Abstract
Objective: Compared with stent-assisted coiling (SAC), the Woven EndoBridge (WEB; Terumo Neuro, Aliso Viejo, CA, USA) device has been reported to reduce procedural duration, suggesting the potential to reduce radiation exposure for both patients and operators. However, whether WEB treatment results in lower radiation exposure than SAC has not been fully investigated. This study therefore aimed to evaluate radiation exposure associated with WEB treatment versus SAC in the management of unruptured wide-neck bifurcation aneurysms (WNBAs).
Methods: We retrospectively analyzed 46 patients treated for 47 unruptured intracranial aneurysms located at the basilar artery apex, middle cerebral artery bifurcation, or anterior communicating artery at our institution between February 2023 and April 2024. Patients were categorized into 2 groups based on the treatment modality: SAC or WEB device. Radiation exposure, fluoroscopy time, procedure duration, and number of imaging procedures were compared between groups.
Results: Baseline characteristics, including age, sex, and aneurysm location, did not differ significantly between groups. However, aneurysms were significantly larger in the WEB group, with both greater median aneurysm volume (61.9 vs. 43.2 mm3, P <0.001) and maximum dome diameter (8.2 vs. 5.4 mm, P <0.001). Radiation exposure was significantly lower in the WEB group, as indicated by lower median values for both air kerma (1888 vs. 3496 mGy, P <0.001) and dose–area product (126.3 vs. 158.9 Gy·cm2, P = 0.002). The WEB group also showed significantly shorter values for both fluoroscopy time (49.1 vs. 102.3 min, P = 0.003) and procedure duration (97 vs. 146 min, P = 0.01). The number of imaging procedures and contrast medium volume did not differ significantly between groups.
Conclusion: In the endovascular treatment of unruptured WNBAs, the WEB device significantly reduces radiation exposure compared with SAC, primarily by decreasing fluoroscopy time. Given this potential to minimize radiation exposure, the WEB device may be preferable when both methods are clinically viable.
Introduction
Since the publication of the International Subarachnoid Aneurysm Trial (ISAT) study, endovascular treatment (EVT) has increasingly replaced microsurgical clipping as the preferred approach for intracranial aneurysms worldwide.1–3) In EVT, wide-neck bifurcation aneurysms (WNBAs) often require adjunctive techniques such as balloon-assisted coiling, double-catheter techniques, or stent-assisted coiling (SAC) to maintain the patency of branch arteries. The introduction of low-profile, catheter-deliverable stents has significantly increased the use of SAC.4) However, a major drawback of current EVT practices is radiation exposure, which poses risks to both patients and operators. Potential hazards include tissue reactions and stochastic effects, with skin injury being the most common complication among patients and cataracts as the most common among operators.5,6) Interest in strategies to minimize radiation exposure during neuroendovascular procedures is therefore growing.
The Woven EndoBridge (WEB; Terumo Neuro, Aliso Viejo, CA, USA) device has recently emerged as an alternative treatment for WNBAs and has been available in Japan since 2020. This method involves deploying a single WEB device within the aneurysm sac via microcatheter, achieving embolization without the need for multiple coils or adjunctive techniques. Compared to SAC, WEB treatment has been reported to reduce the procedural duration,7–9) suggesting the potential for reductions in radiation exposure for both patients and operators. However, whether WEB treatment results in lower radiation exposure than SAC has not been fully investigated. This study aimed to determine whether WEB treatment reduces radiation exposure compared to SAC in the management of unruptured WNBAs.
Materials and Methods
Patient selection
This study was approved by the medical ethics committee of the Jikei University Hospital (36-063[12162]). The need to obtain informed consent was waived due to the retrospective design. The study retrospectively reviewed all 211 intracranial aneurysms treated with EVT between February 2023, when the WEB device was 1st introduced at our institution, and April 2024.
