Radiation exposure of the radiologist’s eye lens during CT-guided interventions

Abstract

Background

In the past decade the number of computed tomography (CT)-guided procedures performed by interventional radiologists have increased, leading to a significantly higher radiation exposure of the interventionalist’s eye lens. Because of growing concern that there is a stochastic effect for the development of lens opacification, eye lens dose reduction for operators and patients should be of maximal interest.

Purpose

To determine the interventionalist’s equivalent eye lens dose during CT-guided interventions and to relate the results to the maximum of the recommended equivalent dose limit.

Material and Methods

During 89 CT-guided interventions (e.g. biopsies, drainage procedures, etc.) measurements of eye lens’ radiation doses were obtained from a dedicated dosimeter system for scattered radiation. The sensor of the personal dosimeter system was clipped onto the side of the lead glasses which was located nearest to the CT gantry. After the procedure, radiation dose (µSv), dose rate (µSv/min) and the total exposure time (s) were recorded.

Results

For all 89 interventions, the median total exposure lens dose was 3.3 µSv (range, 0.03–218.9 µSv) for a median exposure time of 26.2 s (range, 1.1–94.0 s). The median dose rate was 13.9 µSv/min (range, 1.1–335.5 µSv/min).

Conclusion

Estimating 50–200 CT-guided interventions per year performed by one interventionalist, the median dose of the eye lens of the interventional radiologist does not exceed the maximum of the ICRP-recommended equivalent eye lens dose limit of 20 mSv per year.

Keywords

Dose eye lens radiation exposure CT-guided interventions

Introduction

The use of computed tomography (CT) has grown rapidly over the past decades. In particular, the number of CT-guided interventions for diagnostic and therapeutic purposes (e.g. drainages, biopsies) has increased significantly (1).

Patients with radiation exposure due to CT investigations exhibit an increased incidence of cataract disease (2 –4). The eye lens is one of the most radiosensitive organs of the human body. A threshold of 2 Gy was recently considered critical to cause cataracts following acute radiation in patients. A cumulative dose of 4 Gy over 3 months was reported as particularly damaging for lenses (5). In recent years even lower radiation exposure has been suspected to induce cataracts (6 –8). Klein et al. reported lens opacification without loss of vision following radiation exposure of doses as low as 0.2 Gy (9). Previous recommendations of the International Commission on Radiological Protection (ICRP) were based on the assumption that the development of cataract occurs only above a certain threshold. However, there is growing concern that there is also a stochastic effect for the development of lens opacification (8,10 –12). Based on emerging epidemiological evidence, the ICRP issued a statement on tissue reaction, in which the recommended equivalent dose limit for the eye lens is now 20 mSv per year, averaged over a defined period of 5 years, with no single year exceeding 50 mSv. For acute exposure the threshold is now considered to be 0.5 Gy (13). In Germany, the defined dose limit to the eye lens is still 150 mSv/a. ICRP stated in paragraph A 80 of ICRP 103 that it cannot ultimately be excluded that a cataract can be induced at even lower doses, and this notion is supported by recent studies (7,12).

Only few studies have analyzed the dose to the lens of medical staff in interventional radiology and cardiology so far, and there are only few data on the respective risk of lens opacification and cataract formation (11,14). For interventionalists with a high number of procedures a second body dosimeter is recommended at the level of the collar in order to assess the organ dose to the eye (15). Radiation-induced cataracts in interventionalists and lens doses approaching the traditional limit of 150 mSv per year during angiographic procedures have been reported (16,17).

For simple CT examinations the interventionalist does not necessarily need to be within the controlled radiation area, but complex CT-guided interventions may require direct contact to the patient and participation of the investigator (18,19).

Hence, the purpose of this study was to evaluate the interventionalist’s equivalent eye lens dose during CT-guided interventions and to relate the results to the maximum of the recommended equivalent dose limit.

Material and Methods

Patients

Data from 89 CT-guided interventions (e.g. biopsies, drainage procedures, sympathicolysis) between August 2011 and March 2012 were retrospectively analyzed. Written informed consent was obtained from all participants. Patients (32 women, 57 men, mean age 61.4 ± 13.4 years) were referred from different departments of our tertiary care University Hospital for CT-guided interventions.

