Radiography is a fundamental, economical, and commonly used modality for diagnosing a wide range of illnesses (7,9). In veterinary medicine, animals are restrained to obtain accurate radiographic images, even if radiographers should not directly hold an animal patient during radiography. When medical X-ray equipment is used, radiation exposure may occur through three major sources: primary X-ray beams, scattered X-rays, and X-ray leakage (17). Although secondary radiation can be dispersed in any direction, most of it is scattered at an angle <45° to the incident beam, and depending on the subject and distance, the exposure dose can be up to 3% of the incident radiation dose (3). Therefore, veterinarians are more likely to be exposed to occupational radiation than doctors and dentists are (3).

Radiation exposure can result in stochastic reactions, such as cancer and genetic effects, and deterministic reactions, such as skin burns, cataracts, and bone marrow suppression (10).

Medical physicists are familiar with the ALARA principle, in which radiation doses should be maintained as low as reasonably achievable (11). Three principles are used to reduce radiation exposure: increasing the distance from the source, decreasing the exposure time, and utilizing the correct shielding equipment. Radiation exposure according to X-ray distance and imaging time may differ depending on the patient's imaging region and compliance; therefore, wearing shielding equipment is the first method for reducing radiation exposure. Radiation-shielding equipment commonly used in veterinary hospitals includes aprons, thyroid shields, glasses, and gloves (8).

Typical aprons shield the chest, abdomen, gonads, and parts of the upper legs, whereas thyroid shields, gloves, and glasses protect the thyroid gland, hands, wrists, and eyes. These accessories protect several parts of the body, but the risk of radiation exposure to the upper arm, face (except the eyes), and back areas of the body remains (20). Aprons and thyroid shields are made of lead and are heavy, restricting movement. Furthermore, wearing them for long periods can result in fatigue, back pain, and spinal diseases (1,6,12,14). Nevertheless, this problem has been addressed by using lead-free aprons and thyroid shields made of bismuth and tungsten, which are lighter than lead (15). However, because wearing radiation-shielding garments while performing radiography is difficult, the rate of filming after wearing these garments remains low (8,19).

Medical doctors use radiation-shielding devices in addition to aprons and thyroid shields to reduce radiation exposure (18). Therefore, veterinary hospitals require additional shielding systems for radiation workers to reduce the number of exposed body parts.

This study aimed to evaluate the radiation-shielding range and performance of a new shielding system compared with those of a conventional radiation-shielding system and to explain the convenience of the new shielding system. We hypothesized that the new shielding system would have a wider radiation-shielding range with a similar shielding ability and that when both systems were used together, the radiation-shielding ability would increase when only one system was used.

Study design

This study investigated the use of a new radiation-shielding system for X-ray radiation protection. The new radiation-shielding system was compared with a conventional shielding system to demonstrate whether it provides better radiation protection over a wide range. The radiation dose measurements for each protective shielding system were compared with those of the control group.

Materials

This study utilized a full-body mannequin and a cylindrical acrylic water phantom (P/N 46-241709G1; GE Healthcafé, Madison, WI, US), 23 cm in diameter and 14 cm in height, filled with distilled water, to simulate a restrained animal patient.

We used a lead-free apron, thyroid shield, glass, gloves, radiation-shield curtain, and head-shield plate for the radiation-shielding system (Fig. 1). A 0.25-mm lead equivalent lead-free apron (Rad-Ban BF2; Drview, Seoul, Korea), a 0.5-mm lead equivalent at the collar and a 0.25-mm lead equivalent upper chest region thyroid shield (Rad-Ban TH; Drview), and 0.13-mm lead equivalent glasses (XR-700, Toray, Tokyo, Japan) were used as conventional radiation-shielding systems. The new radiation-shielding system consists of a radiation-shield curtain and a head-shield plate (Fig. 2). The curtain frame, made of steel, measured 68 cm wide, 60-80 cm long, and 50-60 cm high, and had a five-layered drape made of bismuth across the frame. The shield plate consisted of a 40-cm-wide and 20-cm-long lead acrylic plate across the frame. The frame, drape, and shield plates are detachable. The drape and lead acrylic plates contained a lead equivalent of 0.25 mm. The angle of the shielding plate can be adjusted according to the convenience of the compensator. A pair of 0.25-mm lead equivalent gloves (Raon PGL02; S&C Company, Seoul, Korea) was used in both shielding systems.

