## 1 Introduction  
Coronary angiography (CAG) and percutaneous coronary intervention (PCI) are safe and effective surgical procedures, with an overall complication rate of only 2% [1, 2]. As PCI is a form of microsurgery, it holds distinct advantages over coronary angiography. However, owing to the growing number of cardiac catheter devices and the increasing complexity of surgical procedures, cardiologists have been subjected to increasingly high radiation doses compared with ordinary radiologists [3]. Furthermore, a clinical examination can be prolonged owing to variations in patient condition, which could lead to high radiation doses in the lenses of the operators' eyes [4]. Personal radiation protection equipment, such as lead aprons, thyroid shields and lead glasses, have become standard equipment in interventional fluoroscopy. Radiation protection accessories, such as ceiling-suspended lead shielding, table lead shielding and shielding placed on patients are also used in clinical settings. Operators often use ceiling-suspended lead acrylic shields, as there are a number of materials that must be taken in and out during cardiac catheterization, including wires, balloon catheters and stents. However, an operator may choose to remove the lead acrylic shield or avoid using certain X-ray irradiation angles during procedures that require a high level of precision, such as the insertion of a catheter through a blood vessel and patient image evaluation. This occurs most frequently when transradial artery access procedures are performed by a short operator. Several studies have been conducted on the radiation exposure of operators (doctors, radiologists and nurses) and patients in cardiac catheterization [5; 6; 7; 8]. According to [PERSON] et al., the mean radiation exposure of a physician during cardiac catheterization at the eyes, thyroid glands, chest (inside the apron) and gonads is 20 mR, 2 mR-16 mR, 50 mR and 10 mR, respectively. Furthermore, eye and thyroid exposure are significantly higher during right coronary angiography than in all other diagnostic procedures [9; 10]. To elucidate differences in radiation exposure between different types of cardiac catheterization, [PERSON] et al. compared CAG to percutaneous transluminal coronary angioplasty (PTCA) in terms of completion time and radiation dosages. They found that operator radiation exposure was approximately twice as high in PTCA than in CAG; although both of these procedures have similar cineangiographic times, fluoroscopy time is more than twice as long in the former than the latter. [PERSON] et al. compared the operator radiation exposures of CAG, single-, and double-vessel PTCA, and found that irradiation outside the lead protectors was highest in double-vessel PTCA, then single-vessel PTCA and lastly, CAG. However, no significant differences were noted between these procedures inside the lead protectors [11]. [PERSON] et al. showed that the use of lead protectors reduces the radiation exposure of workers, operators, nurses and technical staff by approximately 66%, thus highlighting the importance of accessory lead shields [12]. Air kerna (AK), that is, the kinetic energy released per unit mass when an X-ray beam is traveling through air, is a measure of skin dose in radiology. Since the severity of the deterministic effect is directly proportional to radiation dosage, this effect may be assessed either by AK or radiation dose measurements. According to the linear no-threshold model, the probabilistic effect and risk of tissue damage increase linearly with radiation exposure. Hence, the probabilistic effect can be estimated using the dose-area product (DAP) [13; 14]. The 2011 report of the International Committee on Radiological Protection (ICRP) suggested that special attention should be paid to occupational exposure in medical staff [15; 16]. The report also specifically raised concerns about the deterministic and stochastic effects of radiation in personnel working in cardiac catheterization laboratories. [PERSON] et al.