measurement of patient lens exposure during cerebral

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DOI: 10.5797/jnet.oa.2018-0068

Measurement of Patient Lens Exposure during Cerebral Endovascular Treatment Using a Scintillation Optical Fiber Dosimeter

Keisuke Kikuchi,1 Kazuma Matsumoto,1 Toshiya Nasada,1 Yoshiaki Hagihara,1 Youko Ikeuchi,1 Takafumi Iizuka,1 Chiemi Mitsuie,1 Hiromi Kishida,1 Ryousuke Fujii,1 Shinya Nakano,1 Noriko Kotoura,1 Kazutaka Uchida,2 Manabu Shirakawa,2 and Shinichi Yoshimura2

Purpose: It is difficult to predict lens radiation dose of the patients during neuroendovascular treatment due to various factors potentially affecting radiation dose such as a various working projection for individual procedures. The purpose of this study was to examine the association between the patient lens entrance dose (lens dose) during cerebral endovascular treatment and displayed dose on a system, as well as the influence of 3D imaging on lens exposure, and clarify factors influencing lens exposure.Methods: In patients who underwent cerebral endovascular treatment under general anesthesia between February and December 2017, the lens dose was measured using a real-time scintillation optical fiber dosimeter. The correlation between the lens dose and displayed dose on each system was analyzed. Furthermore, dose data were divided into fluoroscopy, DSA, and 3D imaging, and respective values as a percentage of the lens dose were calculated.Results: There was a strong correlation between the lens dose and Kerma Area Product (KAP) value. The lens dose was weakly correlated with the Air Kerma (AK) value and duration of fluoroscopy. 3D imaging for the visualization of a stent increased the value of 3D imaging as a percentage of the lens dose, and the lens dose increased with the frequency of imaging. In patients with a large field of irradiation after the establishment of a working angle, the lens dose increased.Conclusion: We evaluated the characteristics of the lens dose. In the future, the management of the lens dose should be examined.

Keywords▶ �lens dose, cone-beam computed tomography, computed tomography-like image, scintillator with optical fiber

Introduction

As endovascular treatment is minimally invasive in com-parison with surgery, it is currently applied in various fields.

Johnston et al.1) reported that endovascular treatment for cerebral aneurysms was a low-risk treatment in comparison with surgery. Endovascular treatment plays an important role in the treatment of cerebral aneurysms.

However, radiodiagnostic devices are used during endovascular treatment, and there is a risk of radiation exposure. Many studies reported radiation-related dermal disorder following endovascular treatment.2–5)

In April 2012, it was recommended in the International Commission on Radiological Protection (ICRP) Publi-cation 118 that the threshold of absorbed dose for cataract should be 500 mGy per session.6) For cerebral endovascu-lar treatment, imaging at a working angle is necessary, and the angle differs among individual patients. Therefore, it is difficult to predict the patient lens entrance dose. Several studies measured patient entrance dermal or lens doses during cerebral endovascular treatment.7–12) However, in these studies, fluorescence glass dosimeters, thermolumi-nescence dosimeters, or Gafchromic films (Ashland Inc.,

1Department of Radiological Technology, Hyogo College of Medicine, Nishinomiya, Hyogo, Japan2Department of Neurosurgery, Hyogo College of Medicine, Nishinomiya, Hyogo, Japan

Received: April 23, 2018; Accepted: July 3, 2018Corresponding author: Keisuke Kikuchi. Department of Radiolog-ical Technology Hyogo College of Medicine, 1-1 Mukogawa-cho, Nishinomiya, Hyogo 663-8501, JapanEmail: [email protected]*The abstract of this study was presented at the 33rd Annual Meeting of The Japanese Society for Neuroendovascular Therapy (2017, Tokyo).

This work is licensed under a Creative Commons Attribution-NonCommercial- NoDerivatives International License.

©2019 The Japanese Society for Neuroendovascular Therapy

Journal of Neuroendovascular Therapy Vol. 13, No. 1 (2019)

Journal of Neuroendovascular Therapy 2019; 13: 1–8

Online August 16, 2018

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Covington, KY, USA) were used for measurement. The cumulative dose in the procedure alone was measured. Therefore, it is unclear which intraoperative procedure increases the lens dose.

Dosimeters that facilitate real-time intraoperative dose monitoring include a metal oxide semiconductor field effect transistor (MOSFET) dosimeter and scintillation optical fiber dosimeter (scintillator with optical fiber [SOF]).

