Radiation Protection during Hybrid Procedures: Innovation Creates New Challenges

ABSTRACT: Background. The cooperation between interventional cardiologists and cardiothoracic surgeons has expanded the spectrum of treatment modalities for patients with congenital heart disease. These hybrid techniques have created new challenges, one of which being the provision of adequate but practical radiation protection. This study evaluates the use of a lightweight radiation protection drape (RADPAD®) that may be suitable for shielding during hybrid procedures. Methods. To simulate a pediatric patient, an 8.7 liter water-filled tub was placed on an X-ray table and exposed to 10-second cine acquisition runs. Radiation exposure was measured at twelve specified locations around the table using a model with three different levels of radiation protection: no shielding, shielding using a traditional 0.35 mm lead-equivalent apron, and shielding using the 0.25 mm lead-equivalent RADPAD. Results. The traditional lead apron and the RADPAD significantly reduced the amount of radiation dose when compared with no shielding. The standard lead apron provided slightly greater radiation protection than the RADPAD (0.000064 radiation absorbed dose [rad] vs. 0.000091 rad; p = 0.012). The measured rad was significantly higher on the right side of the table, and the measured radiation dose decreased significantly with increasing distance from the table. Conclusions. The RADPAD has been shown to function as an efficient shielding device, even though it does not quite match the protection that can be expected from a standard lead apron. It complies with regulatory radiation protection requirements and its lightweight and sterile use make it particularly useful during hybrid procedures in the operating room. J INVASIVE CARDIOL 2009;21:437–440 The term “hybrid procedure” describes the intraprocedural cooperation between interventional cardiologist and cardiothoracic surgeon. The spectrum of hybrid procedures performed in the treatment of patients with congenital heart disease has increased considerably over the last 10 years. It includes a diverse spectrum of procedures such as completion angiograms after cardiothoracic surgery,1 hybrid balloon pulmonary valvuloplasty in premature infants,2 intra-operative stent placement for stenotic vascular lesions3 and hybrid palliation of patients with hypoplastic left heart syndrome.4 Fluoroscopy and angiography are essential imaging modalities to facilitate these hybrid interventions. However, while the use of these modalities has become commonplace within a cardiothoracic hybrid operating room, suitable lightweight and practical radiation protection that also satisfies regulatory requirements remains nonexistent. The RADPAD® (Worldwide Innovations & Technologies, Inc., Overland Park, Kansas) is a commercially available sterile, lead-free, primarily bismuth-based disposable radiation protection drape (Figure 1) that was originally developed to reduce the exposure of staff to scatter radiation.6 This study evaluates its potential use as a customized radiation protection drape that can be utilized during hybrid procedures. Materials and Methods The study was conducted within a custom-designed hybrid cardiac catheterization laboratory with a fixed installed C-arm (Toshiba CFB 5-Axis biplane system, Toshiba America Medical Systems, Inc., Tustin, California). Institutional review board approval was obtained and local procedures for retrospective record review and patient confidentiality were followed. To simulate the torso of a small child/infant, a plastic container (depth 10 cm, length 36 cm, width 22 cm) was filled with 8.7 liters of water, which closely resembles the effective human mass density. A 4 inch Kelly clamp was placed in the center of the container to add scatter and to facilitate centering the flat-panel detector. The table height was set at 40 inches from the floor, with a 2 inch foam mattress placed underneath the plastic container. To simulate staff, an intravenous pole with a height of 6 feet was utilized with a hanger at the top, which held either a standard lead apron, a sterile gown cut to the shape of a lead apron with two RADPAD drapes taped to its front, or no shielding material at all. The pole was placed at twelve predefined locations around the fluoroscopy table (Figure 2). These locations were chosen to simulate typical intraprocedural positions of the physician and staff members during hybrid interventions and included position to the right of the table, to the left of the table and at the head of the table, each with distances of 0, 2, 4 and 6 feet from the table. Radiation exposure was measured in rad (radiation absorbed dose) using the Unfors EDD-30 (educational direct dosimeter) that was placed behind the shield (or no shield) just