Figure 1. Conventional radiation-shielding system: (A) lead-free aprons (Rad-Ban BF2; Drview), (B) thyroid shield (Rad-Ban TH; Drview), (C) glasses (XR-700; Toray, Tokyo, Japan), and (D) gloves (Raon PGL02; S&C Company) were used in both the conventional and new shielding systems. (E) Complete conventional radiation-shielding system when worn.

Figure 2. New radiation-shielding system. (A-C) Radiation-shielding curtain. (A) The curtain frame to which the curtains are attached is made of a steel frame (length, 68 cm; width, 60-80 cm; height, 50-60 cm). (B) The curtain drape is made of a five-layer bismuth material with a lead equivalent of 0.25 mm. (C) Curtain holder with curtain drapes on the X-ray table. (D-F) Head-shielding plate. (D) The head-shielding plate has a 40 × 20-cm lead acrylic plate and a lead equivalent of 0.25 mm, which can be used in the shield curtain. (E) The angle can be adjusted according to the height and convenience of the restrainer. (F) Protecting scatter radiation (red lines) from primary radiation (blue lines).

Thermoluminescent dosimeters (TLDs) (UD-802AS, Panasonic Co., Japan) were used to measure the cumulative exposure dose for each group. The TLDs were fixed at nine locations on the body: the forehead, chin, thyroid gland, left breast, right and left upper arms, gonad, and right and left upper thighs. The forehead TLD was positioned near the glasses without blocking the field of vision of the mannequin (Fig. 3).

Figure 3. (A) Thermoluminescent dosimeters (TLDs) attached on nine locations of body parts: forehead, chin, thyroid gland, left breast, right and left upper arms, gonad, and right and left upper thighs. (B) In groups using the conventional shielding system, the TLDs for the thyroid, left chest, gonad, and bilateral thigh sites are attached under the apron and thyroid shield (dashed square). Lt., left; Rt., right.

Procedures

There were three experimental groups and one control group. Group 1 wore the new radiation-shielding system with gloves. Group 2 wore both the new radiation-shielding system and the conventional shielding system with gloves. Group 3 wore the conventional shielding system with gloves. Group 4, which served as the control group, did not wear any shielding systems (Table 1, Fig. 4). The settings for the primary radiation were a tube voltage of 70 kV, a tube current of 200 mA (similar to the standard for abdominal radiography), and an exposure time of 500 ms (approximately 20 times longer than the standard exposure time) to ensure that they were as similar as possible to the set tube voltage and current. All groups underwent radiography 10 times under the same conditions. We estimated the shielding ratio of each shielding system using the dose measured at each group’s anatomical site, using the equation below (16). Group 4 was the control group, and groups 1, 2, and 3 were the experimental groups.

Table 1 . Ancillary protection equipment usage by group.

	Shield curtain (with lead plate)	Apron	Thyroid shield	Glass	Gloves
Group 1	O	X	X	X	O
Group 2	O	O	O	O	O
Group 3	X	O	O	O	O
Group 4	X	X	X	X	X

O, with ancillary protection equipment; X, without ancillary protection equipment..

Figure 4. Radiation-shielding system of each group. (A, B) Group 1: new radiation-shielding system with lead gloves. (C, D) Group 2: conventional and new radiation-shielding systems with lead gloves. (E, F) Group 3: conventional radiation-shielding system with lead gloves. (G, H) Group 4 (control group): no radiation-shielding system.