Dosimetry

Measurements of eye lens doses were obtained from a dedicated dosimeter system for scattered radiation (Unfors EED-30; Unfors Instruments, Billdal, Sweden), which consists of a solid-state 6 × 11 × 22-mm sensor calibrated for use in the diagnostic X-ray energy range and a display unit. The sensor has a spherical response, which is capable of measuring the dose independently of the incident angle of radiation (Fig. 1). This instrument allows the measurement of dose rate ranges between 0.03 mSv/h and 2.00 Sv/h. At the 95% confidence level the total traceable uncertainty for the calibration is ± 6%. The personal dosimeter used is calibrated in terms of Hp (0.07).

Fig. 1.

The personal dosimeter system used for measurement of the scattered radiation to the interventionalists eye lens (Unfors EED-30; Unfors Instruments, Billdal, Sweden), which consists of a solid-state 6 × 11 × 22-mm sensor calibrated for use in the diagnostic X-ray energy range and a display unit.

The sensor of the personal dosimeter system was clipped onto the side of the lead glasses which was located nearest to the CT gantry (Fig. 2). During CT measurements the interventionalist positioned himself next to the CT gantry to minimize radiation exposure. Because of complex interventions in clinical routine the position of the operator could not be absolutely standardized. After the procedure, radiation dose (µSv), dose rate (µSv/min), and the total exposure time (s) were recorded. The dose rate range was 0.03 mSv/h to 2 Sv/h. Exposure time is the total accumulated time where the sensor signal is above the end trigger level after first exceeding the start trigger level.

Fig. 2.

Two radiologists during CT-guided drainage procedure. The personal dosimeter system was clipped onto the side of the lead glass which is located nearest to the CT gantry.

Data are presented as median (range).

CT-guided interventions

All procedures were performed on a 6-detector row multidetector computed tomography (MDCT) scanner (Emotion 6, Siemens AG, Erlangen, Germany). Depending on the intervention the procedure was performed in supine, lateral, or prone position. An unenhanced MDCT was acquired for planning with the patient positioned appropriately for the interventional procedure (100 KV, 100 mAs, 3 mm slice thickness, 1.2 mm reconstruction increment, pitch 1.2). Medical staff was not present in the CT room during acquisition of the planning scan. Interventions were performed by three radiologists with 6, 9, and 25 years of experience in CT-guided interventions, respectively. Optimal localization for skin incision was determined by the CT data and marked on the skin. According to the intervention, different needle and drainage systems were used. An intermittent CT-fluoroscopy mode (110 kV, 80 mAs, 6 mm slice thickness) (CareVision®, Siemens Medical Care, Erlangen, Germany) was used to control the needle or catheter position and direction. The table position was controlled by the radiologist under sterile conditions using a joystick attached to the table. Image acquisition was controlled with a foot pedal. CT-fluoroscopy images were displayed on a monitor next to the patient table directly facing the interventional radiologist. To exclude complications an unenhanced low-dose MDCT scan of the region of interest was performed after the intervention.

Results

Twenty-nine of 89 interventions were CT-guided biopsies. The median lens dose for these biopsies was 3.9 µSv (range, 0.5–218.9 µSv) for a median exposition time of 17.7 s (range, 1.8–335.5 s). The median dose rate for biopsies was 26.8 µSv/min (range, 1.3–52.0 µSv/min) (Table 1).

Table 1.

Median (range) total exposure of the eye lens (µSv), the median exposure time (s), and the median dose rate (µSv/min) for CT-guided biopsies (n = 29), CT-guided drainage procedures (n = 41), and other CT-guided interventions (n = 19).