A total of 170 cases were subsequently excluded, comprising 25 ruptured aneurysms, 14 re-treatment procedures, 125 aneurysms located at bifurcation sites other than the anterior communicating artery (Acom), middle cerebral artery (MCA), or basilar artery (BA) apex, and 6 aneurysms treated with techniques other than SAC or the WEB device. After applying these criteria, 10 aneurysms were assigned to the WEB group and 31 to the SAC group (Fig. 1).
Data acquisition
Patient data extracted from examination reports included age, sex, aneurysm location, aneurysm size, volume, air kerma and dose–area product (DAP), fluoroscopy time, procedure duration, number of imaging procedures, and contrast medium volume. The air kerma and DAP are measures of radiation dose displayed on the angiography system.
Aneurysm size and volume were objectively measured using Neurovision software (version 1.73; Cybernet Systems, Tokyo, Japan), which analyzed 3D-DSA Digital Imaging and Communications in Medicine (DICOM)data.10) Procedure duration was defined as the interval between the initial and final DSA acquisitions.
Imaging and injection protocol
All procedures were performed under general anesthesia using a biplane angiography system (Artis Q; Siemens Healthcare, Forchheim, Germany). Identical fluoroscopy and DSA settings were applied to both the SAC and WEB groups, with the radiation dose automatically adjusted by the angiography system according to patient-specific factors such as body thickness and working angles. The contrast injections for the initial and final DSA acquisitions, including arterial and venous phases in standard anteroposterior and lateral projections, as well as 3D-DSA, were performed using an automated injector. All other DSA acquisitions were performed with manual injection by the operator. The injection protocol adhered to our institutional clinical guidelines, as detailed below. Diluted 70% contrast medium (300 mg/mL, Iohexol; Fuji Pharma, Tokyo, Japan) was administered using the following rates:
- • Global 2D-DSA: A total volume of 6 mL at 4 mL/s for the MCA and Acom, and a total volume of 5 mL at 3 mL/s for the BA.
- • 3D-DSA: A total volume of 19.5 mL at 3 mL/s for the MCA and Acom, and a total volume of 16.2 mL at 2.5 mL/s for the BA.
For visualization of the stent and WEB device, high-resolution cone-beam CT (CBCT) was performed after coil embolization in the SAC and after deployment and detachment of the WEB device.
Statistical analyses
Categorical variables are expressed as frequencies and percentages and were analyzed using Fisher’s exact test. Continuous variables are reported as medians with interquartile ranges (IQRs), and comparisons between groups were performed using the nonparametric Mann–Whitney U-test. All statistical analyses were performed using EZR software (Saitama Medical Center, Jichi Medical University, Saitama, Japan), which is built on R and R Commander.11) Values of P <0.05 were considered statistically significant.
Results
Patient characteristics
Patient and aneurysm characteristics are summarized in Table 1. The SAC group included 17 women (55%) with a median age of 65 years (interquartile range 56.0–70.5 years), while the WEB group included 7 women (70%) with a median age of 56 years (IQR, 50.8–66.8 years). In the SAC group, 10 aneurysms (32%) were located in the MCA, 15 (48%) in the Acom, and 6 (20%) in the BA apex. In the WEB group, 4 aneurysms (40%) were located in the MCA, 3 (30%) in the Acom, and 3 (30%) in the BA apex. No significant differences in age, sex, or aneurysm location were evident between groups.