Statistical analysis

Statistical analyses were performed using SPSS for Windows (version 21.0; IBM Corp., Armonk, NY, USA) and Prism version 9.0 (GraphPad Software, San Diego, CA, USA). Data for each anatomical location are expressed as the mean ± standard deviation. For all tests, statistical significance was set at p < 0.05. Data were analyzed using the Kruskal-Wallis test after evaluating normality using the Shapiro–Wilk test. The Bonferroni test was performed for post-hoc analysis.

For each group, ten radiation exposure experiments were performed under the same conditions at all nine anatomical locations. The experimental dose study involved 1080 exposures, resulting in 108 dose readings, and measurements were calculated. After the data were evaluated, the radiation exposure doses in particular anatomical regions varied according to the use of the new radiation-shielding system.

Radiation exposure doses were measured in all experimental and control groups. In group 4 (the control group), the mean radiation exposure dose in the nine locations was 0.686 ± 0.389 mSv (Table 2). Compared to the doses associated with other anatomical regions, the exposure dose was 0.053 ± 0.015 mSv at the left thigh and 0.120 ± 0.095 mSv at the right thigh, which were approximately 7-10 times lower than those of upper body parts on average. The exposure doses in the experimental group were significantly higher than those in the control group, except for the left thigh. The radiation exposure doses for the forehead, chin, and bilateral upper arms using the new radiation-shielding system and those using both the conventional and new shielding systems were remarkably lower than those using the conventional system. The bilateral thigh exposure doses were higher when using the new radiation-shielding system than when using the conventional shielding system. The exposure dose in the thyroid, left chest, and gonad from 0.01 to 0.02 mSv did not differ significantly when using the conventional system, the new shielding system, and when using them together (Figs. 5, 6).

Table 2 . Mean radiation exposure dose (mSv) of the nine anatomical locations in the different shielding system groups.

	Group 1	Group 2	Group 3	Group 4
Forehead	0.017 ± 0.012	0.017 ± 0.012	0.433 ± 0.102	0.487 ± 0.072
Chin	0.053 ± 0.058	0.010	1.093 ± 0.190	1.197 ± 0.150
Thyroid	0.013 ± 0.006	0.010	0.010	0.857 ± 0.261
Left chest	0.010	0.010	0.013 ± 0.006	0.853 ± 0.275
Left upper arm	0.013 ± 0.006	0.010	0.693 ± 0.116	0.793 ± 0.090
Right upper arm	0.017 ± 0.012	0.010	0.603 ± 0.169	0.777 ± 0.070
Gonad	0.013 ± 0.006	0.013 ± 0.006	0.013 ± 0.006	0.997 ± 0.254
Left thigh	0.043 ± 0.015	0.013 ± 0.006	0.010	0.057 ± 0.015
Right thigh	0.063 ± 0.023	0.017 ± 0.012	0.010	0.160 ± 0.026

Figure 5. Column bar box of radiation exposure dose for each anatomical location using different radiation-shielding systems. (A) Group 1 used the new radiation-shielding system. (B) Group 2 used both a conventional and the new radiation-shielding systems. (C) Group 3 used a conventional radiation-shielding system. (D) Group 4 (control) did not use any radiation-shielding systems. Boxes: mean; error bars: standard deviation. Exposure doses measured in the control group were higher than those measured at the same anatomical locations in all experimental groups. Exposure doses were significantly higher in group 3 for the head, chin, and bilateral upper arm regions than those in groups 1 and 2. Lt., left; Rt., right.