below collar level. The automated settings used for simultaneous straight AP and lateral cine acquisitions are listed in Table 1. The exposure was measured at each of the aforementioned twelve locations, using no shielding (NOSHIELD), shielding with a standard lead apron (LEAD), and shielding using the RADPAD (Figure 2). Three acquisitions were used for each phantom location and shielding method. Statistical analysis. Basic descriptive variables (mean, median, standard deviation and range) as well as all statistical tests were calculated for continuous variables using StatsDirect software (StatsDirect Ltd, Cheshire, United Kingdom). Variables were evaluated for the presence of a normal distribution using the Shapiro-Wilk test. The measured radiation exposure was compared between different shielding methods (LEAD, RADPAD, NOSHIELD), as well as between different table locations (head, left, right) using the non-parametric Wilcoxon signed rank/matched pair test. Table distance and radiation exposure were compared using Kendall’s rank correlation. All tests were performed at a = 5%. Results Table 2 shows median radiation exposure measured in rad for each of the three shielding methods. The measured radiation exposure was significantly lower when comparing either standard lead apron (p = 0.0005) or the RADPAD (p = 0.0005) with measurements obtained without radiation protection. Radiation exposure tended to be higher when comparing the RADPAD to a traditional lead apron (p = 0.012). Combining left, right and head locations at a 2-foot distance from the table, the median radiation exposure without a shield was 0.0014 rad, compared to the RADPAD, with 0.00012 rad, and the lead apron, with 0.000088 rad. There was no statistically significant difference between radiation exposure measured at the head of the table or at the left side of the table (p = 0.428). However, the measured rad was significantly higher on the right side of the table when compared to the left side (p = 0.0068), or the head (p = 0.0024). There was a significant correlation between distance to the table and measured dose (NOSHIELD, p = 0.0018; RADPAD, p Discussion Nurses, technicians and physicians working in a catheterization laboratory are usually sufficiently aware of and accustomed to the requirements of radiation protection. However, this does not equally apply to staff in the operating room, where the concepts of fluoroscopy and angiography are usually not part of day-to-day management routines. Furthermore, not all radiation protection mechanisms are easily transferable and suitable to the operating room environment. Federal guidelines and Ohio (and other state) law state that a minimum of 0.25 mm lead equivalent is needed for adequate radiation protection during procedures.7 Traditional lead aprons, including those made of lead-equivalent material, are bulky and heavy, even though the weight has improved over the last 10 years.8 Lead aprons remain the most important radiation protection in the catheterization laboratory and are usually worn underneath a sterile gown. Historically, the need for fluoroscopy within the operating room was rare and usually limited to occasional postoperative angiography. These images were frequently acquired with staff members stepping away from the operating room table during image acquisition. However, in contrast to many other personnel, cardiothoracic surgeons cannot easily step out of the operating room during image acquisition. These procedures are often performed with the patient still on cardiopulmonary bypass, and in addition to angiography, may include the delivery of hybrid therapies that can improve procedural outcomes.2,3,9 Figure 4 illustrates a typical example of a hybrid procedure in a 5-month-old infant with hypoplastic left heart syndrome who had previously undergone hybrid Stage I palliation, which is a combination of bilateral pulmonary artery banding and patent ductus arteriosus (PDA) stent placement. The infant then underwent comprehensive Stage II palliation, which is a combination of a bidirectional Glenn, debanding of the pulmonary arteries and PDA stent removal, as well as Damus-Kay-Stansel anastomosis with aortic arch reconstruction. Prior to coming off cardiopulmonary bypass, an angiography was obtained within the superior vena cava, which documented a stenosis/fold of the left pulmonary artery. Intraoperative hybrid stent delivery led to complete relief of this stenosis (Figure 4). This example clearly illustrates the need for adequate radiation protection for the cardiothoracic surgeon, as well as any staff involved in these hybrid interventions. However, the total fluoroscopy time during hybrid procedures is usually very short in comparison to the overall duration of the surgical procedures, and requiring surgeons and staff members to wear a