Safari et al.13) measured the real-time lens dose using a MOSFET dosimeter for endovascular diagnosis/treatment of the head area. However, concerning the dose measured, the characteristics of the dosimeter were not considered, and the value may have been markedly influenced by the directional dependency of the MOSFET dosimeter.14) Fur-thermore, the influence of 3D imaging was not reviewed. 3D imaging plays an important role in cerebral endovascu-lar treatment. 3D-DSA facilitates the 3D visualization of blood vessels alone; it is also useful for determining a work-ing angle. In cases of coil embolization using stent-assisted techniques or flow diverter insertion, it is possible to con-firm the position of stent fracture or insertion by obtaining CT-like images (CTLIs). However, CTLIs require a higher dose in comparison with fluoroscopy or DSA, and an X-ray tube is rotated around the head for imaging; therefore, the lens dose may increase.

The purpose of this study was to measure the lens dose during cerebral endovascular treatment, investigate its association with the displayed dose on each system and the influence of 3D imaging on lens exposure, and clarify fac-tors influencing lens exposure.

SubjectsOf patients who underwent cerebral endovascular treat-ment under general anesthesia at the Hyogo College of Medicine Hospital between February and December 2017, the entrance lens dose was measured in 29 from whom informed consent was obtained (3 males, mean age: 66 ± 13.5 years, 26 females, mean age: 66 ± 13.2 years). The subjects consisted of 25 with aneurysms (internal carotid artery: 18 patients, anterior communicating artery: 5, middle

cerebral artery: 1, and vertebral artery: 1), 3 with carotid- cavernous fistulas (CCFs) (external carotid artery: 3), and 1 with arteriovenous malformation (AVM) (superior cere-bellar artery: 1). The protocol of this study was approved by the Ethics Review Board of our hospital (Ethics Applica-tion No. 2611). The cerebral endovascular treatment proce-dures were performed using Artis Zee biplane (Siemens Healthcare, Erlangen, Germany) and Artis Zeego (Siemens Healthcare) that were angiography systems. The two sys-tems had similar flat panel detectors (FPDs) and X-ray tubes. Various conditions are presented in Table 1.

As an SOF, a MIDSOF (AcroBio Corporation, Tokyo, Japan) was used. This device has a hemispherical scintilla-tor, as a detector, at the tip of a plastic optical fiber, and the dose/dose ratio per second are expressed. When X-ray per-meates through a scintillator, optical pulse is generated and transmitted by optical fiber. It is amplified/detected in a photomultiplier tube, and the radiation dose is calculated based on discrete values.

Methods

Basic characteristics of an SOFThe basic characteristics of an SOF were investigated, as described below.

Dose dependency: The probe of an SOF was placed at the isocenter, and the fluoroscopy time was changed to 60 seconds at 10-second intervals. The cumulative radia-tion dose of the SOF was serially examined. Measurement was conducted three times, and the mean value was adopted as a representative value. Concerning imaging conditions, the tube voltage, tube current, and pulse width were estab-lished as 81.8 kV, 130.7 mA, and 12.8 ms, respectively.

Energy dependency: The probe of an SOF was placed at the isocenter, and the tube voltage was changed from 50 to 120 kV at 10-kV intervals. Irradiation was performed for 1 minute at each tube voltage. Measurement was conducted three times, and the mean value was adopted as a representa-tive value. A similar experiment was carried out using an ion-ization chamber (Radcal 9015, Toyo Medic, Tokyo, Japan),

Table 1 Parameters of X-ray equipment

Cu Filter (Fluoro/DSA) 0.6 mm/0.3 mmGrid ratio/density (/cm) 15 : 1/80Tube voltage (kV) 70–125 (automatic exposure control)Fluoroscopic pulse rate (p/sec) 7.5frame rate of DSA (frame/sec) 2, 4, 7.5Field of view (cm) 11 × 11, 16 × 16, 22 × 22, 32 × 32, 42 × 42, 42 × 48 SID (cm) 90–120

SID: source-to-image receptor distance


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Patient Lens Exposure during Cerebral Endovascular Treatment

after cerebral endovascular treatment. When a stent was used, CTLIs were additionally taken if necessary. To inves-tigate the influence of 3D imaging, the lens dose was compared by dividing the subjects into three groups: a group in which 3D-DSA alone was performed (3D-DSA group); a group in which CTLIs were additionally taken once (1CTLI group); and a group in which CTLIs were additionally taken twice (2CTLI group). Furthermore, the lens dose per session of 3D-DSA or CT-like (CTL) imag-ing was calculated. Concerning 3D-DSA conditions, the tube voltage, FPD entrance dose, frame rate, imaging time, and rotation angle were established as 70 kV, 0.36 µGy/frame, 1.50°/frame, 6 seconds, and 200°, respectively. Con-cerning CTL imaging conditions, the tube voltage, FPD entrance dose, frame rate, imaging time, and rotation angle were established as 70 kV, 1.20 µGy/frame, 0.40°/frame, 20 seconds, and 200°, respectively. On both procedures, the tube current/voltage changed through the automatic expo-sure control.

