Efficacy of a Protective Sheet for Reducing Ocular Radiation Exposure During Transcatheter Aortic Valve Implantation

Abstract

Background: The use of hybrid operating rooms (HOR) for transcatheter aortic valve implantation (TAVI) has increased, so radiation exposure during procedures that use X-ray fluoroscopy is a fundamental problem not only for patients but also for surgeons and interventional cardiologists, increasing the risk of cataracts among operators. We investigated the efficacy of leaded glasses and protective sheets for ocular radiation protection.

Methods and Results: Between January 2020 and February 2021 we enrolled 54 TAVI procedures using the transfemoral approach. The subjects were divided into a curtain protection group (Group C, n=20), glass protection group (Group G, n=17), and sheet protection group (Group S, n=17). The cumulative dose (CD) of the operators showed a decreasing trend in Group S compared with the other two groups. The CD normalized by dose area product (CD/DAP) of the operators was significantly reduced in Group S compared with Group C. However, Group G showed no significant difference compared with Group C. Regarding the distribution of CD/DAP, Group S had a significantly lower distribution than that in groups C and G.

Conclusions: Protective sheets provide more stable radiation protection than conventional curtains or leaded glasses.

In recent years, transcatheter aortic valve implantation (TAVI) has become the standard treatment for patients with high-risk aortic stenosis, and the use of hybrid operating rooms (HORs) for TAVI has increased. In the HOR, radiation exposure from X-ray fluoroscopy procedures is an important risk for patients, surgeons and interventional cardiologists. In particular, ocular radiation exposure increases the risk of cataracts among operators.^1–3 Protective leaded glasses are currently used for personal protection in the HOR to reduce radiation exposure, but their efficacy is inconsistent because of the changing head position of the operator intraoperatively.⁴

Moreover, because radiation from the C-arm in the HOR irradiates from under the operating table, scatter radiation (SR) contributes to greater exposure of the operators, which cannot be prevented sufficiently by leaded glasses. Thus, a reduction in SR is important for protecting the surgeon’s eyes. Yokota et al investigated the efficacy of an intraoperative disposable radiation protective sheet in preventing radiation exposure,⁵ so in this study we investigated the efficacy of leaded glasses and protective sheets for ocular radiation protection.

Methods

This study included 54 TAVI procedures using the transfemoral approach between January 2020 and February 2021, all performed in the HOR of the Osaka University Hospital using a single angiography system (ARTIS Pheno; Siemens Healthcare, Germany). All patients gave informed consent, and the study was approved by the Ethical Review Board of Osaka University. The study was conducted according to the “Declaration of Helsinki”. The subjects were divided into a curtain protection group (Group C, n=20), glasses protection group (Group G, n=17), and sheet protection group (Group S, n=17). Group C used the preset curtain protection in the HOR, Group G used the curtain protection and leaded glasses (Eye-P Glass, Muranaka Medical Instruments Co., Ltd., Japan; containing 0.07 mm Pb), and Group S used the curtain protection and a protective sheet. To measure the cumulative dose (CD; μSv) of intraoperative exposure, a dosimeter (ED3 Active Extremity Dosimeter, John Caunt Scientific Ltd., Lancashire, UK) was used. In groups C and S, the dosimeter was attached to the left side of the surgeon’s head (Figure 1A), near the eyes but outside the leaded glasses if they were worn, to evaluate the protective efficacy of the curtain and sheet. In those groups, the decision to wear leaded glasses was left to the operators’ discretion, because wearing a surgical magnifier may be necessary. In Group G, the dosimeter was attached to the glasses to evaluate their protective efficacy (Figure 1B). In Group S, the RadPad was used (Worldwide Innovations and Technologies, Inc., Kansas City, MO, USA), which is a disposable sterile drape containing neither lead nor vinyl, and with lead equivalency of 0.25 mm at 90 kVp. There are various sizes and shapes of sheets to suit different situations, and in this study it was 37×42 cm with a 4-cm hole for the access site. As previously reported,⁵ the sheet is placed over the pelvis after femoral access site preparation and before starting the endovascular procedure (Figure 2). The dose area product (DAP; Gy/cm²) for the patient was measured using the HOR angiography system. CD normalized by DAP (CD/DAP), defined as the dose received by the surgeon (μSv) for every 1Gy/cm² irradiated to the patient, was calculated and applied in this study to isolate differences in patient radiation doses for each procedure.^5,6

Figure 1.

Dosimeter attached (A) to the left side of the head of the operator or (B) inside the protective glasses.

Figure 2.

Protective sheet.

Statistical Analysis

Statistical analyses were performed using JMP PRO 16.0.0 (SAS Institute, Inc., Cary, NC, USA). Continuous variables are expressed as mean±standard deviation, standard error, or median and interquartile range. Nominal variables are expressed as numbers and percentages. Comparisons between groups were performed using the F test and Mann-Whitney U test for continuous variables, and Fisher’s exact test for nominal variables. The Brown-Forsythe test was used to analyze the distribution of variance between each group. Differences were considered statistically significant at P<0.05.