Median total exposure lens dose (µSv)	Median exposure time (s)	Dose rate (µSv/min)
CT-guided biopsies (n = 29)	3.9 (0.5–218.9)	17.7 (1.8–335.5)	26.8 (1.3–52.0)
Drainage procedures (n = 41)	1.9 (0.03–52.6)	21.4 (1.2–68.7)	13.9 (1.1–175.3)
Others (n = 19) (i.e. sympathicolysis, lung nodule marking)	3.5 (0.2–39.9)	35.1 (1.1–59.5)	12.8 (2.2–208.5)

Forty-one different drainage procedures were performed with a median lens dose of 1.9 µSv (range, 0.03–52.6 µSv), a median dose rate of 13.9 µSv/min (range, 1.1–175.3 µSv/min) and a median exposure time of 21.4 s (range, 1.2–68.7 s) (Table 1).

Nineteen other CT-guided interventions (i.e. sympathicolysis, preoperative lung nodule marking) resulted in a median lens dose of 3.5 µSv (range, 0.2–39.9 µSv), a median dose rate of 12.8 µSv/min (range, 2.2–208.5 µSv/min) and a median exposure time of 35.1 s (range, 1.1–59.5 s) (Table 1).

Discussion

The use of CT as a guidance tool for complex percutaneous interventions has increased tremendously over the past years in clinical routine (20). Hence, interventional radiologists are exposed to a considerable amount of scattered radiation while standing next to the patient during the intervention (21). In general, radiation exposure in CT interventions should follow the term “as low as reasonable achievable” (ALARA-principle), especially because exposure times during CT-guided procedures can be long compared with diagnostic CT acquisitions (22). In interventional cardiology a recent multicenter study has compared the prevalence of different stages and types of cataracts in an exposed group of interventional cardiologists with an unexposed control group of non-interventional cardiologists, while taking into account other risk factors for cataracts, use of radiation protection tools, and exposure level (6). Other investigators previously demonstrated the amount of radiation dose to the operator’s eye lens during different conventional fluoroscopy and angiographic procedures of up to mean dose of 0.085 mSv (16,23 –26). However, data on the radiation exposure of the radiologist’s eye lens during CT-guided interventions are still lacking. Therefore, the aim of this study was to evaluate the interventionalists’ equivalent eye lens doses during CT-guided interventions in clinical routine. Our results demonstrate that the scattered radiation exposure to the interventionalists’ eye lens, estimating 50–200 CT-guided interventions per year (0.17–0.67 mSv/a), is far away from exceeding the maximum of the recommended equivalent dose limit for the eye lens of 20 mSv per year. It has to be kept in mind, however, that an interventional radiologist may perform many other interventions with even higher radiation exposure to the eye lens besides CT-guided interventions during 1 year.

Our study has some limitations. The personal dosimeter used is calibrated in terms of the dose equivalent in soft tissue at 0.07 mm below body surface (H_p 0.07). For measuring radiation dose of the eye lens the IRCP recommends dosimeters calibrated in terms of H_p (3). This effect seems to be negligible, because the use of dosimeters calibrated in terms H_p (0.07) results in a systematic overestimation of the radiation exposure to the eye lens by 10% or even less (27).

Another limitation is that scattered radiation measurements of the eye lens of three different radiologists with variable experience in CT-guided interventions were included in this study. Although trying to follow the ALARA-principle the position of the interventionalist could not be standardized due to complex intervention procedures in clinical routine.

In conclusion, estimating 50–200 CT-guided interventions per year performed by one operator, the median dose of the eye lens of the interventional radiologist does not exceed the maximum of the recommended equivalent dose limit for the eye lens of 20 mSv per year. In view of the fact that there might be a non-deterministic effect for the development of eye lens opacification caused by radiation exposure there still should be maximal interest in dose reduction for operators as well as for patients.

Footnotes

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

References

Carlson

Bender

Classic

. Benefits and safety of CT fluoroscopy in interventional radiologic procedures. Radiology 2001; 219: 515–520.

Schmitz-Feuerhake

Pflugbeil

. Radiation risks from diagnostic radiology: meningiomas and other late effects after exposure of the skull. Gesundheitswesen 2010; 72: 246–254.

Dammann

Momino-Traserra

Remy

. Radiation exposure during spiral-CT of the paranasal sinuses. RoFo 2000; 172: 232–237.

Michel

Jacob

Roger

. Eye lens radiation exposure and repeated head CT scans: A problem to keep in mind. Eur J Radiol 2011; 81: 1896–1900.