Statistical analysisTo analyze the dose of an SOF and correlations between the actual value and KAP/AK/FT, Pearson’s correlation analysis was conducted. To compare the mean values between two groups, the Mann–Whitney U-test was used. A P value of 0.05 was regarded as significant. For all statistical analyses,

and the relative dose ratio of the SOF as a percentage of the value measured using the dosimeter was calculated.

Directional dependency: The probe of an SOF was placed at the isocenter, and the C-arm angle was changed by 90° in the axial direction and by 60° in the cranial-caudal direction. Measurement was conducted three times, and the mean value was adopted as a representative value. The relative dose ratio of each angle as a percentage of the value measured at a C-arm angle of 0° was calculated. Concern-ing imaging conditions, the tube voltage, tube current, and fluoroscopy time were established as 69 kV, 6.7 mA, and 60 seconds, respectively.

Measurement of the patient lens doseWhen measuring the lens dose, the subjects were instructed to wear an eye mask so that their eyes might not be dam-aged. Kawauchi et al.15) reported that left lens exposure on diagnostic cerebral angiography was significantly higher than right lens exposure. Furthermore, Safari et al.13) placed a MOSFET dosimeter on the eyelid from the lateral side of the left eye for lens dose monitoring. This was because a lateral X-ray tube had been installed on the left side of the patient. In our hospital, a lateral X-ray tube was also installed on the left side of the patient, and the lens dose of the left eye was measured. The probe of a dosime-ter was placed from the foot side to the head side, as shown in Fig. 1.

In addition to the SOF dose data, the kerma area prod-uct (KAP), air kerma (AK), total fluoroscopic time (FT), and range of working angle in patients with aneurysms or AVM/CCF were recorded. In the aneurysm patients, the correlations between the actual value and AK/KAP/FT were analyzed with respect to frontal/lateral X-ray tubes.

To examine the influence of the field of irradiation, the lens dose was compared by dividing the subjects into four groups: a group in which the fields of irradiation for both frontal and lateral X-ray tubes after establishing a working angle in each patient were the smallest (11 cm) (FLsmall group, n = 13); a group in which the field of irradiation for a frontal X-ray tube was 11 cm (Fsmall group, n = 7); a group in which the field of irradiation for a lateral X-ray tube was 11 cm (Lsmall group, n = 3); and a group consist-ing of the other patients (wide group, n = 6).

Based on the actual values obtained and Radiation Dose Structured Report, the dose ratios of fluoroscopy, DSA, and 3D imaging as a percentage of the lens dose were cal-culated. In this study, 3D-DSA was performed before and

Fig. 1 A pocket was prepared on an eye mask (dotted line), and a probe was inserted. Immediately above the patient’s left eye, the pocket was used as a probe detector, and the lens dose was measured. The eye mask was fixed to a headrest so that it could be detached if necessary.


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we used EZR (version 1.32; Saitama Medical Center, Jichi Medical University, Saitama, Japan) on R commander software (http://www.rcommander.com/index.php).

Results

Basic characteristics of an SOFThe dose showed linearity with changes in the irradiation time. There was a strong correlation, with a correlation coefficient (r) of 0.9999 (Fig. 2a).

Concerning energy dependency, the relative dose ratio at a tube voltage of 60–80 kV was ≤5% of that of an ion-ization chamber, but that at a tube voltage of 90–120 kV was underestimated by approximately 23% at maximum (Fig. 2b).

With respect to directional dependency, the relative dose ratio when the axial direction was changed was ≤3%. When the cranial-caudal direction was changed, it showed a greater error at a deeper angle. At a caudal angle of 60°, the relative dose ratio was overestimated by approximately 8%. At a caudal angle of 45° to a cranial angle of 60°, the error was ≤5% (Fig. 2c and 2d).

Patient lens doseThe KAP, AK, FT, lens dose, and range of working angle in patients with aneurysms or AVM/CCF in this study are shown in Table 2. In the latter, the KAP, AK, and FT were significantly higher than in the former.

