Radiation Protection Dosimetry (2015), Vol. 165, No. 1–4, pp. 289 –293 Advance Access publication 24 March 2015

doi:10.1093/rpd/ncv051

EYE LENS DOSE IN INTERVENTIONAL CARDIOLOGY S. Principi1,*, C. Delgado Soler2, M. Ginjaume1, M. Beltran Vilagrasa2, J. J. Rovira Escutia2 and M. A. Duch1 1 Institut de Te`cniques Energe`tiques, Universitat Polite`cnica de Catalunya, Barcelona, Spain 2 Physics and Radiation Protection Department, Hospital Universitari Vall d’Hebron, Barcelona, Spain *Corresponding author: [email protected]

INTRODUCTION (1 – 3)

on radio-induced cataEpidemiological studies ract formation have highlighted the fact that the actual dose limit for the eye lens may be too high, and that the eye lens may also be a more radiosensitive tissue than previously considered. Based on this evidence, the ICRP has recently recommended reducing the limit to the eye lens from 150 to 20 mSv y21, averaged over a period of 5 y, with no year exceeding 50 mSv(4). The main consequences of this limit reduction are the operational implications for workers exposed to non-homogeneous ionising radiation fields. Interventional cardiology and radiology (IC/IR) are two of the fields most affected by the decrease of the limit. Indeed, IC procedures require the physician to be in close proximity to the patient, who represents the main source of scattered radiation. The main problem of finding a low dose-lens damage relation through these studies is the very late manifestation of the disease. To study a correlation between cataract or opacity formation and very low doses, a long follow-up period is needed. In addition, the incidence of non-radiation-induced cataracts also increases with age. A recent investigation(1) shows, however, that radio-induced cataract is typically developed in the subcapsular region of the eye, a completely different region from where age-induced opacities are found. A wide number of parameters can influence the dose to eye lens, such as the use of radiation protection tools, beam features, beam projections and the interventional procedures performed(5).

The main goal of this study is to estimate the annual dose to the eye lens on IC workers, and to determine whether eye lens dose monitoring or/and additional radiological protection measures for a staff are required. Furthermore, a study on the correlation between the personal dose equivalent, Hp(3), and other quantities, such as Hp(10), Hp(0.07) or dose area product (DAP), has also been performed. MATERIALS AND METHODS For the assessment of the operational quantities of interest, two dosemeter holders were investigated: whole-body dosemeters for measurement of Hp(10) and Hp(0.07) and two different casings for estimating Hp(3), a polyethylene (PE) bag and the EYE-D dosemeter by Radcard (http://www.radcard.pl/). LiF: Mg,Cu,P thermoluminescent detectors, type thermoluminescent dosemeter (TLD)-2000C, with a diameter of 4.5 mm, a thickness of 0.8 mm and a corresponding density of 2.65 g cm23, were used. Dosemeters were calibrated with ISO narrow spectra(6) and RQR qualities(7), because the energy range and the less filtered radiation that characterise IC/IR beams (20–150 keV) are closer to the RQR energy domain(8). The newly suggested cylinder phantom was used for Hp(3) set-up calibration(9), as it better approximates the shape of a human head than the ISO slab phantom. Calibration and read-out details are described in Sanchez et al.(10) and Ginjaume et al.(11). Eye lens doses are not measured in routine practice and there are no commonly available dosemeters. The EYE-D dosemeter is a prototype optimised to respond

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The ICRP has recently recommended reducing the occupational exposure dose limit for the lens of the eye to 20 mSv y21, averaged over a period of 5 y, with no year exceeding 50 mSv, instead of the current 150 mSv y21. This reduction will have important implications for interventional cardiology and radiology (IC/IR) personnel. In this work, lens dose received by a staff working in IC is studied in order to determine whether eye lens dose monitoring or/and additional radiological protection measures are required. Eye lens dose exposure was monitored in 10 physicians and 6 nurses. The major IC procedures performed were coronary angiography and percutaneous transluminal coronary angioplasty. The personnel were provided with two thermoluminescent dosemeters (TLDs): one calibrated in terms of Hp(3) located close to the left ear of the operator and a whole-body dosemeter calibrated in terms of Hp(10) and Hp(0.07) positioned on the lead apron. The estimated annual eye lens dose for physicians ranged between 8 and 60 mSv, for a workload of 200 procedures y21. Lower doses were collected for nurses, with estimated annual Hp(3) between 2 and 4 mSv y21. It was observed that for nurses the Hp(0.07) measurement on the lead apron is a good estimate of eye lens dose. This is not the case for physicians, where the influence of both the position and use of protective devices such as the ceiling shield is very important and produces large differences among doses both at the eyes and on the thorax. For physicians, a good correlation between Hp(3) and dose area product is shown.