Table 1 Clinical and aneurysm characteristics of the SAC and WEB groups
| Characteristics |
WEB group (n = 10) |
SAC group (n = 31) |
P-value |
| Age |
56 (50.8–66.8) |
65 (56–70.5) |
0.34 |
| Sex, female |
7 (70) |
17 (55) |
0.48 |
| Aneurysm characteristics |
|
|
|
| Aneurysm volume (mm3) |
61.9 (108.3–272.9) |
43.2 (29.1–65.9) |
<0.001 |
| Maximal aneurysm size (mm) |
8.2 (6.7–9.1) |
5.4 (4.6–6.0) |
<0.001 |
| Neck size (mm) |
4.4 (4.7–6.4) |
4.3 (3.9–5.6) |
0.13 |
| Location |
|
|
0.65 |
| MCA |
4 (40) |
10 (32) |
|
| Acom |
3 (30) |
15 (48) |
|
| BA apex |
3 (30) |
6 (20) |
|
P-values <0.05 are considered significant. Unless otherwise indicated, values represent the number and percentage of aneurysms or the median and interquartile range. Acom, anterior communicating artery; BA apex, apex of the basilar artery; MCA, middle cerebral artery; SAC, stent-assisted coiling; WEB, Woven EndoBridge
Median aneurysm volume was significantly larger in the WEB group (61.9 mm3, IQR 108.3–272.9 mm3) than in the SAC group (43.2 mm3, IQR 29.1–65.9 mm3; P <0.001). Median neck size did not differ significantly between groups (SAC: 4.3 mm, IQR 3.9–5.6 mm; WEB: 4.4 mm, IQR 4.7–6.4 mm; P = 0.13), whereas maximal aneurysm size was significantly larger in the WEB group (8.2 mm, IQR 6.7–9.1 mm) than in the SAC group (5.4 mm, IQR 4.6–6.0 mm; P <0.001).
Radiation dose, fluoroscopy time, and procedure duration
A summary of air kerma, DAP, fluoroscopy time, procedure duration, number of imaging procedures, and contrast medium volume is provided in Table 2. Median air kerma was significantly lower in the WEB group (1888 mGy) than in the SAC group (3496 mGy; P <0.001). Similarly, median DAP was lower in the WEB group (126.3 Gy·cm2) than in the SAC group (158.9 Gy·cm2; P = 0.002).
Table 2 Radiation exposure, fluoroscopy time, and procedure duration in the SAC and WEB groups
| Characteristics |
WEB group (n = 10) |
SAC group (n = 31) |
P-value |
| Air kerma (mGy) |
1888 (1584–2678) |
3496 (2666–4005) |
<0.001 |
| DAP (Gy·cm2) |
126.3 (103.5–146.5) |
158.9 (129.1–189.1) |
0.003 |
| Fluoroscopy time (min) |
49.1 (35.3–76.1) |
102.3 (75.9–125.3) |
0.003 |
| Procedure duration (min) |
97 (73.5–133.2) |
146 (123.5–180.5) |
0.01 |
| Number of imaging procedures (shots) |
46 (42–58) |
54 (48–65) |
0.14 |
| Contrast medium volume (mL) |
160 (119–174) |
179 (144–201) |
0.082 |
P-values <0.05 are considered significant. Unless otherwise indicated, values represent the median and interquartile range. DAP, dose–area product; SAC, stent-assisted coiling; WEB, Woven EndoBridge
Median fluoroscopy time was significantly shorter in the WEB group (49.1 min) than in the SAC group (102.3 min; P = 0.003). Median procedure duration was also shorter in the WEB group (97 min) than in the SAC group (146 min; P = 0.01).
The median number of imaging procedures was 54 shots in the SAC group and 46 shots in the WEB group, while the median volume of contrast medium used was 179 mL in the SAC group and 160 mL in the WEB group, respectively. No significant differences between groups were seen for either parameter. Box-and-whisker plots illustrating these parameters are shown in Supplementary Fig. 1.
Representative cases: comparison of SAC and WEB treatments
Figures 2 and 3 compare radiation dose, fluoroscopy time, and procedure duration between SAC and WEB treatments in MCA and BA aneurysms of similar volume. For both aneurysm types, air kerma, fluoroscopy time, and procedure duration were more than twice as high in the SAC group as in the WEB group.
Discussion
Key findings of this study
These findings demonstrate that, with EVT for unruptured WNBAs, the radiation dose is significantly lower with WEB treatment than with SAC. Although the number of imaging procedures (including 3D-DSA and CBCT) was similar between groups, the WEB group exhibited markedly shorter overall procedure duration, in turn leading to reduced fluoroscopy time and further lowering of the radiation exposure. In contrast to SAC, which requires sequential coil packing and stent deployment, the single-step deployment of the WEB device streamlines the intervention and minimizes both procedure and fluoroscopy duration. At our institution, larger aneurysms tended to be treated with the WEB device rather than with SAC, which likely explains the significantly larger aneurysm size observed in the WEB group compared with the SAC group.