Results

The patients’ characteristics are shown in the Table. There were no significant differences in age or body mass index among the groups, nor were there significant difference in procedural factors such as operative time, fluoroscopy time, and the amount of contrast. DAP, which indicates the patient’s radiation dose, was 51.4 Gy/cm² in Group C, 70.2 Gy/cm² in Group G, and 50.6 Gy/cm² in Group S, showing no significant difference among the groups (P=0.7581). In addition, there was no significant difference in DAP using digital angiography or digital subtraction angiography, which are high radiation dose imaging methods (P=0.4940). The CD of the operators was 235 μSv in Group C, 231 μSv in Group G, and 178 μSv in Group S, with a lower trend in Group S (P=0.1940, Figure 3). The CD/DAP of the operators was significantly reduced in Group S (Figure 4; 3.62 µSV/Gy/cm², P=0.0443) compared with Group C (5.10 µSV/Gy/cm²), and Group G had no significant difference compared with Group C (4.16 µSV/Gy/cm², P=0.2262). There was no significant difference between groups G and S (P=0.3292). Regarding the distribution of CD/DAP, Group S had a significantly lower distribution (standard deviation (SD)=0.70, P=0.0051; Figure 5) compared with Group C (SD=2.01) and Group G (SD=2.04). In Group G, which had a higher distribution, CD/DAP values were compared by each operator or simultaneous operators (Figure 6, P=0.2958). Operator 6 had a low distribution (SD=0.9757), while operators 3 and 4 each had a high distribution (SD=2.591 and 2.931, respectively).

Table. Patients’ Characteristics

	Conventional (n=20)	Protective glasses (n=17)	Protective sheet (n=17)	P value
Patients
Age (years±SD)	84.2±6.26	83.2±6.57	83.8±3.07	0.7174
Male	11 (35%)	9 (53%)	3 (18%)	<0.05
BMI (kg/m2±SD)	22.0±4.57	22.0±4.17	23.0±4.21	0.6289
Procedure
Contrast (mL±SD)	51.3±18.8	62.2±21.0	58.9±26.4	0.2223
Operative time (min±SD)	70.3±15.7	64.6±22.6	75.4±25.0	0.1856
Fluoroscopy time (min±SD)	17.4±5.41	19.2±7.12	16.9±7.66	0.3875
DAP by fluoroscopy and DA/DSA (Gy/cm2)	51.4±35.1	70.2±55.7	50.6±28.6	0.7581
DAP by DA/DSA (Gy/cm2)	18.2±17.0	24.9±33.8	15.7±13.1	0.4940

Values are mean±SD or median (interquartile range: P25–P75). BMI, body mass index; DA, digital angiography; DAP, dose area product; DSA, digital subtraction angiography; SD, standard deviation.

Figure 3.

Cumulative dose of the operator in the 3 groups of radiation protection device.

Figure 4.

CD/DAP (CD normalized by DAP) of the operator in the 3 groups of radiation protection device. CD, cumulative dose; DAP, dose area product.

Figure 5.

Distribution of CD/DAP in the 3 groups of radiation protection device. CD, cumulative dose; DAP, dose area product.

Figure 6.

Distribution of CD/DAP in Group G by operator. CD, cumulative dose; DAP, dose area product.

Discussion

The recent increase in the use of HORs may have increased the risk of cataracts in endovascular surgeons through radiation exposure from the angiography systems installed in HORs.^1–3 Guidelines from the International Commission on Radiological Protection suggest that healthcare workers’ eye exposure to radiation, especially the lens, should be maintained at <20 mSv averaged over 5 years.⁷ In Japan also, equivalent dose limits for lenses were lowered to that same limit in April 2021.⁸ Given these guidelines, the present results suggested that if only the preset protective curtains in the HOR are used, operators would be able to perform approximately 85 procedures per year.

Protective glasses with lead-containing lenses are commonly used.^9,10 In the latest Japanese guideline, their use during a fluoroscopic guided catheter intervention, including TAVI, is a Class 1 indication.⁸ Although these glasses have proven to be relatively valuable in protecting the eyes, there are reports that the protective effect is inconsistent because of the change position of the surgeon’s head during the operation, and the positioning of the operating table and C-arm.^4,11–13 Thus, glasses alone do not always provide adequate protection. In addition, Merrachi et al reported that the incidence of cataracts is exceptionally high in the left eye,¹⁴ suggesting the need for protection on the operator’s side that is closer to the C-arm.

Our results suggested that the effectiveness of glasses as protection varies according to the surgeon involved, which is consistent with previous reports suggesting that glasses alone may not be sufficient protection.^15,16 Using a protective sheet was effective regardless of the surgeon and should be considered a standard protective measure. Because leaded glasses and protective sheets differ in their form of protection, both can be used and the combination should provide additional protection. The protective sheet used in this study was a sterile disposable drape that does not contain lead and can shield 50–95% of SR.¹⁷ It is easy to install, does not interfere with the surgical field in the chest area, and does not increase the radiation dose to the patient.

Study Limitations

Primarily, the small sample size and that not all groups were double-blinded. The results of the comparison of CD/DAP in groups C and S suggested that the use of protective sheets significantly reduced the radiation dose, but the addition of leaded glasses, which are commonly used in clinical practice, would further reduce the radiation dose to the ocular lens. Consequently, it is recommended to investigate the efficacy of combination of leaded glasses and protective sheets in providing better radiation protection.

Conclusions

Protection with leaded glasses may be inadequate, with varying efficacy depending on the procedure and operator. However, protective sheets can provide durable protection regardless of the operative situation. Protection using both sheets and glasses should provide more reliable protection.

Acknowledgments

The authors thank Yasuhiro Yanagawa and Hiroshi Toda for their technical assistance in the preoperative settings. The authors gratefully acknowledge the work of past and present members of their departments.

Sources of Funding

This study did not receive any specific funding.

IRB Information

This study was approved by the Ethical Review Board of Osaka University Hospital (Approval No. 16105).

Disclosures

Y.S. is a member of Circulation Journal’s Editorial Team.

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