S. PRINCIPI ET AL.

three different operating rooms with three Philips Allura X-ray systems: one FD10, one FD10/10 and one Clarity FD10. The measurement protocol was divided into two phases. During the first period, eye lens dose exposure was monitored for nine physicians and six nurses. Follow-up lasted for 2 weeks. Dosemeters were changed after each procedure for the physicians, whereas nurses wore the same dosemeter during all the monitoring period. The second follow-up period lasted 7 weeks and included three physicians and one nurse. Dosemeters were changed weekly, both for physicians and nurses. The main IC procedures performed were coronary angiography and percutaneous transluminal coronary angioplasty. The mean workload for physicians was 9 procedures week21 with a mean measured DAP of 1100 Gy cm2 week21. However, there was large variability in workload and measured DAP from week to week: the number of procedures per week ranged between 0 and 21 while weekly DAP was in the region of 0–3290 Gy cm2 (s.d. 19 %). As mentioned earlier, only one physician has his own lead glasses (Figure 1), whereas all physicians used both lead apron and thyroid collar. Only one nurse wore the thyroid protection. In relation to the room radiation protection tool, a table shield was always employed while a ceilingsuspended screen was used 78 % of the time because, depending on the procedures, it disturbs the physicians’ work. RESULTS AND DISCUSSION First follow-up period

Figure 1. Dosemeters located on the external left side and behind the lead lens of the glasses.

Figure 2. Dosemeter located on the left side of the cap.

Table 1 summarises the mean measured Hp(3) per procedure (,Hp(3)/proc.) and the corresponding standard deviation (1 s.d.) for the nine physicians during the first follow-up period. The estimated annual eye lens dose is then obtained by multiplying ,Hp(3)/proc. by the number of procedures performed in 1 y. Data show that four physicians out of nine exceeded the new recommended limit of 20 mSv y21. ,Hp(3)/proc. ranges from 42 to 251 mSv proc21, while the estimated annual doses range between 8 and 61 mSv y21. Large variability of the measured Hp(3) per procedure is observed. The standard deviation of Hp(3)/proc is of the order of 80 % even for each individual physician. This variability is mainly due to the high DAP values recorded in some procedures, where a long fluoroscopy time is required, and to the inappropriate use of shielding. For instance, in paediatric interventions (physician 3), the ceiling-suspended screen is often disregarded because it is uncomfortable for the correct work. Two values of Hp(3)—equal to 780 and 540 mSv corresponding to high DAP procedures of 260 and 400 Gy cm2, respectively—were removed to derive the annual dose, according to the Stem-and-Leaf Diagram performed with the SPSS program(12). If outlier values

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in terms of Hp(3) and is now on the market; however, it does have several practical difficulties for use in routine monitoring. The need to find a compromise between placing the eye lens dosemeter as near as possible to the most exposed eye and avoiding discomfort to the physician has led to the consideration of defining a simpler casing, calibrated to respond in terms of Hp(3). For the measurement campaign, a PE bag holder was used instead of the EYE-D, because it was preferred by the monitored physicians. The bag is made of a 0.11-mm-thick PE plastic, with a density of 0.98 g cm23, and contains two TLDs. The eye lens dosemeters were located on the external left side of normal glasses (Figure 1). When goggles were not worn by the worker, the dosemeter was stuck on the left side of the cap (Figure 2). In one case, a physician had his own lead glasses and so the dosemeters were located both on the external left side of the glasses and on the inner part, just behind the lead glass (Figure 1). The left side was chosen because it is often the closest to the X-ray tube and the dose measured is a good estimate of the maximum eye dose. An additional whole-body dosemeter for the estimation of the quantities Hp(0.07) and Hp(10) was supplied to the staff and was located on the lead apron, on the left side of the thorax. The measurements were performed in the Hemodynamic Department at the Vall d’Hebron Hospital in Barcelona, Spain. The department is provided with

EYE LENS DOSE IN INTERVENTIONAL CARDIOLOGY Table 1. Mean measured Hp(3) per procedure + 1 s.d., number of procedures per year and estimated annual dose for physicians. No. proc y21

Hp(3) y21 in mSv

164+129 42+ 39 218+163 62+45 45+42 49+46 65+53 251+187 130+102

369 303 149 253 182 253 325 77 385

61 13 32 16 8 12 21 19 50

Phys_3 Phys_9 Phys_10a Nurse 6

Nurse 1 Nurse 2 Nurse 3 Nurse 4 Nurse 5 Nurse 6

No. proc y21

Hp(3) y21 in mSv

11 18 14 22 13 24

209 193 171 105 176 171

2 3 2 2 2 4

No. proc y21

Hp(3) y21 in mSv

171+83 65+44 56+18 13+5

149 385 191 171

25 25 11 2

a

Phys_10 is wearing lead goggles, and Hp(3) is estimated using the dosemeter in the internal part.