Figure 3 shows the correlations between the FT/AK/KAP and lens dose in those with aneurysms. The FT and

AK values for frontal/lateral X-ray tubes were weakly cor-related with the lens dose. The KAP for a frontal X-ray tube was moderately correlated with the lens dose. That for a lateral X-ray tube was strongly correlated.

The comparison of the field of irradiation with the lens dose is shown in Fig. 4. The mean lens doses in the FLs-mall, Fsmall, Lsmall, and wide groups were 77.0 ± 47.9, 67.6 ± 42.0, 57.1 ± 23.9, and 124.2 ± 90.7 mGy, respec-tively. In the wide group, the value was higher, but there were no significant differences among the four groups.

The mean lens dose with respect to the frequency of CTL imaging is shown in Fig. 5. In the 1CTLI group, the FT was significantly shorter than in the 3D-DSA group. CTL imaging increased the ratio of 3D imaging as a per-centage of the lens dose threefold. There were no differ-ences in the lens dose between the 1CTLI/2CTLI and 3D-DSA groups. In the 2CTLI group, the lens dose was significantly higher than in the 1CTLI group.

The mean AK displayed on the system per session of 3D-DSA was 74.3 ± 12.9 mGy, and the mean lens dose was 8.0 ± 2.8 mGy. That per session of CTL imaging was 283.2 ± 47.9 mGy, and the mean lens dose was 33.4 ± 10.1 mGy. On CTL imaging, the AK displayed on the system and lens dose were significantly higher than on 3D-DSA (P <0.001).

Discussion

When conducting dosimetry of a procedure requiring imaging at various working angles, such as cerebral endo-vascular treatment, the setting of a dosimeter is important.

Fig. 2 Characteristics of a scintillation optical fiber dosimeter. (a) Dose dependency, (b) energy dependency, (c) directional dependency in the axial direction, and (d) directional depen-dency in the longitudinal direction.


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Table 2 Exposure parameters, left lens dose (LL dose) and range of working angle

Aneurysm AVM • CCF P value

KAP (Gy cm2) 129.6 ± 51.2* 264.9 ± 123.0* 0.013(61.6–282.6) (131.0–427.8)

AK at IRP (mGy) 2450.0 ± 1397.8* 4962.0 ± 2502.8* 0.030 (874.4–7126.0) (2294.0–7358.0)

FT (min) 66.8 ± 39.6* 198.0 ± 145.3* 0.036(19.1–173.9) (44.9–393.2)

LL Dose (mGy) 78.0 ± 61.2* 97.2 ± 38.9* 0.253(18.2–296.2) (59.0–148.4)

Working angle LAO99°–RAO46° LAO0°–RAO56° —(Frontal) CRA45°–CAU38° CRA27°–CAU33°Working angle RAO41°–RAO128° RAO90°–RAO99° —(Lateral) CRA46°–CAU25° CRA8°–CRA0°*mean ± standard deviation. AK: air kerma; AVM: arteriovenous malformation; CAU: caudal; CCF: carotid-cavernous fistula; CRA: cranial; FT: fluoroscopic time; IRP: interventional reference point; KAP: kerma area product; LAO: left anterior oblique; LL: left lens; RAO: right anterior oblique

Fig. 3 Correlations between the FT (a) AK, (b) KAP, and (c) patient lens dose. AK: air kerma; FT: fluoroscopic time; KAP: kerma area product

Fig. 4 Comparison of the lens dose among different fields of irradiation.


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AK, and FT were significantly higher in the former. In aneurysm treatment, much information is obtained by increasing the magnification rate for the field of irradia-tion on coil rolling or stent insertion. However, for CCF treatment, it is necessary to differentiate blood vessels to be embolized from those to be preserved, increasing the frequency of DSA. In addition, excessively magnified imag-ing may eliminate normal blood vessels from the field of view. For this reason, CCF treatment may have required a longer operative time and a greater field of irradiation com-pared with aneurysm treatment. Furthermore, the external carotid artery was primarily treated in all CCF patients; there was a specific distance between the field of irradia-tion and lens, and this may have contributed to a gradual increase in the lens dose despite an increase in the KAP.

