Author + information
- John W. Hirshfeld Jr., MD∗ (, )
- Paul N. Fiorilli, MD and
- Frank E. Silvestry, MD
- Cardiovascular Medicine Division, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania
- ↵∗Address for correspondence:
Dr. John W. Hirshfeld, Jr., Cardiovascular Medicine Division, University of Pennsylvania Medical Center, 11-109 South Pavilion, Perelman Center for Advanced Medicine, 3400 Civic Center Boulevard, Philadelphia, Pennsylvania 19104.
It is well-established that even low levels of exposure to ionizing radiation cause molecular injury in tissues with potentially detrimental consequences (1,2). Radiation-induced stochastic effects are believed to be linearly dose-related with no threshold below which there is zero risk. The evolution of the radiation biology and safety knowledge base led to the formulation of the ALARA principle that states that radiation exposure should always be kept “As Low As Reasonably Achievable.” As understanding of the health implications of radiation exposure has accumulated, standards for exposure limits of occupationally exposed workers have become more restrictive. The current standard, from the 2007 recommendations of the International Commission on Radiological Protection specifies a maximum permissible dose of 20 mSv/year averaged over a 5-year period with no one year exceeding 50 mSv (3). This is a decrease from the prior standard of 50 mSv/year. As further experience with occupational exposure accumulates, it is likely that future standards will specify lower limits.
Invasive and interventional cardiologists constitute a group of physicians, with careers potentially lasting >4 decades, who incur among the largest career occupational exposures. There is uncertainty with respect to what detrimental effects these physicians may experience as a consequence of their exposure. Accordingly, what dose levels may be considered “safe” is not completely clear.
This reinforces the importance of the ALARA principle. Consequently, it is important that this group of physicians employ all available tactics to minimize their occupational radiation exposure. Physician operator knowledge of radiation physics, biology, and safety is the foundation of protective strategies because physicians need to understand the theoretical basis of the tactics to protect themselves. Clinical competency statements in regard to physician knowledge of the subject have been developed and published (4).
Although invasive cardiologists have a long history of dealing with the occupational exposure issue, a new constituency of exposed physicians is emerging. Structural interventional cardiology frequently requires transesophageal echocardiography (TEE) guidance, often employs general anesthesia, and may involve collaboration with cardiovascular surgeons. Consequently, these physician groups, who may not have training in radiation protection, now frequently work in a potentially high-radiation environment and may be subject to considerable radiation exposure.
Findings and the Effect of Shielding
The Crowhurst et al. study (5), in this issue of the Journal, measures the scattered x-radiation exposure received by TEE operators, anesthesiologists, and interventional operators during structural cardiac interventions. It relates exposure magnitude to procedural characteristics and examines the value of protective shielding (5). The authors used instantly downloadable dosimeters to measure the radiation exposure received by all members of the structural interventional team. In the initial 98 procedures, the TEE operator and the anesthesiologist wore protective lead garments but did not have any portable radiation shielding. In this group of procedures, the unshielded TEE operator mean per-procedure exposure (2.62 μSv) was somewhat greater than the first operator’s mean exposure (1.91 μSv; p = 0.101) and substantially higher than the second operator’s (0.48 μSv; p < 0.001), both of whom benefitted from portable shielding. The anesthesiologist, who could be located farther from the radiation source than the other operators, received less exposure (mean 0.48 μSv).
In the subsequent 50 procedures, the investigators utilized a second ceiling-mounted shield for the TEE operator. This resulted in an 82% reduction in the TEE operator mean exposure (2.62 μSv to 0.48 μSv; p < 0.001). Through multivariate linear regression analysis, the authors found that the type of procedure (left atrial device implantation) and fluoroscopic projection (procedures utilizing predominantly right anterior oblique and steep right anterior oblique projections) was independently associated with greater doses to the TEE operator. These findings are consistent with previous measurements of the effect of radiologic projection on the intensity of scattered radiation at a particular location (6).
We congratulate the authors on this important effort toward reducing radiation exposure to TEE operators. Their findings, although documenting the value of additional shielding protection for the TEE operator, have implications for the entire structural heart team. Practices aimed at reducing radiation exposure should be adopted and championed by all members of the structural heart interventional team and by all operators who conduct any sort of x-ray fluoroscopy-guided procedure.
Exposure of Structural Interventional Team Members
The operator exposures measured in the Crowhurst et al. study (5) are consistent with other studies’ findings (7). These values indicate that current operator exposure rates are well below the current International Commission on Radiological Protection maximum permissible dose of 20 mSv per year. In the Crowhurst et al. study, the first interventional operator received a mean dose of 1.91 μSv per procedure (5). A highly active operator performing 500 procedures (of all types) per year would likely accumulate a total annual exposure of approximately 1 mSv—well below the International Commission on Radiological Protection maximum. Nonetheless, as outlined in the preceding text, these values do not justify lack of attention to efforts to reduce occupational exposure further.
Determinants of Operator Exposure
To identify opportunities to reduce radiation exposure, it is important to consider determinants of exposure in an x-ray fluoroscopic environment, which fall into 3 main categories:
1. Magnitude of total x-ray exposure used (determined by equipment calibration, operating mode, and beam-on time). This parameter is best measured by the Kerma area product, which reflects the total amount of radiation released.