Figure 6. Column bar box of radiation exposure dose for each group using different radiation-shielding systems. Radiation exposure dose of nine anatomical locations. (A) forehead, (B) chin, (C) thyroid, (D) Lt. chest, (E) Lt. upper arm, (F) Rt. upper arm, (G) gonad, (H) Lt. thigh and (I) Rt. thigh. Group 1 used the new radiation-shielding system. Group 1 used the new radiation-shielding system. Group 2 used both a conventional and the new radiation-shielding systems. Group 3 used a conventional radiation-shielding system. Group 4 (control) did not use any radiation-shielding systems. Boxes: mean; error bars: standard deviation. Significant reduction in exposure was observed when the new shielding systems were used in the forehead, chin, and bilateral arm regions, and no significant difference was observed in other locations (groups 1 and 2 vs. group 3). Significant differences in exposure dose were observed when conventional and the novel shielding systems were used on the bilateral thighs, respectively (group 1 vs. group 3). *p ≤ 0.05; **p ≤ 0.01; ***p ≤ 0.001; ****p ≤ 0.0001; ns, no significance; Lt, left; Rt, right.

The radiation exposure doses of groups 1, 2, and 3, which are the experimental groups, at all anatomical locations were 0.029 ± 0.028, 0.013 ± 0.009, and 0.320 ± 0.397 mSv, respectively. The exposure dose was significantly higher in group 3 than in groups 1 and 2 (p < 0.01) (Fig. 7).

Figure 7. Column bar box of mean radiation exposure values for all anatomical locations using different radiation-shielding systems. Group 1 used the new radiation-shielding system. Group 2 used both a conventional and the new radiation-shielding systems. Group 3 used a conventional radiation-shielding systems. Group 4 (control) did not use any radiation-shielding systems. Boxes: mean; error bars: standard deviation. Significant differences in exposure doses were observed among all groups except groups 1 and 2. p < 0.05 was considered significant. **p ≤ 0.01; ***p ≤ 0.001; ****p ≤ 0.0001; ns, no significance.

Because the exposures at the thyroid, left chest, gonads, and bilateral thighs were similarly low among the experimental groups, the results were excluded, and the exposure doses at the forehead, chin, and bilateral upper arms were compared again. The exposure doses of groups 1, 2, 3, and 4 were 0.025 ± 0.031, 0.012 ± 0.006, 0.706 ± 0.283, and 0.793 ± 0.296 mSv, respectively (Fig. 8). In the absence of the new radiation-shielding system, the exposure dose was significantly higher (p < 0.001).

Figure 8. Column bar box of mean radiation exposure values for the forehead, chin, and bilateral upper arm areas using different radiation-shielding systems. Group 1 used the new radiation-shielding system. Group 2 used both conventional and the new radiation-shielding systems. Group 3 used a conventional radiation-shielding system. Group 4 (the control) did not use any radiation-shielding systems. Boxes: mean; error bars: standard deviation. The exposure dose of group 3 was similar to that of group 4. p < 0.05 was considered significant. ****p ≤ 0.0001; ns, no significance.

The shielding ratio of group 2 at the anatomical positions, except for both thighs, was the same or greater than that of groups 1 and 3, and the shielding ratio at positions deemed to have been shielded was observed to be approximately 93% to 99% in the experimental groups (Table 3). The exposure rate of the left thigh was higher than that of the right thigh in all groups.

Table 3 . Shielding ratio (%) of the scattered dose after shielding in different systems.

	Group 1	Group 2	Group 3
Forehead	96.40	96.75	11.67
Chin	95.31	99.16	8.80
Thyroid	98.21	98.76	98.76
Left chest	98.73	98.73	98.44
Left upper arm	98.34	98.73	12.87
Right upper arm	97.84	98.71	22.92
Gonad	98.70	98.70	98.70
Left thigh	24.21	75.79	81.35
Right thigh	60.71	88.50	93.62

All imaging modalities have been utilized and studied in veterinary medicine; however, X-rays are the most popular for administrative, managerial, and financial reasons (9). In medicine, various suspended radiation protection systems have been studied and used to minimize exposure to various parts of the human body during computed tomography and interventional radiology (18). Although the exposure dose of X-rays is lower than that of fluoroscopy or computed tomography, the radiography number cannot be disregarded because veterinary hospitals have the largest prevalence and the use of X-rays increases yearly (5). Many different types of radiation protection systems are available worldwide. However, to our knowledge, this is the first veterinary medicine invention that uses an X-ray table with a curtain-type radiation-shielding system. Our study shows that this novel radiation-shielding system is a practical alternative to aprons, thyroid shields, and glasses for radiation protection. Additionally, the inconvenience of wearing glasses whenever performing radiography could be reduced owing to a new shielding system that was set up on the X-ray table, and the moisture issues that occurred when wearing glasses were partially resolved.

