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Efficiency of radiation protection equipment in interventional radiology: a systematic Monte Carlo study of eye lens and whole body doses To cite this article: C Koukorava et al 2014 J. Radiol. Prot. 34 509

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- Monte Carlo study of the scattered radiation field near the eyes of the operator in interventional procedures Paolo Ferrari, Frank Becker, Eleftheria Carinou et al. - Eye lens monitoring for interventional radiology personnel: dosemeters, calibration and practical aspects of Hp(3) monitoring. A 2015 review Eleftheria Carinou, Paolo Ferrari, Olivera Ciraj Bjelac et al. - Derivation and application of dose reduction factors for protective eyewear worn in interventional radiology and cardiology Jill S Magee, Colin J Martin, Viktor Sandblom et al.

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Society for Radiological Protection J. Radiol. Prot. 34 (2014) 509–528

Journal of Radiological Protection doi:10.1088/0952-4746/34/3/509

Efficiency of radiation protection equipment in interventional radiology: a systematic Monte Carlo study of eye lens and whole body doses C Koukorava1,2, J Farah3, L Struelens4, I Clairand3, L Donadille3, F Vanhavere4 and P Dimitriou2 1

  Greek Atomic Energy Commission, Division of Licensing and Inspections, PO Box 60092, Ag. Paraskevi 15310 Athens, Greece 2   Department of Medical Physics, University of Athens, Medical School, Athens, Greece 3   Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Human Health Division, BP-17, 92262 Fontenay-aux-Roses Cedex, France 4   Belgian Nuclear Research Centre, Department of Radiation Protection Dosimetry and Calibration, Boeretang 200, BE-2400 Mol, Belgium Email: [email protected] Received 9 July 2013, revised 10 April 2014 Accepted for publication 30 April 2014 Published 18 June 2014 Abstract

Monte Carlo calculations were used to investigate the efficiency of radiation protection equipment in reducing eye and whole body doses during fluoroscopically guided interventional procedures. Eye lens doses were determined considering different models of eyewear with various shapes, sizes and lead thickness. The origin of scattered radiation reaching the eyes was also assessed to explain the variation in the protection efficiency of the different eyewear models with exposure conditions. The work also investigates the variation of eye and whole body doses with ceiling-suspended shields of various shapes and positioning. For all simulations, a broad spectrum of configurations typical for most interventional procedures was considered. Calculations showed that ‘wrap around’ glasses are the most efficient eyewear models reducing, on average, the dose by 74% and 21% for the left and right eyes respectively. The air gap between the glasses and the eyes was found to be the primary source of scattered radiation reaching the eyes. The ceilingsuspended screens were more efficient when positioned close to the patient’s skin and to the x-ray field. With the use of such shields, the Hp(10) values recorded at the collar, chest and waist level and the Hp(3) values for both eyes were reduced on average by 47%, 37%, 20% and 56% respectively. Finally, 0952-4746/14/030509+20$33.00  © 2014 IOP Publishing Ltd  Printed in the UK

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simulations proved that beam quality and lead thickness have little influence on eye dose while beam projection, the position and head orientation of the operator as well as the distance between the image detector and the patient are key parameters affecting eye and whole body doses. (Some figures may appear in colour only in the online journal)

1. Introduction Radiation-induced lens opacities and cataract formation are of particular concern to the scientific community since recent epidemiological studies have shown that lens opacities may appear for doses lower than previously considered (Worgul et al 2007, Chodick et al 2008). A category of occupationally exposed personnel that is of particular concern are the interventional radiologists and cardiologists since they work close to the patient while performing prolonged fluoroscopically guided procedures. Moreover, some authors have shown that such procedures are often conducted without the use of the appropriate radiation protective equipment or with an inappropriate use of the latter (Vano et al 1998a, 1998b, Whitby et al 2005, Lie et al 2008, Carinou et al 2011, Donadille et al 2011, Nikodemova et al 2011). Previous measurements of eye lens dose, performed on physicians during interventional radiology (IR) and cardiology (IC) procedures, and several studies assessing retrospectively cumulative eye lens doses, have shown that the new annual limit of 20 mSv recommended by the ICRP (ICRP 2012) can be exceeded in numerous cases (Lie et al 2008, Dauer et al 2010, Vanhavere et al 2011, Jacob et al 2013). Moreover, recent surveys indicate a significantly elevated prevalence of lens opacities to those medical professionals (Ciraj-Bjelac et al 2010, Vano et al 2010, 2013) confirming this concern and increasing the need for specific monitoring of the eye lens dose as well as systematic and appropriate use of radiation protective equipment in standard clinical conditions. Several studies, based on measurements performed either on phantoms or on physicians during their clinical practice, stress the importance of protective equipment, such as ceiling-­ suspended shields and lead glasses (Maeder et al 2006, Vano et al 2008, Carinou et al 2011, Koukorava et al 2011b, McVey et al 2013, Sturchio et al 2013, Van Rooijen et al 2013). This was also confirmed by an extended simulation campaign performed within the European ORAMED project (2008–2011, European 7th Framework Program). Dose reduction of up to 90% to the left eye lens was reported with the use of lead glasses and up to 93% for both eyes with the use of ceiling-suspended screens (Koukorava et al 2011a). However, a very challenging issue for fluoroscopically guided procedures is the extremely wide range of configurations to which the operator is exposed. Not only do the energy and orientation of the beam change during a specific procedure, but also the position of the operator with respect to the radiation field will vary from one procedure to the other. Most of the previously published studies have selected some specific exposure conditions to investigate the effect of the protective equipment on the eye lens dose. Van Rooijen et al (2013), McVey et al (2013) and Sturchio et al (2013) all performed eye lens dose measurements on a Rando–Alderson phantom considering one typical x-ray beam energy and projection, while varying the position and orientation of the operator towards the x-ray field. While in the study of McVey et  al one type of glasses was tested, three and five different commercially available lead glasses were considered in the studies of Sturchio et al and Van Rooijen et al, respectively. The most realistic results will obviously be obtained from measurements performed on the 510

