Radiation Protection Dosimetry Advance Access published October 14, 2014 Radiation Protection Dosimetry (2014), pp. 1–5
doi:10.1093/rpd/ncu315
APPLICATION OF THE ELDO APPROACH TO ASSESS CUMULATIVE EYE LENS DOSES FOR INTERVENTIONAL CARDIOLOGISTS
*Corresponding author: Email: [email protected] In preparation of a large European epidemiological study on the relation between eye lens dose and the occurrence of lens opacities, the European ELDO project focused on the development of practical methods to estimate retrospectively cumulative eye lens dose for interventional medical professionals exposed to radiation. The present paper applies one of the ELDO approaches, correlating eye lens dose to whole-body doses, to assess cumulative eye lens dose for 14 different Finnish interventional cardiologists for whom annual whole-body dose records were available for their entire working period. The estimated cumulative left and right eye lens dose ranged from 8 to 264 mSv and 6 to 225 mSv, respectively. In addition, calculations showed annual eye lens doses sometimes exceeding the new ICRP annual limit of 20 mSv. The work also highlights the large uncertainties associated with the application of such an approach proving the need for dedicated dosimetry systems in the routine monitoring of the eye lens dose.
INTRODUCTION The recurrent occupational exposure to radiation of the eye lens has become a real concern for interventional medical professionals since it may lead to the development of lens opacities(1). Recent epidemiological studies have shown that lens opacities may appear for doses lower than previously considered(2 – 3). Measurements of eye lens dose, performed on physicians during interventional procedures, and several studies assessing operator’s eye lens doses from patient dose indicators, have shown that the new annual limit of 20 mSv recommended by the ICRP(4) can be exceeded in numerous cases(5 – 9). In preparation of a large European epidemiological study on the relation between eye lens dose and the occurrence of lens opacities, the European ELDO project focused on the development of practical methods to estimate cumulative eye lens dose for interventional radiologists and cardiologists. Two approaches(10) were introduced within ELDO to estimate eye lens dose starting from available data. In the first approach, a mean eye lens dose for specific procedures—recently established within the European ORAMED(8) project—is used in combination with collected information regarding workload, X-ray system and radiation protection devices used. This
method accounts for the evolution of X-ray systems and procedures over the last 50 y and its influence on eye lens dose to the medical worker. In the second approach, eye lens dose is estimated directly from whole-body dose equivalents, Hp(10), measured above the lead apron. The present paper applies the second ELDO approach to assess cumulative eye lens dose for 14 different Finnish interventional cardiologists for whom annual whole-body doses, recorded above the lead apron, were available for their entire working period. The work also calculates annual eye lens doses and compares those with the new ICRP annual limit (4). Finally, uncertainties associated with the use of such an approach are calculated to investigate its viability for routine monitoring purposes as well as for retrospective epidemiological studies. MATERIALS AND METHODS Eye lens dose correlation to whole-body dose The ELDO project included a large phantom-based measurement campaign carried out in typical interventional settings considering different tube projections beam energies, operator positions and access routes and using both mono-tube and biplane X-ray
# The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
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J. Farah1, L. Struelens2, A. Auvinen3, S. Jacob1, C. Koukorava4, M. Schnelzer5, F. Vanhavere2 and I. Clairand1 1 Laboratoire de Dosime´trie des Rayonnements Ionisants, Institut de Radioprotection et de Suˆrete´ Nucle´aire (IRSN) – PRP-HOM/SDE – BP17, Fontenay-aux-Roses Cedex 92262, France 2 Department of Radiation Protection Dosimetry and Calibration, Belgian Nuclear Research Centre, Boeretang 200, Mol BE-2400, Belgium 3 Research and Environmental Surveillance Department, Radiation and Nuclear Safety Authority, PO BOX 14, Helsinki 00881, Finland 4 Division of Licensing and Inspections, Greek Atomic Energy Commission, PO Box 60092, Ag. Paraskevi, Athens 15310, Greece 5 Radiation Epidemiology Unit, Federal Office for Radiation Protection, Ingolsta¨dter Landstraße 1, Oberschleißheim 85764, Germany
J. FARAH ET AL.
Accounting for radiation protection equipment Within the ELDO project, for practical reasons, all measurements excluded the use of radiation protection equipment. Thus, in addition within this same project, Monte Carlo simulations were considered to provide the necessary correction coefficients that account for the impact of personal and collective radiation protection equipment on eye and whole-body Table 1. Ratio of left/right eye lens dose and on phantom chest left Hp(10) value, specific per type of procedure: (a) unknown class (N.A.), (b) CA/PTCA and RFA and (c) PM and ICD. Procedure type
N.A. CA/PTCA and RFA PM and ICD
Ratio eye lens dose/ Hp(10)chest,left
Uncertainty (%)
Left eye
Right eye
Left eye
Right eye
0.87 0.69 0.70
0.74 0.52 0.59
87 52 23
85 62 33
Values taken from Farah et al.(11) Uncertainty coefficients (k ¼ 1) are given as the spread of the ratio of eye dose/Hp(10) as a function of beam projection, operator position, etc.