WEB treatment for WNBAs: shorter procedure duration and lower radiation exposure
In the treatment of WNBAs, WEB treatment significantly reduces both procedure and fluoroscopy time compared with SAC. In a systematic review by Ohadi et al.,7) 5 studies including 298 patients treated with SAC and 203 patients treated with WEB were analyzed; the mean difference in overall procedural duration was 38.2 min, with significantly higher values in the SAC group (95% confidence interval [CI] 26.9–49.6, I2 = 53.4%). Lubicz et al.12) reported that the WEB procedure was completed in under 20 min for 17 of the 19 patients with WNBAs, while the WEB-IT study13) reported a mean fluoroscopy time of 30.2 ± 15.7 min. Although the present study reported a mean fluoroscopy time of 49.1 min with WEB treatment —longer than in previous reports—the procedure duration was still significantly shorter than that for SAC. The longer procedure duration observed in this study, compared with previous reports, may be attributed to our institutional approach aimed at minimizing complications. Specifically, we place strong emphasis on carefully confirming stent apposition to the parent vessel in SAC procedures and accurate device positioning within the aneurysm in WEB procedures using detailed fluoroscopic and angiographic assessments. Additionally, WEB treatment is still in the early stages of adoption at our institution, and as operator proficiency improves, procedure times are expected to decrease, potentially widening the difference in procedural and fluoroscopy time between SAC and WEB.
Radiation exposure in EVT: clinical implications and risk mitigation
EVT is associated with radiation exposure, a critical concern due to its potential complications. Radiation doses of 2 Gy can cause erythema and cataracts, while 7 Gy may lead to permanent epilation and 12 Gy to delayed skin necrosis. Reports have documented temporary epilation following interventional neuroradiology procedures.14–16) A review by Perry et al. found that 52 of 1025 neurointerventional cases (5.1%) received radiation doses exceeding 5 Gy, with 5 patients experiencing temporary skin or hair damage.17) Among these, 25 cases had undergone intracranial aneurysm coil embolization. Similarly, Choi et al. reported temporary epilation in 18 of 151 patients (11.9%) who underwent EVT for intracranial aneurysms, occurring 10–30 days post-procedure.18)
Excessive radiation exposure also poses risks to operators. A review of 34 studies on occupational radiation exposure during interventional procedures identified cancer and cataracts as primary concerns.6) Karatasakis et al. evaluated lens findings using slit-lamp examination and grading in 99 individuals occupationally exposed to ionizing radiation and 18 unexposed controls. The prevalence of cortical and posterior subcapsular lens changes, including potential findings, was significantly higher in the exposed group (47%) compared to controls (17%, P = 0.015). In addition, a correlation was observed between years of work and cataract prevalence (P <0.001).19) In response to accumulating evidence on the effects of ionizing radiation, the International Commission on Radiological Protection reduced the annual equivalent dose limit for the eye lens from 150 to 20 mSv.20) Therefore, when safety and efficacy are comparable, prioritizing strategies that minimize radiation exposure is essential for optimizing both patient and operator safety.
Previous studies have demonstrated no significant differences in safety and efficacy between treatment with the WEB device and SAC for unruptured WNBAs.21–23) Given the potential to reduce radiation exposure, WEB treatment may be the preferred treatment option when both strategies are feasible. These findings should be interpreted in the context of the “as low as reasonably achievable” principle to mitigate radiation-related risks while considering social and economic factors.24)
Limitations
This study showed several limitations. First, the device size for all WEB procedures was predetermined using preoperative simulations with a 3D-printed model based on diagnostic angiographic data. This approach eliminated the need for intraoperative device resizing, whereas previous studies have reported that approximately 30% of WEB procedures require device resizing,25) potentially contributing to reduced fluoroscopy time and radiation exposure. When resizing is necessary, fluoroscopy time is naturally increased, leading to greater radiation exposure. Thus, under standardized clinical conditions, the difference in radiation doses between SAC and WEB may be smaller than observed in this study. Institutions without access to preoperative simulation may also experience less pronounced differences in radiation exposure between SAC and WEB.