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operators in clinical practice, as was done by Maeder et al (2006) and Vanhavere et al (2011). Maeder et al found a dose reduction to the eyes by a factor of 19 if a ceiling-suspended shield is used. Meanwhile, Vanhavere et al reported a dose to the eyes reduction factor ranging from 2 to 7 with a ceiling shield, depending on the type of procedure. Nonetheless, performing such measurements in routine practice is not straightforward since it is difficult to properly place a dosemeter behind the lead glasses without disturbing the vision of the operator. Therefore, the above-cited studies used correction coefficients accounting for the use of lead glasses, derived from Monte Carlo (MC) simulations or measurements on phantoms. Finally, a few studies also suggested that the amount of scattered radiation reaching the eyes may directly be related to how well the lead glasses fit on the face of the operator (Geber et al 2011, Sturchio et al 2013, Van Rooijen et al 2013). The goal of this study is to extend all previous studies by performing a systematic investigation of the variation of eye lens dose by conducting an extensive simulation campaign. The advantage of performing simulations, compared to measurements on phantoms, is that a large range of parameters and configurations can be considered and investigated separately. Moreover, the origin of the scattered radiation that reaches the eyes is investigated for the different considered configurations. Whereas in clinical situations many parameters will simultaneously change during a procedure, individual simulations of each parameter will help in understanding why the efficiency of lead glasses can vary from one situation to another. The conducted MC simulations, studying the variation of eye lens dose, included: - different models, shapes and lead thicknesses of the protective lead glasses; - different positions of the lead glasses on the face of the operator; - various shapes and positions of the ceiling-suspended shields with respect to the operator, the patient and the image detector (ID); - a large range of x-ray beam projections, including biplanar x-ray systems; - different x-ray beam qualities; - several distances of the ID with respect to the patient; - multiple positions of the operator and different head orientations with respect to the x-ray field. As a result of these simulations, which consider the most common routine parameters, an average dose reduction factor is derived to account for the use of lead glasses. The variation in the radiation protection efficiency of lead glasses is also studied in a large number of configurations. Moreover, since the ceiling-suspended screens protect not only the eyes but also the upper part of the body of the operator, their effect on whole body (WB) doses (in terms of Hp(10)) was also evaluated with MC simulations considering different possible wearing positions of the WB dosemeters (at the collar, chest and waist levels) above the lead apron. Overall, the importance of correct use of the available protective equipment is highlighted and methods for more efficient protection are suggested. 2.  Materials and methods 2.1.  Simulation setup and configuration

The MCNPX v.2.5 Monte Carlo code was used for the present study (Pelowitz 2005). A basic but realistic geometry representing an IR/IC procedure was used where the patient and the 511

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Figure 1. Positions of the whole body dosemeters on the operator phantom (R—right, M—middle, L—left).

operator are represented by two modified anthropomorphic ORNL–MIRD phantoms (Snyder et al 1978). Detailed description of the MC model of the clinical setup and the phantoms used is presented in a previous publication (Koukorava et al 2011a). This MC model was however upgraded for the purpose of this study. First, in order to investigate the effect of the ceiling shields on WB doses, WB dosemeters represented by 4 × 4 cm2 and 10 mm thick cells were added to the operator phantom. These were modeled above the lead apron on the left, middle and right side of the trunk at the collar, chest and waist levels (figure 1). Moreover, very thin (0.004 mm) tally volumes were positioned at 3 mm depth within the eye cells for the calculation of Hp(3) and at 10 mm depth inside the cells representing the WB dosemeters for the calculation of Hp(10). Besides, in order to improve the efficiency of the runs for the eye lens and WB dose calculations, two DXTRAN spheres, a variance reduction method, were defined: one surrounding the eyes of the operator and a second at the level of the torso surrounding the WB dosemeters. The number of histories was chosen according to the irradiation conditions but generally was of the order of 108, keeping the statistical uncertainty below 3% for the calculations of Hp(3) and below 10% for Hp(10). All doses were calculated using the energy deposition tally in kerma approximation (F6 tally). These were normalized to the dose at the entrance of the ID since this parameter remains constant on clinically used fluoroscopic systems using the automatic exposure control system (AEC).

2.2.  Protection efficiency of lead glasses

In order to evaluate the influence of the lead glasses on eye lens doses, two commonly used eyewear models were simulated: • one ‘wrap around’ type with 0.5 mm lead thickness (L1, figure 2(a)) • one with rectangular front lenses (0.75 mm Pb) and side protection (0.3 mm Pb) (L2, figure 2(b)). An additional modification was introduced to the L2 model by tilting the front lenses towards the head by 10° (L2′, figure 2(c)). 512

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L1

lens size 7.5 cm

L2 L

L2 side protection 4 cm

(a)

(c)

(b)

lens ssize 5.5 ccm

side protection 1.5 cm

(e)

(d)) eye lens 1 cm gap

0.5 cm ggap

(ff)

L1 1 type lead glasses

minimum) gap 0.6 cm (m

(ii)

(g)

1 cm gap

L2 2 type lead glassses

1.5 cm m gap

(h) 1.5 cm m gap

(j)

((k)

Figure 2. (a) ‘Wrap around’ type glasses (L1), (b) glasses with rectangular front lenses

and side protection (L2), (c) rectangular glasses with tilted front lenses (L2′), (d) L1 type glasses with small lenses, (b, e) L2 type glasses with large and small size of side protection, (f–k) different wearing positions of the glasses on the head and the respective air gaps between the head and the glasses. The dashed arrow (f) shows the eye lens cell used for the calculation of Hp(3).

The lead thickness of the L1 and L2 model was also modified as follows: • L1: 0.35 mm and 0.5 mm • L2: front/side of 0.75 mm/0.3 mm; 0.35 mm/0.35 mm; 0.75 mm/0.7 mm Also the size of the lens for the L1 model and the size of the side protection for the L2 model were changed: • L1: lens sizes from 5.5 cm (small) to 7.5 cm (large) (figures 2(a) and 2(d)) • L2: side sizes from 1.5 cm (small) to 4.0 cm (large) (figures 2(b) and 2(e)) The models considered in this study were verified against the technical specifications given by manufacturers for many available lead glasses. Finally, the way the lead glasses fit on the face of the operator was also tested by varying the air gap between the glasses and the operator’s head, as follows: • L1: air gaps of 0.5 cm (reference); 1.0 cm and 1.5 cm (figures 2(f), 2(g) and 2(h)) • L2: air gaps of 0.6 cm; 1.0 cm (reference) and 1.5 cm (figures 2(i), 2(j) and 2(k)) 513

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RLAT

LLAT RAO

z

CRAN

LAO z

PA y

PA x

Figure 3. Model used for the simulations and beam projections. The operator stands on

the right side of the patient.