In the aneurysm patients, the lens dose was weakly cor-related with the FT/AK. It was strongly correlated with the KAP, especially that for a lateral X-ray tube. The frontal X-ray tube used for cerebral endovascular treatment in our hospital is installed on the dorsal side of each patient, and its lateral X-ray tube is installed on the left side of each patient. The left eye lens is located on the side of a lateral X-ray tube, and on the side of a frontal FPD. It is exposed to X-ray before human-body permeation in the lateral direction, and after human-body permeation in the frontal direction. There-fore, it may have been markedly influenced by scattered radiation related to lateral-direction X-ray. In endovascular

According to a report published by Sato et al.,14) the direc-tional dependency of a MOSFET dosimeter showed an approximately 20% reduction in the sensitivity in the axial direction. When a dosimeter is placed on the eyelid from the lateral side of the left eye, X-ray from a lateral X-ray tube is axial to the dosimeter; therefore, the dose may be underestimated. The error of the directional dependency of an SOF, which was used in this study, was ≤5%, excluding that at a caudal angle of 60°. When a dosimeter is placed from the caudal side toward the head side in clinical prac-tice, the patient or table interferes with the C-arm at a deep angle (caudal angle of ≥60°); it is not realistic. In this study, the working angles ranged from left anterior oblique (LAO) 99° to right anterior oblique (RAO) 128° and from cranial 38° to caudal 46°; there may have been no influence of directional dependency.

The dose of an SOF showed linearity with changes in the irradiation time. An SOF may be clinically useful during a procedure that may require many hours, such as cerebral endovascular treatment. However, the automatic exposure control may increase the tube voltage if a high dose is required. Therefore, the dose may be underesti-mated due to the energy dependency of an SOF. In this study, the maximum tube voltage was 125 kV; the dose may have been underestimated by approximately 23%.

There was no significant difference in the lens dose between the AVM/CCF and aneurysm patients. The KAP,

Fig. 5 (a) Mean lens dose with respect to the frequency of CTLI and comparison of the FT (b) AK, (c) KAP, and (d) among the groups. AK: air kerma; CTLI: CT-like image; FT: fluoroscopic time; IRP: interven-tional reference point; KAP: kerma area product


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during 3-year post-treatment follow-up exceeded 0.5 Gy, which is the threshold dose of lens opacity. The eye lens is one of the tissues of which the radiation sensitivity is high, and radiation exposure induces cataract. Cataract is pri-marily classified into three types based on the site of lens opacity: cortical cataract, nuclear cataract, and posterior sub-capsular cataract. Frequent sites depend on etiological factors. Age-related cataract is primarily cortical or nuclear cataract. Radiation cataract is primarily posterior subcap-sular cataract.6) Concerning the pathogenesis of radiation exposure-related posterior subcapsular cataract, the germi-native-zone epithelial cells with a high division potential may differentiate into fibrocytes when damaged by radia-tion, and migrate to the posterior capsular side, leading to cataract through crystalline aggregation at the same site.20) The radiation responses of some lens epithelial cells may occur a few months after exposure, whereas those of other lens epithelial cells may appear after 20–30 years. Further-more, the lens continues to proliferate over the lifetime, but it is surrounded by the lens capsule; therefore, all cells remain in the lens regardless of survival/death, comprising a closure system.21) Radiation-related lens damage may be accumulated over the lifetime; therefore, it is ideal to man-age lens exposure in each patient through all examinations/modalities. In this study, the KAP value was the most strongly correlated with the lens dose. However, the energy of X-ray varies among different imaging conditions, and the scattered ray dose differs among devices/institutions. Therefore, the approximate equation obtained in this study cannot be applied to the values displayed on the systems in other institutions. It may be difficult to estimate the lens dose based on the value displayed on the system. Cur-rently, it may be important to evaluate the current state of lens exposure and make efforts to reduce exposure.

Conclusion

In the patients with aneurysms, there was a strong correla-tion between the KAP value and lens dose. The lens dose slightly increased with an increase in the field of irradia-tion. As imaging conditions differ among devices/institu-tions, it is difficult to estimate the lens dose based on the value displayed on the system. The influence of CTL imag-ing on the lens dose was the most marked. If the radiation dose on CTL imaging can be reduced, the lens dose during cerebral endovascular treatment may be reduced. In the future, lens exposure dose-managing methods using Radi-ation Dose Structured Report should be examined.

treatment procedures, a reduction in the magnification rate for the field of irradiation is useful for reducing the patient skin dose.16,17) When the field of irradiation is reduced, the radiation dose increases through the automatic exposure control. Furthermore, the maximum entrance skin dose is influenced by X-ray that directly enters.18) However, when comparing the field of irradiation, the lens dose was slightly higher in the wide group. For imaging at a working angle, the site of treatment is located at the isocenter. Furthermore, in this study, we confirmed that lateral X-ray images did not involve the orbit after the establishment of a working angle in most patients. On a view from the lateral direction, the lens is located on the outside of the irradiation field, and an increase in the field of irradiation may have reduced the distance between the lens and margin of the irradiation field. Considering that the influence of a lateral X-ray tube is more marked than that of a frontal X-ray tube, the lens dose may be influenced by scattered radiation that generates with an increase in the subject’s scattered volume.