Second, operator experience varied, which may have influenced procedural duration, fluoroscopy time, and radiation exposure. However, all SAC procedures were performed by board-certified neurointerventionalists or under their supervision, in accordance with standardized institutional protocols. Moreover, the operators were highly experienced with SAC, making it unlikely that operator variability significantly affected outcomes in this group. In contrast, the WEB group included the first 10 consecutive cases performed at our institution, during a period when the operators were still in the early phase of the learning curve. Consequently, procedural durations in the WEB group may have been prolonged due to limited operator proficiency. As experience with the WEB device accumulates, differences in procedural metrics between the SAC and WEB groups may become more pronounced.
Finally, this was a retrospective, single-center study conducted using a single angiography system in a relatively small cohort, limiting the generalizability of the results. Future research should validate these findings through prospective, multicenter studies with larger cohorts and multiple angiography systems. Despite these limitations, our study yielded valuable insights, demonstrating that WEB treatment significantly reduces radiation exposure compared to SAC in the EVT of unruptured WNBAs.
Conclusion
As EVT for unruptured WNBAs, WEB treatment may reduce radiation exposure compared to SAC by significantly decreasing fluoroscopy time. Given this potential to minimize radiation exposure, WEB may be the preferred treatment option when both approaches are clinically feasible.
Supplementary Information
Supplementary Fig. 1. Box-and-whisker plots of results
Box-and-whisker plots illustrate air (a) kerma, (b) DAP, (c) fluoroscopy time, (d) procedure duration, (e) number of imaging procedures, and (f) contrast medium volume. DAP, dose–area product; SAC, stent-assisted coiling; WEB, Woven EndoBridge
Disclosure Statement
The authors declare that they have no conflicts of interest.
References
- 1) Molyneux AJ, Kerr RS, Yu LM, et al. International subarachnoid aneurysm trial (ISAT) of neurosurgical clipping versus endovascular coiling in 2143 patients with ruptured intracranial aneurysms: a randomised comparison of effects on survival, dependency, seizures, rebleeding, subgroups, and aneurysm occlusion. Lancet 2005; 366: 809–817.
- 2) McDonald JS, McDonald RJ, Fan J, et al. Comparative effectiveness of ruptured cerebral aneurysm therapies: propensity score analysis of clipping versus coiling. AJNR Am J Neuroradiol 2014; 35: 164–169.
- 3) McDonald JS, McDonald RJ, Fan J, et al. Comparative effectiveness of unruptured cerebral aneurysm therapies: propensity score analysis of clipping versus coiling. Stroke 2013; 44: 988–994.
- 4) Satow T, Ikeda G, Takahashi JC, et al. Coil embolization for unruptured intracranial aneurysms at the dawn of stent era: results of the Japanese registry of neuroendovascular therapy (JR-NET) 3. Neurol Med Chir (Tokyo) 2020; 60: 55–65.
- 5) Wagner JB. Radiation protection and safety in interventional radiology. Radiol Technol 2020; 91: 431–442.
- 6) Ko S, Kang S, Ha M, et al. Health effects from occupational radiation exposure among fluoroscopy-guided interventional medical workers: a systematic review. J Vasc Interv Radiol 2018; 29: 353–366.
- 7) Ohadi MAD, Asef SA, Zamani R, et al. The Woven EndoBridge device as a good alternative treatment for stent assisted coiling in intracranial bifurcation aneurysms: a systematic review and meta-analysis. Neurosurg Rev 2024; 47: 825.
- 8) Baek J, Jeong HW, Han J-Y, et al. Assessing radiation exposure and contrast agent utilization: a comparative analysis of the Woven EndoBridge device and stent-assisted coil embolization for managing unruptured wide-neck bifurcation aneurysms. Neurointervention 2024; 19: 148–155.