2.3.  Exposure conditions

The radiation protection efficiency of the different eyewear models was studied in different exposure conditions. The following aspects were considered:

• Beam quality: – 70 kVp/3 mm Al (half value layer, HVL = 2.7 mm Al); – 80 kVp/3 mm Al (HVL = 3.1 mm Al); – 80 kVp/4 mm Al/0.2 mm Cu (HVL = 5.8 mm Al); – 90 kVp/3 mmAl (HVL = 3.5 mm Al) and – 100 kVp/3 mm Al (HVL = 3.9 mmAl).

• Beam projection: – Single-plane set up: postero-anterior (PA), left lateral (LLAT), right lateral (RLAT), cranial (CRAN), – Biplanar setup: PA+LLAT, PA+RLAT, left anterior oblique (LAO) 45° + right anterior oblique (RAO) 45° The representation of these projections is given in figure 3. • Operator position with respect to the x-ray field. On one hand the distance of the operator to the x-ray field was considered: – For head irradiation: 70 cm, 90 cm and 110 cm (all representing femoral access) – For thorax irradiation: 0 cm (representing pacemaker and defibrillator implantations), 40 cm (radial access) and 70 cm (femoral access) On the other hand, the head orientation of the operator was changed: – operator’s head at 0° facing forward – operator’s head rotated 45° facing the x-ray tube – operator’s head rotated 45° away from the x-ray tube The effect of the lens size and side protection size of the different eyewear models was specifically tested for different orientations of the operator’s head, as the combination of these two aspects could be significant. For each parameter, the protection efficiency is calculated as the ratio of the eye lens dose with lead glasses to the eye lens dose without lead glasses. In general, the field size for the head irradiation was of 20 cm diameter for all projections. For the thorax irradiations, a 20 cm diameter field 514

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size was used for the LLAT and RLAT projections while a 30 cm diameter field was considered for all other projections. This field size is defined at the entrance of the ID. The source to skin distance (SSD) and the source to image detector distance (SID) were 60 cm and 90 cm respectively, except for the lateral projections of the thorax irradiation where the SID was of 110 cm. For all calculations, the operator distance to the x-ray field was set at 70 cm to simulate a femoral access with thorax irradiation and the head facing forward (0° orientation), except for those simulations investigating the efficiency of the protective equipment with different operator positions and head orientations. Finally, the reference beam quality was set to 90 kV and a 3.5 mm Al HVL. 2.4.  Investigating the origin of scattered photons

To further deepen our understanding and knowledge on eye lens dose, the MCNP ‘cell flagging’ option was used to determine the origin of the scattered photons that contribute to this dose. This option accounts for the particles that leave a designated cell and contribute to a tally; such particles are listed separately in addition to the normal total tally (Pelowitz 2005, MCNP v.5 Manual vol.2, 2003). The cell flagging option was thus used to study the origin of particles reaching the eye lenses while both eyewear models are used (L1 and L2) for different irradiation conditions. The work investigated the proportion of particles crossing the air gap beneath the lead glasses, those arriving from the air gap between the lenses of the glasses and finally particles scattering within the operator’s unprotected head and neck areas. To carry out these simulations, air cells covering the air gaps beneath the lead glasses and between the eyes were defined and flagged as well as the skin cells in the head and neck region. Finally, the cells representing the lead glasses were also flagged to define the amount of scattered radiation that crosses the eyewear and reaches the eyes. 2.5.  Protection efficiency of ceiling-suspended shields

Ceiling-suspended shields of various models, shapes and sizes exist and are also commonly used in routine practice to reduce operator’s exposure. However, since the operator has the possibility to position them differently, their efficiency in reducing exposure may significantly vary. Indeed, the screens may be positioned touching the patient or several centimetres above the body, they can be close to the operator or near the x-ray field and they can be tilted in different directions or just set straight. Thus, to investigate the effect of the ceiling-suspended shields on both eye lens and WB doses and look for their optimal positioning, several realistic scenarios were simulated (figure 4): • A1: arc type shield tilted towards the operator and positioned close to the patient’s body (3 cm above the skin) (figure 4(a)) • A2: same arc type shield positioned 15 cm above the patient’s skin (figure 4(b)) • B1: rectangular shield without tilt, positioned above the patient (~1 cm above the skin) (figure 4(c)) • B2: same rectangular shield positioned to the side of the operator (for lateral projections or biplanar techniques only) (figure 4(d)) Both shield types had a thickness of 0.5 mm Pb. The shields were tested for head and thorax irradiations with a respective operator distance to the irradiated field of 110 cm and 70 cm, and for different beam projections (PA, LLAT and biplanar PA+LLAT, PA+RLAT, LAO 45°+RAO 45°). For head irradiation, two additional scenarios were tested with the arc type shields positioned closer to the x-ray field rather than to the operator while considering a PA tube projection: A1′ (3 cm above the patient) and A2′ (15 cm above the patient). Those scenarios are shown together with A1 and A2 cases (figures 4(e) and 4(f)) respectively to point out the difference in shield positioning. 515

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small gap

large gap

A1

A2

70 cm

(a)

(b)

B1 B2

(c) shield close to x-ray field

(d) A1

A1

shield close to operator

A2

A2

110 cm

(e)

(f)

Figure 4. Models representing the shields A1 and A2 for PA projection (a, b), the B1 and

B2 for LLAT projection (c, d) for thorax irradiation and the A1, A2 (shield close to operator) and A1′, A2′ (shield close to x-ray field) (e, f) for PA projection and head irradiation.

2.6.  Influence of the ID position

Finally, the effect on eye lens doses of the distance between the ID and the patient’s skin was evaluated. A thorax irradiation was simulated considering a PA tube projection with the operator standing at the femur level of the patient. Four ID-patient’s skin distances were tested including namely 10 cm (considered as reference), 20 cm, 25 cm and 30 cm air gaps. Neither lead glasses nor ceiling-mounted shields were used for this test. 3. Results 3.1.  Protection efficiency of lead glasses 3.1.1.  The origin of the scattered photons.  Table 1 gives the contribution of the scattered radia-

tion hitting the lead glasses. For these calculations however, the lead material of the glasses was replaced by air since the primary objective was to determine where the scattered radiation is coming from and not how much radiation is attenuated by the glasses. The results are shown 516

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Table 1.  The contribution of that part of the scattered radiation reaching the eyes that

hits the lead glasses (lead material is replaced by air).

