is adjusted, when the table is moved longitudinally or laterally, or when it must be moved to avoid collision with the x-ray system for steep caudal angles. Because the upper body shield must be specifically placed by the physician and often is moved during the procedure, it must be continually readjusted.  The sense of nuisance this creates must be consciously overcome; although we know intellectually that shielding works and is important, it is an annoyance to be concerned with it when our minds are focused on the patient. That the most advantageous shield positioning can have a greater than 4-fold relative reduction in scatter radiation exposure supports its use even when inconvenient, and suggests that learning to coordinate multiple shields should be among the fundamental principles taught in every interventional cardiology training program.^7-9

The basic radiation protection principles of radiation safety are time, distance, and shielding. Time means limiting exposure to the minimum amount possible. Distance means staying as far from radiation sources as possible as a best practice. The intensity of radiation generally follows the inverse-square law, meaning that it decreases with the square of the distance from the source. Moving twice the distance away from a source of radiation reduces the intensity of exposure by a factor of (one-half)² or one-fourth the value. Unfortunately, increasing the distance from the scatter source may be awkward for operators, who are working close to the patient.

Beyond time and distance, making use of effective shielding is the best approach to managing exposure to radiation. Radiation shield protection products are lead-lined glass or latex/plastic. Shielding means placing something that will absorb radiation between the source of the radiation and the area to be protected. The concept of shielding is based on the principle of attenuation, which is the loss in intensity of a beam of radiation as it traverses through barrier material. Attenuation is the result of interactions between x-ray and matter from a combination of absorption and scatter. The differential absorption increases as kVp decreases.  Lead is particularly well-suited for lessening the effect of x-rays due to its high atomic number, which refers to the number of protons within an atom; a lead atom has a relatively high number of protons along with a corresponding number of electrons. These electrons “block” the x-ray photons that are projected through a lead barrier by absorbing their energy. The degree of protection can be enhanced by using thicker shielding barriers. Because of the heavy weight of lead, layers of bismuth and some lightweight synthetic materials are often used in garments.^10,11

The meticulous application of established radiation protection techniques is essential to minimize exposure. Personal protective garments, eyeglasses, and head protection are necessary accoutrements. Collimation of the beam to the specific area being treated is another effective measure, as the larger the amount of tissue the beam is penetrating, the greater the amount of scatter radiation. Selecting judicious table height and angulation to minimize scatter is sensible practice; using high kVp and low mAs techniques reduces scatter and also improves image quality. Mobile lead shields of at least 0.25 mm lead equivalency are recommended to be used by anyone working near the table during fluoroscopy procedures when possible.

Despite proof that shielding is an effective remedy and prudent practice, its correct use is not mandatory and remains operator-dependent. The future interventional laboratory must be designed so that radiation safety is not predicated on the voluntary cooperation, sensitivity, and education of operators, but rather is constructed into the design of the laboratory.^7,12 We may need an automated mechanism to place the shields correctly, or a surrounding shell around the patient.  More expansive and encompassing lead shielding systems are commercially available.¹³

Moreover, attitudes about personal protection must change; this ought not be a matter of courtesy, but rather a required labor practice.⁷ Common physician opinion is that more rules and regulations are the last thing we need; yet, here is an example of a behavior that appears amenable to change, but never does. Interventional cardiologists must accept the challenge to adopt healthier attitudes and new technologies for the reduction of occupational hazards.^7-9 The study by Murat demonstrates that we are teachable if given positive feedback in a manner that reminds us what adequate protection entails in real time.

From the University of California, San Francisco, Cardiology Section, San Francisco, California.

Disclosure: The author has completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The author reports no conflicts of interest regarding the content herein.

Address for correspondence: Lloyd W. Klein, MD, University of California, San Francisco, Cardiology Section, 505 Parnassus Ave, M1177A, San Francisco, CA 94143. Email: lloydklein@comcast.net

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