Table 2. Mean measured Hp(3) per procedure, number of procedures per year and estimated annual dose for nurses. ,Hp(3)/proc. in mSv

,Hp(3)/proc.+1 s.d. in mSv

were included, the estimated annual dose would increase up to 75 mSv for physician 1 and up to 113 mSv for physician 9. This highlights the fact that a larger period of monitoring is needed for a more reliable estimate of the annual eye lens dose. Table 2 presents the estimated annual eye lens dose for nurses. In this case, nobody exceeds the recommended 20 mSv y21 and the range of variability among the different monitored nurses is small. Second follow-up period The attenuation factor due to the use of lead goggles has been estimated for 5 weeks. The mean ratio between Hp(3) measured over the external left earpiece and behind the glass of the goggles is 3.5 and ranges from 2.5 to 4.8. In Table 3, the mean and standard deviation of Hp(3) per procedure, number of procedures per year and estimated annual Hp(3) are listed for the second follow-up period. In this case, two physicians out of three exceed the annual limit. The mean Hp(3) per procedure for Phys. 3 and 9 was lower than in the first follow-up. The longer the measuring period, the more reliable the estimation of annual Hp(3). Table 3 highlights the fact that the standard deviation associated

with Hp(3) per procedure for a weekly monitoring period is reduced to 45 %, compared with 80 % for single procedure monitoring. Considering that in most cases estimated annual doses for physicians are higher than 15 mSv, regular monitoring should be introduced. The square of the Pearson coefficient is used to measure the strength of the linear relationship between Hp(3) and Hp(0.07) measured on the lead apron and the DAP, both for nurses and for physicians when they operate as a first physician, which means that it is the physician who stands closest to the X-ray tube. Figure 3a and b shows that the correlation between Hp(3) and Hp(0.07) is quite poor for physicians at the first position (R 2 ¼ 0.4), whereas it is better for nurses (R 2 ¼ 0.8). The ratio between Hp(0.07) and Hp(3) is found to be close to 1 for nurses. Therefore, Hp(0.07) measured above the apron, on the left side of the thorax, can be considered a good estimator of the dose to the eye lens for nurses, but not for physicians. Correlation with the DAP was also analysed (Figure 4a and b). In this case, the correlation is higher and the spread of data is smaller for physicians at the first position (R 2 ¼ 0.6 and s.d. ¼ 2.7 %, respectively) rather than for nurses (R 2 ¼ 0.5 and s.d. ¼ 20 %). A review of eye lens dose data reported in the literature shows a large variability(13).This is in agreement with the rather large range obtained in this study. A mean value of Hp(3) per procedure was found for cardiologists of 0.17 mSv with a range of 0.009–0.78 mSv, which follows the range of values obtained from the ORAMED study: a mean value of 0.057 mSv proc21 and a range of 0.004–0.82 mSv proc21. With regard to the Hp(3) per unit DAP, our values, 1.81 (0.52 – 6.08) mSv Gy cm22, are higher than the mean values from the ORAMED campaign(8), 1.0 mSv Gy cm22. This could highlight the fact that the use of protection is not optimised. In particular, for paediatric interventions, for the same amount of DAP, high Hp(3) are recorded, due to the proximity of the physician to the tube because of the small size of the patient, the preferred use of biplane system to monoplane

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Phys. 1 Phys. 2 Phys. 3 Phys. 4 Phys. 5 Phys. 6 Phys. 7 Phys. 8 Phys. 9

,Hp(3)/proc.+1 s.d. in mSv

Table 3. Mean measured Hp(3) per procedure + 1 s.d., number of procedures per year and estimated annual dose values for the second follow-up period.

S. PRINCIPI ET AL.

Figure 4. (a) Correlation between DAP and Hp(3) for physician at the first position. (b) Correlation between DAP and Hp(3) for nurses.

system and the general lack of a ceiling-suspended screen. CONCLUSIONS This study shows that the new ICRP recommended limit of 20 mSv y21 for the lens of the eyes can be easily surpassed for IC physicians and implies that regular monitoring should be done for these workers. This means that accredited personal dosimetry laboratories should supply personal dosemeters calibrated to measure Hp(3), which is not the usual practice. A large variability of Hp(3) values are observed, even for the same physician, probably because the use of radiation protection tools in the routine practice is not always appropriate. The ceiling-suspended screen provides good protection but, in practice, it is not always well placed to protect the eyes. The use of lead glasses reduces the dose to the eye lens by an additional factor of 3.5, but personal prescription glasses for each physician are not usually provided, although one monitored physician was wearing them. Nurses receive a dose to the eye lens of 3 mSv y21, which is largely below the limit

and no additional monitoring is needed for this collective. Hp(0.07) has been found to be a good estimator of Hp(3) for nurses, but not for cardiologists. In this case, the DAP may be a better indicator of the dose to the eye lens. In summary, this study highlights the need to regularly monitor eye lens doses for interventional cardiologists. Additionally, the regular use of radiation protection tools should be optimised. Both information and training campaign for workers in IC/IR, aimed at increasing risk awareness among staff and at improving the use of radiation protection tools, would be helpful to reduce the dose in the lens of the eye. FUNDING This work was supported by the Consejo de Seguridad Nuclear (Nuclear Safety Council). REFERENCES

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Figure 3. (a) Correlation between Hp(0.07) and Hp(3) for physicians at the first position. (b) Correlation between Hp(0.07) and Hp(3) for nurses.

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Eye lens dose in interventional cardiology.

The ICRP has recently recommended reducing the occupational exposure dose limit for the lens of the eye to 20 mSv y(-1), averaged over a period of 5 y...
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