Type

Beam ­projection

Operator at 70 cm from x-ray field

Operator aligned with x-ray field (0 cm)

Left eye

Right eye

Left eye

Right eye

L1

PA LLAT RLAT

87% 89% 91%

12% 5% 60%

60%

51%

L2

PA LLAT RLAT

38% 20% 77%

22% 7% 73%

37%

40%

for both the L1 and L2 models. On the one hand, a thorax irradiation is considered with the operator at 70 cm from the x-ray field, for PA, LLAT and RLAT projections. On the other hand, the same calculation is performed for a thorax irradiation with direct access, where the operator is aligned with the centre of the x-ray field. In the case of L1 eyewear model, more than 85% of the scattered radiation that reaches the left eye hits the lead glasses, for all considered projections. This is not the case for the right eye where this contribution is very small for PA and LLAT projections. For the RLAT projection, however, a large part (60%) hits the lead glasses as well. For the L2 model, only a small part of the scattered radiation reaching the eyes hits the lead glasses; this is true for both left and right eyes and for both PA and LLAT projections. The situation is again different for the RLAT projection for which the largest contribution of the scattered radiation hits the lead glasses. When the operator stands near the x-ray field (i.e. aligned to the field centre), as for pacemaker or defibrillator implantation procedures, the amount of scattered radiation reaching both eyes for the L1 and L2 models is comparable and accounts for up to 40–60% of the total eye exposure with a PA projection, the most common tube projection for such procedures. In figures 5(a) and (b), the contribution to the left and right eye doses, respectively, is given for the scattered radiation originating from the unprotected parts, such as the air gaps beneath the glasses, the air gap between the left and right glasses (at the level of the nose) and the radiation backscattered from the head. For these calculations, the lead material of the glasses was again included. It is very clear that for the L2 model, the largest contribution to the eye lens dose, especially for the left eye, is due to scattered radiation passing through the air gaps beneath the glasses. The contribution of the radiation hitting the operator’s head and backscattered to the eyes is not negligible, especially for the LLAT projection in case of the right eye. The gap between the glasses mostly affects the right eye for the specific geometry (x-ray tube on the left side of the operator) for all tested projections and for both L1 and L2 types. Similar results were observed for the thorax irradiation and direct access operator positioning. In this case, on average, 80% of the scattered radiation is originating from the gaps beneath the lead glasses and 18% is backscattered from the head for both eyewear models and both eyes. The remaining part of the scattered radiation contributing to the total eye lens dose (1–16%) comes from photons penetrating the lead glasses. 3.1.2.  Effect of beam quality.  When different x-ray spectra were used, the difference to the dose reduction from the lead glasses was less than 5% for the range of energies and beam qualities that were tested. This indicates that the efficiency of the glasses is similar in typical clinical kVp/beam quality conditions. All following simulations were performed using the reference beam quality: 90 kV, HVL = 3.5 mm Al. 517

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Left eye

Contribution of scattered radiation to eye dose

(a) 100%

12%

90%

8% 24%

80% 70% 60%

62%

1%

64% 65%

50% 40% 30%

2%

91% 71%

3%

20% 10%

87%

1%

24%

30%

PA

LLAT

16%

0% RLAT

PA

L1

gap beneath glasses

LLAT

RLAT

L2

gap between L & R glass

backscattered from head

Right eye

(b) Contribution of scattered radiation to eye dose

100% 90% 80% 70% 60%

22%

34%

18%

63%

19% 30% 20%

62% 15%

13%

50% 40% 30% 20%

52%

5%

58%

61%

10%

52% 37%

30%

0% PA

LLAT

RLAT

PA

L1

gap beneath glasses

LLAT

RLAT

L2

gap between L & R glass

backscattered from head

Figure 5. Contribution to the eye lens dose of scattered radiation coming from the u­ nprotected parts of the head for the left eye (a) and the right eye (b) considering a ­thorax irradiation with the operator standing at 70 cm away from the x-ray field.

3.1.3.  Effect of thickness of lead glasses.  The study also investigated the effect of lead thickness while a thorax irradiation was simulated for PA, LLAT and RLAT beam projections and a 70 cm operator distance to the x-ray field. Simulations showed that there was no significant difference between 0.35 mm and 0.5 mm Pb thickness for the L1 type. Similarly, for the L2 type glasses, changing the lead thickness of both front and side protection glasses from 0.3 to 0.75 mm Pb did not induce any significant extra dose reduction to the eye lenses (changes within statistical errors). This result complies with the conclusion from Koukorava et al (2011a) stating that lead thicknesses larger than 0.5 mm did not improve the protection of the eye lenses significantly. 3.1.4.  Effect of beam projection.  In figures 6(a) and (b), the protection efficiency is given for the L1, L2 and L2′ eyewear models for different x-ray beam projections, including also biplanar configurations. The calculations were performed for a thorax irradiation with the operator at 70 cm and the reference thicknesses for the lead glasses (0.5 mm for L1 and 0.75 mm/0.3 mm for L2 and L2′). For all eyewear models, when RLAT projections are considered, the dose reduction is more important when compared to PA, LLAT and biplanar PA+LLAT configurations. This can be explained by the direction of the scattered radiation from the patient’s body. Indeed, in the case of a RLAT projection, more scattered radiation is striking the glasses from the front, when 518

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Left eye 1.00 0.80 0.60 0.40 0.20 RLA RLAT

CRAN CRAN20

P PA

LLA LLAT

RAO+LA AO+LAO

PA+LLA A+LLAT

L2

L2'

Right eye

(b) 1.00 0.80 0.60 0.40 0.20

L1

CRAN20 A

RLAT

LLAT L

PA

RAO+LAO +

PA+RLAT R

CRAN20 A L2

PA+LLAT L

RLAT R

LLAT L

PA

RAO+LAO +

PA+LLAT L

PA+RLAT R

RLAT R

CRAN20 A

PA

0.00 LLAT L

Hp(3) with/without lead glasses

PA+RLA A+RLAT

RLAT A

L1

CRAN20 CRAN

PA P

LLAT LLA

RAO+LA AO+LAO

PA+LLA A+LLAT

PA+RLA A+RLAT

RLAT RLA

CRAN20 CRAN

PA P

0.00 LLAT LLA

Hp(3) with/without le glasses hout lead

(a)

L2'

Figure 6. Protection efficiency of eyewear models L1, L2 and L2′ for different beam

projections. Calculations are performed for a thorax irradiation with the operator standing at 70 cm away from the x-ray field.

