Body Surface Radiation Exposure in Interventional Echocardiographers During Structural Heart Disease Procedures

Background The distribution of radiation exposure on the body surface of interventional echocardiographers during structural heart disease (SHD) procedures is unclear. Objectives This study estimated and visualized radiation exposure on the body surface of interventional echocardiographers performing transesophageal echocardiography by computer simulations and real-life measurements of radiation exposure during SHD procedures. Methods A Monte Carlo simulation was performed to clarify the absorbed dose distribution of radiation on the body surface of interventional echocardiographers. The real-life radiation exposure was measured during 79 consecutive procedures (44 transcatheter edge-to-edge repairs of the mitral valve and 35 transcatheter aortic valve replacements [TAVRs]). Results The simulation demonstrated high-dose exposure areas (>20 μGy/h) in the right half of the body, especially the waist and lower body, in all fluoroscopic directions caused by scattered radiation from the bottom edge of the patient bed. High-dose exposure occurred when obtaining posterior-anterior and cusp-overlap views. The real-life exposure measurements were consistent with the simulation estimates: interventional echocardiographers were more exposed to radiation at their waist in transcatheter edge-to-edge repair than in TAVR procedures (median 0.334 μSv/mGy vs 0.053 μSv/mGy; P < 0.001) and in TAVR with self-expanding valves than in those with balloon-expandable valves (median 0.067 μSv/mGy vs 0.039 μSv/mGy; P < 0.01) when the posterior-anterior or the right anterior oblique angle fluoroscopic directions were used. Conclusions During SHD procedures, the right waist and lower body of interventional echocardiographers were exposed to high radiation doses. Exposure dose varied between different C-arm projections. Interventional echocardiographers, especially young women, should be educated regarding radiation exposure during these procedures. (The development of radiation protection shield for catheter-based treatment of structural heart disease [for echocardiologists and anesthesiologists]; UMIN000046478)

S tructural heart disease (SHD) is a new field in cardiovascular medicine.
Echocardiologists play a key role in ensuring proper patient selection and in the technical success of SHD procedures via echocardiographic monitoring and guidance. 1 However, risks of radiation exposure to echocardiologists who perform transesophageal echocardiography (TEE) in cardiac catheterization or hybrid cardiac surgical suites have been noted. 2 Protective equipment such as mobile, lead-containing, acrylic sheets, and lead curtains are typically only used by catheter operators in cardiac catheterization suites.3,4 Interventional echocardiographers are exposed to a higher radiation dose than the first catheter operator in SHD procedures. [5][6][7] More female doctors practice echocardiography than other invasive subspecialties in the U.S. and Japan. 8,9 Radiation exposure in female health care workers should not exceed 20 mSv/y over 5 years for the lens of the eye, 500 mSv/y for the skin, and 1 mSv during the pregnancy period for the embryo/ fetus. 3,4,10,11 In addition, echocardiologists who are involved in transcatheter edge-to-edge repairs (TEERs) tend to be younger than other health care workers. 9 Therefore, radiation exposure during SHD procedures is a major challenge for female echocardiologists, especially those in training or those who are beginning their careers, as these career phases often coincide with the childbearing years. 1,8 Monitoring the exposure dose as accurately as possible is extremely important to avoid radiationrelated injuries. 12 The distribution of radiation exposure on the body surface of each interventional echocardiographer is still unclear. Therefore, this study estimated and assessed the radiation exposure on the body surface of interventional echocardiographers performing TEE in a hybrid cardiac surgical suite using a Monte Carlo simulation and measuring real-life radiation exposure during SHD procedures.

METHODS
MONTE CARLO SIMULATION SYSTEM. The fast dose estimation system for interventional radiology (FDEIR) Monte Carlo system was used to estimate the exposure dose. 12 FDEIR simulates the radiation exposure dose in the diagnostic energy range using the Monte Carlo method. Previous studies have validated its accuracy using dosimeters and other Monte Carlo approaches. [12][13][14] The simulation was conducted using a single Tesla P100 graphical processing unit (NVIDIA Corp) on a supercomputing system (SGI Technol Corp), based on a previously reported method. 12 The geometry was set to obtain the calibration factor (Supplemental Figure 1). Two radio-  16 For simplicity, other tissues were treated as water or air.
The risk of radiation dermatitis during TEER of the mitral valve-where the x-ray beam used for cardiac fluoroscopy was aimed at the heart of the patient model-was determined in the simulation. These conditions were determined based on the procedure for TEER of the mitral valve at our institution using a fluoroscopic unit (Allura Xper FD20 X-ray system).
The fluoroscopic conditions are presented in Supplemental   Overall, greater radiation exposure was found at the waist than at the chest (median: 11.5 mSv vs 2.0 mSv; Table 1). The overall group had higher radiation exposure at the waist (P < 0.05) than at the chest. Differences in the radiation exposure per cumulative air kerma (CAK) in the neck, chest, and waist were observed between the overall and TEER groups (both at P < 0.001). The overall and TEER groups had   Radiation-related skin injury is one of the hazards in various interventional radiology and TAVR procedures. 18,19 Based on the simulation results, interventional echocardiographers may not reach the radiation dose limit for the skin, which is 500 mSv/y, Thus, to reduce lens exposure in this situation, appropriate protective eyewear with side protection that securely fits on the face should be used. 21 The simulation demonstrated that absorbed dose rates were higher in the PA and cusp-overlap views, especially on the right side. The TEER procedure, in which the PA view is the basic fluoroscopic view, resulted in more radiation exposure than the TAVR procedure. Although the TEER of the mitral valve is typically performed using more TEE than fluoroscopy guidance, interventional echocardiographers should be aware of radiation exposure during the procedure.
More radiation exposure at the waist was observed in the SEV group than in the BEV group. This may be because the cusp-overlap view, in which the right anterior oblique angle is used, is currently recommended for SEV implantation during the TAVR procedure. 22 A previous study reported that the right anterior oblique angle C-arm projections predominantly increase the radiation exposure dose of interventional echocardiographers. 5 Furthermore, because SEV requires a longer time to achieve full expansion than BEVs during deployment, the irradiation time was significantly longer than that of the BEV group. Therefore, interventional echocardiographers face longer exposure times and higher exposure rates at their right waist and lower body during transfemoral TAVR with a SEV.
The basic tools of occupational radiological protection are time, distance, and shielding. 16  In addition, a high-efficiency particulate air filter must be installed on the ceiling without interfering with the rails of the C-arm. Shadowless lights are also needed in the hybrid cardiac surgery suite. Hence, because of all the equipment needed on the ceiling, many institutions cannot install ceiling-suspended protective panels. 3 In addition, lead curtain rubber shields that protect against exposure from scattered radiation can often not be hung from surgical beds based on product specifications. 3 Therefore, a freestanding floor-mounted protective board should be used. Although a prototype for use during SHD procedures has been reported, 24 there are no available products that do not interfere with the TEE  Values are median (IQR). a P < 0.05 vs chest. b P < 0.01 vs chest.
monitoring and guidance equipment. Such products should be developed as soon as possible.
Radiation exposure during SHD procedures is not limited to interventional echocardiographers and catheter operators. The SHD procedure is performed under general or local anesthesia. 25 Therefore, anesthesiologists who work near the location of the echocardiologist may also be exposed, as noted in a previous study. 26