2. Distance from the radiation source (radiation intensity decreases as the square of the distance from the source).
3. Shielding (0.5-mm lead-equivalent shielding intercepts 90% to 95% of incident radiation in the diagnostic energy range).
Shielding to decrease operator exposure
Previous studies have also demonstrated that TEE operators receive substantial radiation exposures during fluoroscopic procedures (8). Several unique issues arise with respect to protecting the TEE operator. By necessity, the TEE operator must stand in close proximity to the x-ray source. In addition, the TEE operator generally stands with his or her back to the x-ray source, and the back of the lead apron typically has a thinner layer of lead for protection (typically 0.5 mm on the front and 0.25 mm on the back). Lastly, mounted shields can pose a challenge to the TEE operator’s ability to access the patient and manipulate the TEE probe effectively. Given these challenges, the American Society of Echocardiography recommends that echocardiographers participating in fluoroscopically guided procedures should wear personal protective equipment when exposed, wear radiation dosimetry badges, and use radiation shields whenever possible (9).
Ceiling-suspended adjunctive portable shields for the physician interventional operators are now standard practice and designed into most invasive cardiovascular procedure rooms. Crowhurst et al. (5) clearly demonstrate that incorporating an additional ceiling-mounted shield (similar to that used by the interventional operators) for the TEE operator can decrease his or her exposure approximately 5-fold. This strategy has previously been shown to be effective in simulations (10).
Adjunctive shielding to decrease exposure of all operators is clearly effective and of critical importance. However, current shield designs do not block all scattered radiation. Thus, there is an opportunity to develop enhanced shield designs that provide maximal protection while being ergonomically user-friendly. In addition, principally for the benefit of the interventional operators, it is important to consider other radiation shielding devices such the RADPAD device (RADPAD, Lenexa, Kansas). The RADPAD is a disposable shield that is placed on the patient’s abdomen and pelvis that intercepts scattered radiation not blocked by the ceiling-mounted shield. A recent study by Vlastra et al. (11) demonstrated that routine use of the RADPAD was associated with decreased operator exposure as compared to a sham device.
Non-Shielding Exposure Reduction Strategies
Any strategy that increases distance from the x-ray source will decrease operator exposure as governed by the inverse square law. For TEE operators, this might be achieved by primarily controlling the TEE probe with one hand at the controls/handle end of the probe, the use of a longer TEE probe, or even the development of robotic remote control TEE probes. For interventionalists, this could include use of longer catheters.
In addition to advances in technology, other strategies may be employed to decrease TEE operator exposure. The TEE operator can step away from the radiation source when active TEE imaging is not needed. Clear communication between the interventional operator and the TEE operator regarding when the fluoroscopic beam is on and when TEE imaging is needed can minimize the amount of time when the TEE operator is in close proximity to the radiation source while the beam is on. Verbal, visual, and even an audio confirmation of fluoroscopy beam on could reduce the TEE operator exposure.
A strategy to decrease both operator and patient exposure is to decrease the amount of radiation delivered to the patient by using several radiation-sparing tactics. These include minimizing fluoroscopy time and cine acquisition time, modulating the fluoroscopy dose per frame, decreasing the radiation detector magnification, reducing the field size (by collimation), and decreasing the frame rate. Use of these techniques can substantially reduce the radiation exposure to the patient (and concomitantly to the operators). Current x-ray systems provide tableside controls that simplify the interventional operator’s ability to adjust system radiation output to achieve an optimal balance between radiation exposure and imaging requirements. Limiting operator reliance on fluoroscopic imaging and increasing the use of TEE guidance whenever feasible to guide specific steps in interventional procedures may also help reduce the overall fluoroscopic time and exposure. Pre-procedural planning and procedural scripting of imaging steps may be effective in this regard. For example, MitraClip (Abbott Vascular, Santa Clara, California) is a predominantly TEE-guided procedure with few steps that absolutely require fluoroscopy to guide that has benefited from procedural scripting of imaging steps and goals (12). It is important that interventional operators develop sufficient facility with TEE imaging during structural procedures, and can effectively determine when TEE alone (without fluoroscopy) could be used to guide a specific step in the procedure. Similarly, successful cardiac interventions have also been described in pregnant patients using an electroanatomic mapping system guidance without the use of any fluoroscopy to avoid injury to the fetus (13). Finally, magnetic resonance imaging-guided procedures may one day replace those presently guided by TEE and fluoroscopy (14).
In conclusion, the developing effectiveness of structural cardiac interventions will likely lead to increased utilization of these procedures and, consequently, the potential for increased occupational exposure to interventionalists, TEE operators, and other surgical personnel. The current exposure doses fall comfortably within the standard recommendations for radiation safety. However, because the long-term effects of occupational exposure are not completely understood, it is important to continue to apply strategies to achieve further reduction in radiation exposure to all affected personnel. The importance of such efforts is not limited to the structural heart team, but rather is vital for all providers involved in x-ray fluoroscopy-guided procedures.
↵∗ Editorials published in the Journal of the American College of Cardiology reflect the views of the authors and do not necessarily represent the views of JACC or the American College of Cardiology.
The authors have reported that they have no relationships relevant to the contents of this paper to disclose.
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