compared to PA and LLAT projections (cf table 1). At the same time, while not considering any lead glasses or other shields, the eye dose of the operator is 44% less when the RLAT projection is used compared to the LLAT one, according to the simulations performed within this study. 3.1.5.  Effect of operator position.  Table 2 presents the radiation protection efficiency of the different types of glasses considering different positions of the operator with respect to the radiation field. For a thorax examination, the operator is 40 cm away from the centre of the radiation field when considering a radial access route and 70 cm in the case of a femoral access. For a head irradiation the operator is at larger distances from the x-ray field for a femoral access simulation (70–110 cm). As the operator approaches the radiation field, the protection provided by the L1 glass model to the left eye is reduced while it increases for the right eye. This can be explained by the fact that when the operator approaches the x-ray field the gaps from beneath the glasses become more important for the left eye and less scattered radiation hits the glasses (from 87% to 60%) before reaching the left eye. At the same time a larger proportion of scattered radiation (from 12% to 51%) hits the glasses of the right eye, and therefore is stopped, before reaching the right eye (cf table 1). In general, the protection efficiency of models L2 and L2′ is not much affected by the distance of the operator to the field. For distances larger than 70 cm, the protection efficiency does not change further for both models, except for the right eye with model L2′, where the protection efficiency drops from 0.50 to 0.88 for larger distances. Moreover, the dose ratio with/without the glasses is the same for both eyes when the operator stands right next to the 519

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Table 2.  Ratios of Hp(3) values with/without lead glasses for different distances of the operator from the x-ray field (d), for thorax and head irradiation.

Thorax irradiation of patient

Head irradiation of patient

Type

Projection d (cm) Left eye Right eye

Type

Projection d (cm)

Left eye Right eye

L1

PA LLAT

L2

PA LLAT

L2′

PA LLAT

0 40 70 40 70

0.51 0.20 0.15 0.23 0.12

0.52 0.78 0.89 0.92 0.97

L1

PA

70 90 110

0.17 0.15 0.14

0.93 0.93 0.92

0 40 70 40 70

0.62 0.69 0.63 0.88 0.81

0.62 0.66 0.77 0.87 0.94

L2

PA

70 90 110

0.66 0.54 0.43

0.78 0.90 0.89

0 40 70 40 70

0.45 0.51 0.48 0.74 0.69

0.45 0.49 0.58 0.71 0.88

L2′

PA

70 90 110

0.49 0.41 0.34

0.50 0.79 0.88

x-ray field (0 cm). This result was confirmed using the cell flagging option which showed that about 80% of the total dose comes from beneath the glasses for both left and right eye lenses. These calculations were performed with the head of the operator facing forward (0° rotation). Additionally, the effect of the lead glasses was investigated if the operator’s head was rotated towards or away from the x-ray tube (table 3). Indeed, the operator’s head orientation depends on the position of the monitors in the x-ray room. It is clear from the results in table 3 that the rotation of the head can have an influence on the protection efficiency of the glasses, depending on the eyewear model, but also on the beam projection. The situation is also different for the left and right eyes. The protection efficiency of lead glasses (ratio with/without glasses) is generally increased when the operator is facing the x-ray tube compared to when he is facing away. However, better protection efficiency does not necessarily mean lower doses to the eyes. This is particularly true since the rotation of the head also directly influences the amount of scattered radiation reaching the eyes and therefore the dose value. Indeed, simulations show that left and right eye doses are generally lower when the operator faces away from the x-ray tube even though the efficiency of the glasses in that latter case is sometimes significantly reduced. Namely, for the L2 model and a LLAT projection, the protection efficiency is lower if the operator is turning his head away from (0.80 for the left eye and 0.73 for the right eye) compared to when he is facing the x-ray tube (0.25 and 0.24 for the left and right eyes respectively). Nonetheless, the eye doses (0.29 and 0.02 for the left and right eyes respectively) in the first case are lower than those of the second case (0.56 and 0.48 for the left and right eyes respectively); doses are normalized to the dose at the ID and, therefore, are unitless. Finally, even though the right eye is generally less exposed if no protection equipment is used, the situation may be different when lead glasses are worn. In the latter case the doses to the right eye are sometimes higher due to the lower protection efficiency of the lead glasses to the right eye. 3.1.6.  Effect of eyewear model 3.1.6.1.  Shape of the eyewear.  The effect of several configurations and irradiation condi-

tions on the protection efficiency of each of the three types of lead glasses (L1, L2 and L2′) 520

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Table 3. Ratios of Hp(3) values with/without lead glasses and the respective dose v­ alues when glasses are used for different rotations of the operator’s head, for thorax irradiation at a distance of 70 cm from the x-ray field.

Hp(3) with/without glasses

Hp(3)/dose at ID with lead glasses

Type

Projection

Head orientation

Left eye

Right eye

Left eye

Right eye

L1

PA

45° towards tube 0° facing forward 45° away from tube 45° towards tube 0° facing forward 45° away from tube

0.15 0.15 0.42 0.11 0.12 0.58

0.16 0.89 0.78 0.18 0.97 0.70

0.0027 0.0025 0.0033 0.26 0.24 0.22

0.0027 0.0089 0.0005 0.35 0.79 0.02

45° towards tube 0° facing forward 45° away from tube 45° towards tube 0° facing forward 45° away from tube

0.22 0.63 0.78 0.25 0.81 0.80

0.23 0.77 0.84 0.24 0.94 0.73

0.0039 0.011 0.006 0.56 1.61 0.29

0.0037 0.008 0.001 0.48 0.77 0.02

LLAT

L2

PA LLAT

was studied in the previous sections. The difference in protection efficiency for the three models is clear from figures 6(a)  and (b) for the left and right eyes, respectively. The L1 eyewear model protects more efficiently the left eye lens when compared to the L2 or the L2′ models. Indeed, the L1 type reduces the dose to left and right eye lenses by 87% and 24% respectively, while the L2 type reduces the dose by 44% and 36% (average values for all projections considered). Meanwhile, creating a tilt of 10° to the front lenses of the glasses (L2′ model) reduces the lower air gap between the eyes and the glasses and results in a more important dose reduction to the left and right eyes of 57% and 46% respectively (average values for all tested projections). To understand the differences in protection efficiency for each of the models, the results from section 3.1.1 (origin of scattered radiation) can be consulted. The efficiency for the right eye is particularly low for the L1 type glasses. On the one hand, table 1 indicates that, in most cases, a very small proportion of scattered radiation reaching the eyes will hit the lead glasses. Therefore, the largest part of scattered radiation will reach the eyes through the unprotected parts, mainly the air gaps beneath the lead glasses (cf figure 5(b)). On the other hand, the left eye is well protected since the largest part of the scattered radiation will hit the lead glasses and be stopped before reaching the eye. It should be mentioned, however, that the right eye is generally less exposed to x-rays than the left eye as the operator has the tube on his left side (about two times less when lead glasses are not used according to the simulations performed within this study). If the operator is aligned with the x-ray field, the dose levels, as well as the dose reduction coefficients of the different eyewear models, are similar for the left and right eyes. 3.1.6.2.  Size of the lenses and side protection.  The impact on protection efficiency of the size

of the lenses for the L1 model and that of the side protection for the L2 model were evaluated in the cases where the operator is facing forward (0°) and when he is rotated 45° facing away from the tube. In table 4 the results show that for the L1 model, the size of the lens (small: 5.5 cm and large: 7.5 cm) has hardly any effect on both eye doses and for both beam projections considered, regardless of the head orientation of the operator. It should be noted, however, that for the L1 model the eyes were well covered behind the Pb lenses for both the small and the large lenses. As for the L2 model the side protection size has an impact mostly on the left eye when the operator is facing away from the x-ray tube. In this particular case a small side pro521

