Novel Radiation Protection Devices: An Update on Radiation Safety in the Cath Lab

Stimulated by a couple of recent articles on the efficiency of the RADPAD protection drape in reducing operator’s exposure¹ and the effects of shielding on nurses and technologists in the cath lab², I thought it would be a good idea to see what was new and what we should be thinking about to reduce radiation exposure to ourselves, our team, and our patients.  

 

To remind all of us, radiation safety is everybody’s business in the cath lab. While standard teaching about radiation safety is part of every team member’s basic concepts and training, there have been very few major changes in our protective equipment over the years to reduce radiation exposure, other than to employ the standard tableside and mobile shielding. We know that radiation dose is directly related to exposure time, determined by the operator’s visualization needs (i.e., pedal time).  We also are aware that the distance away from radiation source is also a critical determinant of dose: the further, the better. Methods to reduce exposure are summarized in Table 1.  Let’s not forget that significant radiation exposure has the potential to impact the health and well-being of interventional cardiologists and their teams by causing³:

 

Cath lab radiation shielding provides only partial protection depending on location around the table, body heights and imaging angles (Figure 1A-B). Personal protection equipment (PPE) alone has limits and is not sufficient to block all scatter radiation dose to the interventional cath lab staff. No current radiation protection strategy is designed to protect the entire health care team in the interventional cath lab room (Figure 2). We need to account for additional staff locations around the table for transcatheter aortic valve replacement (TAVR), right heart procedures, biopsies and transesophageal echocardiogram (TEE), with operators at the head of the table and very close to a radiation source.  Although novel shield systems have been proposed over the last several years, none have been routinely employed in most laboratories.

 

 

During daily operations, we hope that the circulating cath lab personnel are far enough from the x-ray tube to keep their radiation exposure at very low levels. Unfortunately, we probably do not use these vertical shields enough or some may not believe they actually work. Madder et al² recently looked at radiation exposure among scrub technologists and nurse circulators during cardiac catheterization, emphasizing the impact of using accessory lead shields. Real-time x-ray exposure was collected in 764 consecutive procedures in two phases. In the first phase, standard radiation protection measures were used and in the second phase, standard radiation protections were combined with an accessory lead shield placed between the staff member and the patient. Radiation exposure was then reported as a normalized dose area product. They found that accessory shield use was independently associated with lower dose area product exposure among both technologists (with a 34% reduction) and nurses (with a 36% reduction). The authors determined that the use of accessory shielding was indeed associated with a significant reduction in radiation exposure among nurses and technologists.  

 

 

The RADPAD (Worldwide Innovations & Technologies, Inc.) is a sterile, disposable, lead-free shield placed on the patient’s side and is presumed to minimize operator-received scattered radiation. The efficacy of the RADPAD was compared to a standard treatment with no pad or sham treatment with a pad that had no shielding in it¹ (Figure 3). The sham pad allowed for testing of shield-induced radiation behaviors by the operators. The exposures were compared between the RADPAD, “SHAMPAD”, and “NOPAD” as the ratio between the operator’s exposure and the patient’s exposure in dose area product in mGy/cm². In 766 consecutive procedures, each of the three groups of 255 patients were tested. The RADPAD was associated with 20% reduction of relative operator exposure compared to NOPAD and a 44% relative exposure compared to the use of the SHAMPAD. SHAMPAD with associated with 43% higher relative radiation exposure than procedures with NOPAD (Figure 4). It appears that in daily clinical practice, use of the radiation RADPAD shield reduces the operator radiation exposure compared to with no pad or sham pad, and supports the use of such a device in the cath lab.

 

 

A ceiling-suspended gantry system is available to support a walk-in, lead-lined suit that eliminates the weight of lead aprons on the users. Stress injury due to the weight of lead has been reported by interventionalists. Using TIDI Products’ Zero-Gravity Radiation Protection System (Figure 5), this issue is eliminated. The lead apron has 1-mm lead equivalency protection from the thyroid to groin, about twice the protection compared to standard lead aprons. It also provides 0.5-mm protection where previously there was none available, with front and side protection from direct and scatter radiation. While this system has been available for several years, its adoption has been slow.