The lens dose per session of CTL imaging was four times higher than that per session of 3D-DSA. The AK dis-played on the system per session of CTL imaging was 3.8 times higher than that per session of 3D-DSA, reflect-ing a difference in X-ray output. 3D-DSA facilitates the visualization of high-contrast medium, whereas CTL imag-ing facilitates the visualization of low-contrast parenchy-mal organs. Therefore, CTL imaging requires a higher radiation dose. If the radiation dose on CTL imaging can be reduced, the lens entrance dose during cerebral endovascu-lar treatment may be reduced.

In this study, there was no patient with a lens dose exceed-ing 500 mGy during a single session of cerebral endovascu-lar treatment. According to a report published by Kawauchi et al.,15) the mean lens dose during a single session of diag-nostic cerebral angiography was 58.5 mGy. In our study, the mean lens dose during cerebral endovascular treatment was 78.0 mGy, being higher than during diagnostic angiography. On cerebral endovascular treatment, differing from diagnos-tic angiography, imaging is repeated at a working angle. Fur-thermore, patients in whom CTL imaging was performed were included, and this may have contributed to the high lens dose during cerebral endovascular treatment. In most patients undergoing cerebral endovascular treatment, preop-erative diagnostic or postoperative follow-up angiography or CT is performed. Seguchi et al.19) investigated radio-logical diagnosis-/treatment-/follow-up-related radiation exposure in patients with cerebral aneurysms in a phantom experiment and reported that the cumulative lens dose


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9) Jaco JW, Miller DL: Measuring and monitoring radiation dose during fluoroscopically guided procedures. Tech Vasc Interv Radiol 2010; 13: 188–193.

10) Hayakawa M, Moritake T, Kataoka F, et al: Direct mea-surement of patient’s entrance skin dose during neurointer-ventional procedure to avoid further radiation-induced skin injuries. Clin Neurol Neurosurg 2010; 112: 530–536.

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13) Safari MJ, Wong JH, Kadir KA, et al: Real-time eye lens dose monitoring during cerebral angiography procedures. Eur Radiol 2016; 26: 79–86.

14) Sato F, Honda T, Haga Y, et al: [Basic characteristic evalua-tion of the Real-time model MOSFET dosimeter]. Bull Sch Health Sci Tohoku Univ 2017; 26: 57–65. (in Japanese)

15) Kawauchi S, Moritake T, Hayakawa M, et al: [Estima-tion of maximum entrance skin dose during cerebral angiography]. Jpn J Radiol Technol 2015; 71: 746–757. (in Japanese)

16) Miller DL, Balter S, Cole PE, et al: Radiation doses in interventional radiology procedures: the RAD-IR study: part I: overall measures of dose. J Vasc Interv Radiol 2003; 14: 711–727.

17) Miller DL, Balter S, Cole PE, et al: Radiation doses in interventional radiology procedures: the RAD-IR study: part II: skin dose. J Vasc Interv Radiol 2003; 14: 977–990.

18) Safari MJ, Wong JHD, Jong WL, et al: Influence of expo-sure and geometric parameters on absorbed doses associ-ated with common neuro-interventional procedures. Phys Med 2017; 35: 66–72.

19) Seguchi S, Saijou T, Ishikawa Y, et al: [Radiation dose to patients undergoing X-ray diagnosis, treatment and follow-up for cerebral aneurysms]. No Shinkei Geka 2015; 43: 411–418.

20) Sasaki H: Radiation cataract. Jpn J Clin Ophthalmol 2014; 68: 1667–1672.

21) Hamada N, Fujimichi Y: [What happens in normal human lens epithelial cells exposed to ionizing radiation?] Isotope News 2015; 734: 7–11. (in Japanese)

Acknowledgment

We deeply thank Mr. Kazushige Yui (Acrobio Corporation) who lent the scintillation optical fiber dosimeter for this research.

Disclosure Statement

There is no conflict of interest for the first author and coauthors.

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