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Table 4.  Ratios of Hp(3) values with/without lead glasses for different sizes of the lens and side protection.

Thorax irradiation; operator at 70 cm Type

Projection

Head orientation

Size

Left eye

Right eye

L1

PA

0° facing forward

small large small large small large small large

0.19 0.15 0.45 0.42 0.13 0.12 0.63 0.58

1.00 0.89 0.82 0.78 0.97 0.97 0.73 0.70

small large small large small large small large

0.65 0.63 0.98 0.78 0.82 0.81 0.99 0.80

0.80 0.77 0.88 0.84 0.94 0.94 0.81 0.73

45° away from tube LLAT

0° facing forward 45° away from tube

L2

PA

0° facing forward 45° away from tube

LLAT

0° facing forward 45° away from tube

tection (1.5 cm) leaves the left eye practically unprotected, while a large side protection (4 cm) increases the efficiency of the glasses by 20%, compared to the small side protection. Since there was no influence of the size of the side protection for the operator’s head facing forward (0° rotation) no further calculations were performed for the operator’s head rotated towards the x-ray tube. 3.1.6.3.  How the glasses fit on the face of the operator (size of air gaps).  Since the results of the cell flagging confirmed that a large amount of scattered radiation reaching the eyes comes from the gaps beneath the lead glasses (cf figure 5), modifications were made to the position of the L1 and L2 models in order to quantify the effect of the size of this air gap. This is equivalent to studying the protection efficiency of lead glasses based on how well they fit to the face of the operator. For each eyewear model three distances between the lead glasses and the operator’s head were simulated; for the L1 model air gaps of 0.5 cm (reference), 1 cm, 1.5 cm were considered, while for the L2 model these air gaps were 0.6 cm (glasses in contact with the face at the level of the nose representing the minimum possible gap for this specific shape and geometry), 1 cm (reference) and 1.5 cm gap at the level of the eyes (cf figures 2(f)–2(k)). The results in table 5 show that a small increase of the air gap between the glasses and the eye lens has a significant effect on the protection efficiency of the glasses. For the L1 model, when the gap is increased by 1 cm (from 0.5 cm to 1.5 cm), the efficiency of the glasses is reduced by about 38% for the left eye and the right eye becomes unprotected. For the L2 model, an increase of the gap by as little as 0.4 cm from the minimum possible gap (from 0.6 cm to 1 cm) reduces the efficiency of the glasses by 20% for the left eye and 27% for the right eye (average values for PA and LLAT projections). If the gap increases even more to 1.5 cm both eyes become practically unprotected. 3.2.  Protection efficiency of ceiling-suspended shields 3.2.1.  Effect on eye lens dose.  The effect of different ceiling-suspended screens on the eye lens doses was studied in the previously described irradiation configurations (different beam 522

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Table 5. Ratio of Hp(3) values with/without the lead glasses for different air gaps

­between the head and the lead glasses.

Thorax irradiation; operator at 70 cm Type

Projection

Air gap

Left eye

Right eye

L1

PA

0.5 cm (ref) 1 cm 1.5 cm 0.5 cm (ref) 1 cm 1.5 cm

0.15 0.27 0.47 0.12 0.32 0.55

0.89 0.98 0.99 0.97 0.98 1.00

0.6 cm 1 cm (ref) 1.5 cm 0.6 cm 1 cm (ref) 1.5 cm

0.41 0.63 0.84 0.62 0.81 0.88

0.41 0.77 0.96 0.75 0.94 0.98

LLAT L2

PA LLAT

1.0

Ratioo Hp (3) with/without shield

0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2

L R

70 cm (thorax) PA

110 cm (head) PA

70 cm (thorax) LLAT

A1+B2

B2

A2

A1

A1+B2

B2

A2

A1

A1+B2

B2

A2

A1

B2

B1

A2

A1

A2'

A2

A1'

A1

A2

0.0

A1

0.1

70 cm 70 cm 70 cm (thorax) (thorax) (thorax) PA+LLAT (Biplane) PA+RLAT (Biplane) LAO+RAO (Biplane)

Figure 7. Ratios of Hp(3) values with/without the use of different ceiling shields at

different configurations (arc type shield close to the patient A1, arc type shield 15 cm above the patient A2, rectangular shield close to the patient B1, rectangular shield on the side of the operator B2, arc type shield close to the x-ray field and close to the patient A1′, 15 cm above the patient A2′ for head irradiation). The first and second bars of each category represent the left (L) and right (R) eyes respectively.

projections, operator distances from x-ray field, etc). The results are presented in figure 7. For all the simulated irradiation conditions (25 in total), the dose reduction due to the shields was, on average, 55% for the left eye and 58% for the right eye. In general, when the A1 shield is compared against the A2 shield, the protection efficiency is of the same order of magnitude, except for the LAO+RAO biplanar setup where the A1 shield is about 25% more efficient for both eyes. However, one should notice the difference between A1 and A1′ cases. Namely, if the shield is positioned close to the operator (A1) instead of being close to the irradiated part of the body (A1′), the ‘shadow’ created from the screen is smaller and a slight movement of the operator would leave him unprotected against scattered radiation. Moreover, figure 7 523

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Table 6.  Ratios of Hp(10) values with/without a ceiling shield at different positions.

The cases in bold indicate the configurations that provide optimal protection.