standard lead apron throughout a 6-hour operation is impractical. Wearing a lead apron for a prolonged period of time has been associated with a variety of orthopedic problems in the interventional community,10 which is an unnecessary hazard to the cardiothoracic surgeon. Similarly, it is not always feasible for the surgeon and staff to de-scrub during a procedure in order to put on a lead-apron. The RADPAD may be able to overcome some of the impracticalities associated with standard lead aprons. It has been used in a variety of specialties ranging from urology to interventional radiology and electrophysiology.11,12 It was originally designed to protect staff members from scatter radiation by “lying directly on the patient and creating a ‘shadow’ of minimal scatter for the staff to stand in, thus reducing the scatter radiation by 50%.”6 While this benefit may not be sufficient to replace the lead aprons used in the setting of a cardiac catheterization laboratory, it does meet the 0.25 mm lead-equivalent requirements for direct personal protection, and its modified use may serve as adequate protection during hybrid procedures, which are usually very short and have associated fluoroscopy times of less than 5 minutes. Our results have clearly shown a significant reduction of radiation exposure when using the RADPAD, even though there was a slightly higher dose when compared to a traditional lead apron. Not surprisingly, the radiation dose was higher at the right side of the table, which is closest to the lateral X-ray camera. The RADPAD is very lightweight, and as sterile, single-use material, it can easily be clipped onto the surgical gown during radiation exposure and then removed once the hybrid procedure is completed. Potential modifications of the RADPAD may even allow its incorporation into the surgical gown, which could be worn throughout longer surgical/hybrid procedures. While the RADPAD has a variety of potential benefits through its use as a shielding device during hybrid procedures, it is important to emphasize that radiation protection during hybrid procedures is not solely limited to the “shielding” of the cardiothoracic surgeon and staff. Our data have again shown that some of the greatest reductions in radiation exposure can be achieved by increasing the distance from the radiation source. This is particularly important for staff who may not be needed at the table during image acquisition. Educating operating room staff regarding the fact that the radiation dose can be reduced to a quarter simply by doubling the distance from the radiation source — termed the “Inverse Square Law” — is essential when introducing the regular use of fluoroscopy into a new environment. In addition, the surgeon and interventional cardiologist should strive to limit the use of fluoroscopy and angiography to a dose as low as reasonably achievable (ALARA) without impacting on the diagnostic yield. Study limitations. The model used does not reflect the varying patient sizes and constitutions that are encountered in a children’s hospital. In addition, the number of dose measurements obtained at each location was limited, and its statistical accuracy could be improved upon by obtaining a larger series of measurements. Furthermore, the distance measurements were taken from the edge of the catheterization laboratory table, rather than from the center of the radiation source, which makes it difficult to demonstrate the “Inverse Square Law” using our data. Conclusion The RADPAD has been shown to function as an efficient shielding device, which leads to a significant reduction in radiation exposure. It complies with regulatory radiation protection requirements, and its light weight and sterile use make it particularly useful during hybrid procedures in the operating room. Further data on its regular use during hybrid procedures are needed. _________________________ From aThe Heart Center, Nationwide Children’s Hospital, Columbus, Ohio; bthe Department of Pediatrics, The Ohio State University School of Medicine, Columbus, Ohio; and cthe Department of Cardiothoracic Surgery, The Ohio State University School of Medicine, Columbus, Ohio; and cthe Ohio State University School of Nursing, Columbus, Ohio. The authors report no conflicts of interest regarding the content herein. Manuscript submitted February 10, 2009, provisional acceptance given March 13, 2009, final version accepted March 30, 2009. Address for correspondence: Ralf J. Holzer, MD, MSc, FSCAI, Assistant Director, Cardiac Catheterization & Interventional Therapy, Assistant Professor of Pediatrics, Cardiology Division, The Ohio State University, The Heart Center, Nationwide Children's Hospital, 700 Children's Drive, Columbus, OH 43205. E-mail: Ralf.Holzer@NationwideChildrens.org

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