 

 

The EggNest-XR System (Egg Medical) is a carbon fiber sled platform with flexible shielding for radiation protection which conforms to the patient’s body to provide effective shielding with full x-ray gantry motion. It is particularly designed to improve shielding for radial, femoral and neck access, with specifically designed flexible shields for head and neck protection. The system lies on top of the x-ray table and includes integrated electrocardiogram (ECG) wiring (Figure 6A-B). Significant reductions in x-ray exposure were demonstrated for each position both above and below the table, as well as around the table with the EggNest-XR System compared to the standard shielding (Figure 7).

 

 

There are three robotic systems currently on the U.S. market that have indications for electrophysiology (EP) procedures, coronary artery procedures, and peripheral artery navigation and intervention. Stereotaxis was the first to introduce a robotic system, followed by the Hansen Sensei Robotic System, both designed for long EP procedures. The Corindus CorPath system gained U.S. Food and Drug Administration (FDA) approval for percutaneous coronary intervention (PCI) in 2012, followed by an indication for peripheral vessels in March 2016. Use of the robotic system permits the remote operation of devices during the cath procedure, thus eliminating exposure. However, confidence in complete independent remote operation for a complex PCI at this time remains low.

 

 

Beyond vertical mobile shields, radiation protection in the lab could be coupled with some novel systems of reducing x-ray system dosage.4 There are new x-ray systems which generate less x-ray rate dose. Manu et al at the Cleveland Clinic Foundation⁵ reported on dose reduction x-ray systems for the pediatric catheterization laboratory. They compared the Megalix tube and amorphous silicon detector to that of the Gigalix tube, a more powerful version of the Megalix tube from Siemens Healthineers. The advancement in tube design was the replacement of the amorphous silicone with crystalline silicone as the photo detector, which decreased electronic noise at the detector level and reduced radiation necessary to obtain images of the same quality. They found that a Gigalix tube and crystalline Si detector decreased radiation dose by 50 to 60% for fluoroscopy and cine acquisition in pediatric patients. This advancement will likely be extended into the adult cath lab.  

 

Reduced frame rates also reduce x-ray dose. Radiologic software programs augment imaging systems to achieve excellent visibility at low x-ray dose levels for patients of all sizes. This unique software helps correct for motion, reduces noise, auto-enhances the image and corrects pixel shift on cine images. In addition, a new x-ray tube (Siemens Healthineers) that uses flat emitter technology enables smaller, square focal spots that may reduce exposure 70 percent, with improved visibility of small vessels and improved image quality.  

 

 

The traditional radiation monitor badges are not very helpful because they only alert the badge’s wearer (a cath lab nurse, tech, or operator) to high levels of radiation well after the fact.⁶ Real-time exposure dosing can be obtained with one of several systems (Figure 8A-B). For example, the RaySafe i2 system (Unfors RaySafe) provides teams the ability to see their personal radiation exposure on an overhead display screen and move their location  or make other changes (i.e., bring in an additional shield) to lower their exposure. The accumulated dose per individual user also is captured and displayed.  

 

 

In the cath lab, the majority of x-ray scatter radiation in any angiographic projection comes from below the mattress top. Angulated views significantly increase staff radiation exposure. Standard shielding provides modest protection for the angiographer positioned at the radial/femoral access sites, but no protection for the remainder of the staff or for procedures with head access. Mobile floor shields add protection for those circulating in the room. There are novel systems soon to be available (like the EggNest-XR System, among others) which can provide significantly better protection for both the physician and the staff in the room, and for all positions around the table. We should continue to work toward reducing radiation exposure and use the best protection operator techniques, methods, and equipment available.