Configurations

Collar Collar Collar Chest Chest Chest Waist Waist Waist L M R L M R L M R

A1 A2 PA Head A1 A1′ A2 A2′ LLAT Thorax A1 A2 B1 B2 PA+LLAT Thorax A1 A2 B2 A1+B2 A2+B2 PA+RLAT Thorax A1 A2 B2 A1+B2 A2+B2 LAO+RAO Thorax A1 A2 B2 A1+B2 A2+B2 Mean

0.41 0.64 0.95 0.16 0.97 0.96 0.88 0.89 0.59 0.09 0.90 0.95 0.08 0.01 0.04 0.09 0.18 0.95 0.03 0.13 0.20 0.66 1 0.07 0.66 0.50

PA

Thorax

0.26 0.59 0.93 0.18 0.89 0.95 0.86 0.90 0.32 0.17 0.87 0.94 0.17 0.06 0.11 0.04 0.56 0.98 0.04 0.54 0.14 0.80 0.95 0.07 0.76 0.52

0.18 0.64 0.84 0.21 0.93 0.96 0.85 0.91 0.15 0.27 0.81 0.95 0.27 0.14 0.24 0.05 0.93 1 0.05 0.87 0.11 0.86 1 0.15 0.88 0.57

0.42 0.86 0.85 0.43 0.93 0.89 0.81 0.96 0.57 0.27 0.79 0.97 0.27 0.08 0.24 0.08 0.89 0.94 0.08 0.85 0.34 0.87 0.93 0.28 0.87 0.62

0.24 0.91 0.88 0.54 0.90 0.93 0.58 0.93 0.22 0.52 0.71 0.94 0.53 0.14 0.50 0.11 0.91 0.95 0.06 0.89 0.22 0.94 0.95 0.22 0.94 0.63

0.25 0.94 0.99 0.60 0.91 0.96 0.67 0.95 0.17 0.51 0.60 0.98 0.50 0.20 0.49 0.10 0.93 0.97 0.10 0.92 0.22 0.93 0.95 0.22 0.94 0.64

0.66 0.74 0.61 0.57 0.62 0.99 0.97 0.96 0.97 0.98 0.97 1 1 0.99 1 0.47 0.86 0.82 0.42 0.70 0.86 0.90 0.92 0.87 0.90 0.83

0.58 0.69 0.55 0.47 0.54 0.55 0.94 0.95 0.97 1 0.96 0.99 0.98 0.96 0.98 0.46 0.77 0.84 0.49 0.70 0.81 0.90 0.94 0.81 0.87 0.79

0.62 0.73 0.48 0.39 0.49 0.58 0.96 0.96 0.92 0.97 0.96 1 1 1 1 0.54 0.91 0.89 0.44 0.74 0.65 0.88 0.91 0.67 0.85 0.78

shows that for the A1′ and A2′ configurations (shield close to x-ray field), a large gap (of about 15 cm) between the screen and the patient allows a significant amount of scattered radiation to reach the operator compared to when the shield is close to the patient’s body. When the operator stands at the side of the tube for a lateral projection (LLAT here), a shield positioned closer to his side (B2) and not above the patient (B1) is more efficient. This does not hold for the RLAT projection (tube at the opposite side of the operator) due to the direction of the scattered radiation. Finally, a combination of two shields (A1+B2), one above the patient and one on the side of the operator, reduces the dose to the eye lenses by more than 90% when biplanar configurations are used (cf figure 7). 3.2.2.  Effect on whole body dose.  The study also focused on estimating the efficiency of the different shields on WB doses, expressed in terms of Hp(10), recorded at the collar, chest and waist level above the lead apron. Table 6 documents the simulation results for WB doses while using the different ceiling shields and tube projections (25 simulations in total). The results have shown that the protection efficiency of such screens varies for different levels on the trunk. For example, in a LLAT projection, a B2 shield is very efficient to protect the collar region while its efficiency decreases for the chest region and becomes very low for the waist region. On average, the doses measured at collar, chest and waist levels are reduced by 47%, 37% and 20% respectively, when a ceiling-suspended shield is used. For the same irradiation conditions, the average dose reduction to both eyes was 56%, a value close to that found for the dosemeters positioned at the level of the collar. This result shows that the attenuation of 524

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scattered radiation under these conditions is roughly equivalent at the eye and collar levels. Previous findings have also shown that the eye lens dose correlates best with the dose at the level of the collar; however, great variations were also observed and such correlations should be considered with caution (Farah et al 2013). Finally, the position of the ceiling shields should be adapted based on tube configuration and operator’s positioning. The configurations that provide optimal protection are highlighted in table 6. 3.3.  Influence of the ID position

Finally, one last parameter which can vary during a fluoroscopically guided procedure is the position of the ID. Indeed, the latter may stop a significant amount of scattered radiation coming from the patient and could therefore also influence the dose to the eyes. Four different distances between the ID and the patient were thus considered (10 cm, 20 cm, 30 cm and 40 cm) and eye doses were calculated for a specific geometry (PA projection, thorax irradiation, femoral access). This was done in the absence of any other protective equipment. Doses are normalised to the dose at the entrance of the ID to account for the increase of exposure parameters that occurs on fluoroscopic systems with AEC when the distance between the ID and the x-ray tube increases. Possible increase in kV would be small and have little effect on eye lens dose, especially in the case of PA and small angled anterior oblique projections; therefore, it is not taken into account in the results. For all simulations, the same beam quality (90 kVp/3 mm Al) was used. To determine the influence of ID position on eye lens dose, ­calculations were normalised to the eye lens dose obtained for the ID–patient distance of 10 cm configuration. The results presented in table 7 show that increasing the gap between the ID and the patient from 10 cm to 30 cm would increase the dose to both eyes by a factor of 4 for this specific geometry. 4. Discussion Simulations showed that the shape of lead glasses, the position and head orientation of the operator relative to the patient and to the x-ray tube, as well as the beam projections play an important role in the radiation protection efficiency of lead glasses. Less important were the effects of beam quality, lead thickness and size of the side protection. In general, the average protection efficiency for the models considered in this study, taking into account all the investigated parameters, is as follows: - L1 model: 0.26 with a standard deviation of 63% for the left eye       0.79 with a standard deviation of 30% for the right eye - L2 model: 0.59 with a standard deviation of 39% for the left eye       0.68 with a standard deviation of 39% for the right eye Measurements performed on anthropomorphic phantoms using different eyewear models (Geber et al 2011, Sturchio et al 2013) have also demonstrated significant differences in their efficiency in protecting the eyes. Sturchio et al (2013) tested three models of eyewear and found a dose reduction ranging from 44% to 80% to the eye that is closer to the tube. This result is very similar to the range found in the present study for similar irradiation conditions (34–85% for the left eye, PA projection, femoral access and operator 70 cm from the isocentre). In this study, more irradiation conditions are considered, which has an influence on the results. For example, the respective range when all tested beam projections are considered was found to be 14%–90% for the left eye. Geber et al (2011) tested eight models of eyewear for anterior oblique beam projections (the angle is not specified) and found a dose reduction that varied between 14% and 78% for the left eye lens and 525

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Table 7.  Hp(3)/dose to ID for three distances of the ID from the patient, normalized to

the distance of 10 cm (reference) for thorax irradiation, PA projection and the operator at the patient’s femur.