Valentin

. Avoidance of radiation injuries from medical interventional procedures. Ann ICRP 2000; 30: 7–67.

Jacob

Michel

Spaulding

. Occupational cataracts and lens opacities in interventional cardiology (O'CLOC study): are X-Rays involved? Radiation-induced cataracts and lens opacities. BMC Public Health 2010; 10: 537–537.

Worgul

Kundiyev

Sergiyenko

. Cataracts among Chernobyl clean-up workers: implications regarding permissible eye exposures. Radiat Res 2007; 167: 233–243.

Shore

Neriishi

Nakashima

. Epidemiological studies of cataract risk at low to moderate radiation doses: (not) seeing is believing. Radiat Res 2010; 174: 889–894.

Klein

Linton

. Diagnostic x-ray exposure and lens opacities: the Beaver Dam Eye Study. Am J Public Health 1993; 83: 588–590.

10.

Ainsbury

Bouffler

Dörr

. Radiation cataractogenesis: a review of recent studies. Radiat Res 2009; 172: 1–9.

11.

Rehani

Vano

Ciraj-Bjelac

. Radiation and cataract. Radiat Prot Dosimetry 2011; 147: 300–304.

12.

Chodick

Bekiroglu

Hauptmann

. Risk of cataract after exposure to low doses of ionizing radiation: a 20-year prospective cohort study among US radiologic technologists. Am J Epidemiol 2008; 168: 620–631.

13.

International Commission on Radiological Protection. Statement on tissue reactions. IRCP ref 4825-3093-1464. 2011. http://www.ircp.org.

14.

Vano

Kleiman

Duran

. Radiation cataract risk in interventional cardiology personnel. Radiat Res 2010; 174: 490–495.

15.

Martin

. A review of radiology staff doses and dose monitoring requirements. Radiat Prot Dosimetry 2009; 136: 140–157.

16.

Vano

Gonzalez

Fernández

. Eye lens exposure to radiation in interventional suites: caution is warranted. Radiology 2008; 248: 945–953.

17.

Pages

. Effective dose and dose to the crystalline lens during angiographic procedures. JBR-BTR 2000; 83: 108–110.

18.

Silverman

Tuncali

Adams

. CT fluoroscopy-guided abdominal interventions: techniques, results, and radiation exposure. Radiology 1999; 212: 673–681.

19.

Nawfel

Judy

Silverman

. Patient and personnel exposure during CT fluoroscopy-guided interventional procedures. Radiology 2000; 216: 180–184.

20.

Buls

Pagés

de Mey

. Evaluation of patient and staff doses during various CT fluoroscopy guided interventions. Health Physics 2003; 85: 165–173.

21.

Miller

Vañó

Bartal

. Occupational radiation protection in interventional radiology: a joint guideline of the Cardiovascular and Interventional Radiology Society of Europe and the Society of Interventional Radiology. Cardiovasc Intervent Radiol 2010; 33: 230–239.

22.

Joemai

Zweers

Obermann

. Assessment of patient and occupational dose in established and new applications of MDCT fluoroscopy. Am J Roentgenol 2009; 192: 881–886.

23.

Sandborg

Rossitti

Pettersson

. Local skin and eye lens equivalent doses in interventional neuroradiology. Eur Radiol 2010; 20: 725–733.

24.

Schulz

Heidenreich

. Radiation exposure to operating staff during rotational flat-panel angiography and C-arm cone beam computed tomography (CT) applications. Eur J Radiol 2012; 81: 4138–4142.

25.

Domienik

Brodecki

Carinou

. Extremity and eye lens doses in interventional radiology and cardiology procedures: first results of the ORAMED project. Radiat Prot Dosimetry 2011; 144: 442–447.

26.

Efstathopoulos

Pantos

Andreou

. Occupational radiation doses to the extremities and the eyes in interventional radiology and cardiology procedures. Br J Radiol 2011; 84: 70–77.

27.

Behrens

Dietze

. Monitoring the eye lens: which dose quantity is adequate? Phys Med Biol. 2010 55: 4047–4062.