In the present study, the mean exposure doses to the left chest were the highest among the nine anatomical locations, followed by the gonads and chin. However, in a previous study, the thyroid had a higher radiation exposure than that of the chest and gonads (13), and we believe that this is because of the different phantoms used for the X-rays and the position of the restrainer. The radiation exposure dose to the upper body is 7-10 times higher than that to the bilateral thighs. It is assumed that the scattered radiation coming from the table could make its way to the restrainer’s gonads (2), and there is also the possibility that the table acted as radiation protection.

Both radiation-shielding systems showed high defense capabilities in the left chest, thyroid, and gonad positions. However, when comparing the radiation exposure in the forehead, chin, left arm, and right arm areas, high doses were measured in the conventional shielding group, similar to those in the control group, whereas those using the new shielding tool were measured as low as the left chest, thyroid, and gonad values measured in the same group. These data confirm that the novel shielding system protected a wider scan range against scattered radiation than the range protected by the classical shielding system, including the forehead, chin, and bilateral arms.

When using only the conventional shielding system, the average exposure dose to the forehead, chin, and bilateral upper arms was 0.706 ± 0.283 mSv, and it was calculated as 0.056 ± 0.023 mSv when converted according to the general abdominal radiographic criteria (70 kV, 8 mAs). According to the International Commission on Radiological Protection (ICRP), the annual equivalent dosage for radiation-related personnel is 500 mSv or less for the skin and 150 mSv or less for lenses (4). Based on the current experimental results and ICRP regulations, if 173.6 radiographs are obtained per week arithmetically, the annual skin equivalent dose will be exceeded, and if 52 radiographs are obtained per week arithmetically, the annual lens equivalent dose will be exceeded. Therefore, a new shielding system is needed to ensure the safety of the restrainer in veterinary hospitals.

Finally, a new shielding system in the form of curtains and lead plates was developed. Because the curtain drape is easy to move and both the drape and plate are detachable, correct radiation shielding cannot be achieved.

Inexperienced users may not be able to use it properly, resulting in errors such as excessive gaps in the curtain drapes or use without drapes or lead plates. Therefore, the proper application of this new radiation system must be understood.

In a previous study on the radiation-shielding rate with an apron, the shielding rate for a 0.25-mm lead equivalent apron was 88.82-90.91%; in this study, the shielding rate was 97-98%, which was higher than those reported in previous studies. This is thought to represent the difference between the primary radiation energy and the distance between the scattered radiation and dosimeter.

This study had some limitations. A cylindrical phantom was used in the experiment. Because the direction of scattered radiation caused by the cylindrical phantom may differ from the direction of scattering in an actual patient, it is believed that using the dog phantom can produce more accurate results and that the new shielding system can shield a wider range of radiation than that shielded by the conventional shielding system. However, it is impossible to shield the lower arm area, including the hand. Therefore, wearing gloves during filming is essential.

In conclusion, in this study, a new radiation-shielding system exhibited the same shielding capability as that of a conventional radiation-shielding system, can provide a wider range of radiation shields, and can solve the difficulties of using traditional shielding tools. In addition to the conventional shielding system, we anticipated that the new shielding system will be a new shielding paradigm that will further improve the safety of radiation workers in veterinary hospitals.

This work was supported by Institute for Information & communications Technology Promotion (IITP) grant funded by the Korea government (MSIP) (No. 2021-0-00490, Development of Precision Analysis and Imaging Technology for Biological Radio Waves).

The authors have no conflicting interests.