Distance of ID from patient 20 cm 25 cm 30 cm

[Hp(3)/dose at ID]d/ [Hp(3)/dose at ID]10] Left ­eye

Right eye

2.6 3.3 4.0

2.5 3.2 3.9

2–12% for the right eye lens. This also joins the observation of this paper where the left eye was found to be better protected than the right eye when lead glasses are used. The efficiency of the glasses was found to increase when the operator is facing the x-ray tube since a larger amount of the scattered radiation coming from the patient is striking the glasses from the front and a lower proportion is slipping through the gaps. In the present study, also the size of the side protection was investigated as a function of operator’s head orientation and we found that the side protection size has only an effect on eye lens dose when the operator is looking away from the x-ray tube. Both results comply with the findings of previous studies (Sturchio et al 2013). At the same time, when considering the head orientation of the operator and, therefore, the position of the diagnostic monitors, the doses were found to be generally lower for both left and right eyes when the operator is facing away from the x-ray tube, with and without glasses, although the efficiency of the glasses, especially for the left eye, is sometimes significantly reduced. It is also important to note that although the protection efficiency of lead glasses can vary a lot between the left and right eyes in different exposure conditions, one should also bear in mind that the actual dose received by the left and right eyes is very different. In most cases, the left eye is more exposed if no protection equipment is used, but when lead glasses are worn, the left eye is also better protected. This might result in higher doses to the right eye compared to the left eye in the case where lead glasses are worn. The ceiling-suspended screens equally protect both eyes in most of the cases and provide also shielding to the upper body of the operator. However, the optimal positioning of such screens should be adapted based on the configuration especially with tube projection and access route (i.e. operator’s positioning). In general, it is recommended to place the screens close to the patient (in the vertical direction) and close to the irradiated part of the body (in the horizontal direction), to cut off a larger amount of scattered radiation and create a larger ‘shadow’ in order to protect also other people who may be circulating in the operating room. For large angled LAO projections (e.g. LLAT) moving the ceiling shield towards the side of the operator (i.e. x-ray tube side) is more appropriate, while for biplanar configurations involving LLAT projections the use of a second shield should be considered. Moreover, calculations showed that not only the shape and position of a ceiling shield influence its protection efficiency, but also the protection provided has a different influence on the reading of the WB dosemeter depending on where the dosemeter is positioned (head and neck, torso or abdominal region). This is critical information to be considered with caution when WB doses are used to estimate the eye lens doses (Farah et al 2013). Finally, positioning the ID as close as possible to the patient was found to sensitively reduce operator’s exposure to scattered radiation. In operating theatres where mobile C-arm systems are used most often without any shield protection, a correct position of the ID could help in reducing the operator exposure. An increase in the distance between the ID and the patient from 10 cm to 20 cm, for a PA projection, was associated with an increase in the eye lens doses by a factor of 2.5. This is also in agreement with the literature since a twofold 526

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increase in lens dose was found by Thornton et al (2010) from measurements performed with an anthropomorphic phantom in similar conditions. In addition to the increased dose to the operator, one should keep in mind that, in practice, when the ID is moved away from the source, the irradiation parameters increase resulting also in higher patient dose. 5. Conclusions The study highlighted that the protection of operators’ eyes and more generally their whole body strongly depends not only on the types of personal and collective radiation protection equipment that are used but also on how they are used and on the working procedure. It is important for professionals working in the field of IR or IC to be trained to use the available protective devices correctly. Regarding the protection of the eye lens, medical professionals are advised to select their protective eyewear individually, based on how well they fit their face. It is clear from this study that not all lead glasses provide the same protection to the eye lens. In particular, physicians who need to stand close to the patient (e.g. interventions using direct access such as pacemaker implantations, nephrostomies, etc) are strongly advised to wear glasses with the minimum possible gaps between the face and the eyewear, since a large amount of scattered radiation reaches both eyes through these gaps. The right eye was found to be less protected than the left eye with the use of different lead glasses. Moreover, the head orientation of the operator was found to have an impact on the efficiency of the glasses but also on eye doses. It is suggested that the diagnostic monitors are positioned away from the x-ray field, since the eye doses of the operator were found to be lower for this configuration. However, the protection efficiency of the glasses was also found to be lower in that case. Therefore, ceiling-suspended screens should be used whenever possible additionally to the lead glasses since they can reduce the dose equally to both eyes and also protect very efficiently the upper body of the operator (50–80%) as well as other people present in the operating room (technicians, nurses, etc). A ceiling shield is more effective when positioned close to the patient’s skin and close to the x-ray field. A shield slightly shifted towards the side of the operator is more efficient for LLAT projections and even a second shield on the side should be considered for biplanar configurations. A combination of ceiling shield and lead glasses can minimise the dose to both eyes to the lowest possible levels. Finally, the shielding that the ID provides should be exploited in routine practice. Placing the detector as close as possible to the patient, especially when PA and small angled anterior oblique projections are used, can significantly reduce the exposure of the staff and protect the patient at the same time. Communicating the likelihood of eye lens opacities, thus sensitizing the staff working in IR/IC departments to radiation protection issues, together with proper training, are the key factors for minimising the risks associated with the use of ionising radiation. References Carinou E et al 2011 Recommendations to reduce extremity and eye lens doses in interventional radiology and cardiology Radiat. Meas. 46 1324–29 Chodick G et al 2008 Risk of cataract after exposure to low doses of ionizing radiation: A 20-year prospective cohort study among US radiologic technologists Am. J. Epidemiol. 168 620–31 Ciraj-Bjelac O, Rehani M M, Sim K H, Liew H B, Vano E and Kleiman N J 2010 Risk for radiationinduced cataract for staff in interventional cardiology: Is there reason for concern? Catheter Cardiovasc. Interv. 76 826–34 Dauer L T, Thornton R H, Solomon S B and St Germain J 2010 Unprotected operator eye lens doses in oncologic interventional radiology are clinically significant: estimation from patient kerma-areaproduct data J. Vasc. Interv. Radiol. 21 1859–61 527

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