- 9) Rai AT, Turner RC, Brotman RG, et al. Comparison of operating room variables, radiation exposure and implant costs for WEB versus stent assisted coiling for treatment of wide neck bifurcation aneurysms. Interv Neuroradiol 2021; 27: 465–472.
- 10) Takao H, Ishibashi T, Saguchi T, et al. Validation and initial application of a semiautomatic aneurysm measurement software: a tool for assessing volumetric packing attenuation. AJNR Am J Neuroradiol 2014; 35: 721–726.
- 11) Kanda Y. Investigation of the freely available easy-to-use software ‘EZR’ for medical statistics. Bone Marrow Transplant 2013; 48: 452–458.
- 12) Lubicz B, Mine B, Collignon L, et al. WEB device for endovascular treatment of wide-neck bifurcation aneurysms. AJNR Am J Neuroradiol 2013; 34: 1209–1214.
- 13) Fiorella D, Molyneux A, Coon A, et al. Demographic, procedural and 30-day safety results from the WEB Intra-saccular Therapy Study (WEB-IT). J Neurointerv Surg 2017; 9: 1191–1196.
- 14) Valentin J. Avoidance of radiation injuries from medical interventional procedures, ICRP Publication 85. Ann ICRP 2000; 30:7–67.
- 15) Mooney RB, McKinstry CS, Kamel HAM. Absorbed dose and deterministic effects to patients from interventional neuroradiology. Br J Radiol 2000; 73: 745–751.
- 16) Huda W, Peters KR. Radiation-induced temporary epilation after a neuroradiologically guided embolization procedure. Radiology 1994; 193: 642–644.
- 17) Perry BC, Ingraham CR, Stewart BK, et al. Monitoring and follow-up of high radiation dose cases in interventional radiology. Acad Radiol 2019; 26: 163–169.
- 18) Choi DH, Yoo CJ, Park CW, et al. Practical dose parameter values for the prediction of the adverse effect of neurointerventional radiation: relationship between the dose parameters and temporary alopecia after intracranial coil embolization. World Neurosurg 2019; 130: e222–e229.
- 19) Karatasakis A, Brilakis HS, Danek BA, et al. Radiation-associated lens changes in the cardiac catheterization laboratory: results from the IC-CATARACT (CATaracts Attributed to RAdiation in the CaTh lab) study. Catheter Cardiovasc Interv 2018; 91: 647–654.
- 20) Stewart FA, Akleyev AV, Hauer-Jensen M, et al. ICRP publication 118: ICRP Statement on tissue reactions and early and late effects of radiation in normal tissues and organs—threshold doses for tissue reactions in a radiation protection context. Ann ICRP 2012; 41: 1–322.
- 21) Zheng H, Zhao Y, Zhou H, et al. Mid-to-long term safety and efficacy of Woven EndoBridge device for treatment of intracranial wide neck aneurysms: a systematic review and meta-analysis. Clin Neurol Neurosurg 2023; 232: 107861.
- 22) Cagnazzo F, Cloft HJ, Lanzino G, et al. WEB (Woven EndoBridge) device for intracranial aneurysm treatment: technical, radiological, and clinical findings in a consecutive North American cohort. Acta Neurochir (Wien) 2023; 165: 2077–2086.
- 23) Kashkoush A, El-Abtah ME, Srivatsa S, et al. Comparative effectiveness of stent-assisted coiling and Woven EndoBridge embolization for the treatment of unruptured wide-neck bifurcation intracranial aneurysms. J Neurosurg 2023; 138: 1487–1493.
- 24) The 2007 Recommendations of the International Commission on Radiological Protection. ICRP publication 103. Ann ICRP 2007; 37: 1–332.
- 25) Pressman E, Weinberg JH, Baig AA, et al. Validity of Woven EndoBridge sizing based on the device-to-aneurysm volume ratio. Interv Neuroradiol 2024 Nov 14. 2024. doi.org/10.1177/15910199241298327. [Epub ahead of print]