doses(12). Table 2 provides the results of the profound simulation study in which the radiation protection efficiency of different eyewear models was determined considering again various clinical interventional conditions. As the protection efficiency can be very different depending on the shape of the lead glasses, a correction coefficient is given separately for two basic models representing typical rounded and squared glasses. A distinct coefficient is also given for cases where the glass model is unknown; this coefficient represents the average protection obtained with MC simulation considering altogether both eyewear models and all working conditions. The spread on all simulations (.100 scenarios considered) of the average simulated protection coefficients is also documented in Table 2. One should again note that the protection coefficients, obtained from MC simulations, do not include uncertainty due to changes in operator position or beam quality throughout the intervention. Data of Hp(10) records and work conditions To determine cumulative eye lens doses using this ELDO approach, whole-body dose equivalents measured above the lead apron are required for the entire working period. Table 3 documents the data available for 14 different Finnish interventional cardiologists including the number of years in practice, annual workload, type of procedures typically done and the use of radiation protection equipment. None of the interviewed cardiologists indicated ever using ceilingsuspended screens. Only few operators reported the use of lead glasses, without any specification on the model, as of a certain moment in their career. One should note, finally, that the recorded cumulative Hp(10) values may not reflect the exact exposure to radiation as the systematic wearing of whole-body dosemeters cannot be guaranteed. Table 2. Protection coefficient, ratio of Hp(3) doses with/ without the lead glasses, specific for unknown eyewear model, rounded eye glasses and squared models. Eyewear model
N.A. Rounded Squared
Protection coefficient
Uncertainty (%)
Left eye
Right eye
Left eye
Right eye
0.42 0.26 0.60
0.72 0.79 0.69
62 63 39
37 30 39
Values taken from Koukorava et al.(12) Uncertainty coefficients (k ¼ 1) are given as the spread of the ratio of protection coefficients as a function of beam projection, operator position, etc.
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systems(11). Measurements showed that eye lens dose correlates best with Hp(10) registered on the left side of the phantom at the level of the collar. This correlation, however, implicates high uncertainties, with a Standard Deviation of 41 % on the average ratio between eye lens dose and Hp(10). In addition, since such a wearing position of the dosemeter is not typical, the correlation to the whole-body dose measured on the left side of the chest was also considered. Table 1 presents the obtained coefficients (ratio of eye and whole-body doses) for whole-body dosemeters worn on the left side of the body at chest level. It documents distinctively coefficients for CA/PTCA (angiography/angioplasty), RFA (radio-frequency ablations) and PM and ICD procedures ( pacemaker and defibrillator implantations) as well as a coefficient to be used when the type of procedure performed by the operator is not known. This distinction is particularly important since exposure is strongly dependent on the working conditions, and the table clearly shows smaller uncertainties on the eye/whole-body dose ratio specific per class of procedure. Finally, one should note that the phantom-based coefficients introduced here exclude any exposure variability due to operator movement or to changes in radiation conditions during the procedure. As such, the overall uncertainty on the ratio of eye and the chest left doses is expected to be larger in routine conditions.
ELDO CUMULATIVE EYE LENS DOSE CALCULATION Table 3. Occupational data for 14 interventional cardiologists (C) including the total number of years in practice (Y), total number of procedures per year (P/Y), use of lead glasses and the cumulative whole-body dose for the period where no glasses are worn and for that where lead glasses were systematically used. C
13 20 6 9 10 11 12 15 9 27 4 17 21 13
P/ Y
480 80 160 160 160 480 160 — 480 480 80 800 480 480
Lead glasses
Cumulative wholebody dose (mSv)
Use
Without glasses
With glasses
118 15 51 17 97 22 12 37 47 304 21 63 201 18
26
Yes No No No Yes No No No Yes No No Yes Yes No
Since
2004
2002
2002 1997 2005
58
24 77 7
C
Cumulative left eye lens dose (mSv)
Cumulative right eye lens dose (mSv)
N.A. CA/PTCA and RFA
PM and ICD
N.A. CA/PTCA and RFA
PM and ICD
112 13 45 15 106 19 10 32 50 264 19 83 178 16
90 11 36 12 85 15 8 26 40 213 15 67 143 13
101 11 38 13 103 16 9 27 48 225 16 88 153 13
80 9 30 10 82 13 7 22 38 179 13 70 122 11
1 2 3 4 5 6 7 8 9 10 11 12 13 14
89 11 36 12 84 15 8 25 40 210 15 66 141 12
71 8 27 9 72 11 6 19 34 158 11 62 108 9
Values presented here are calculated considering unknown eyewear models and coefficients from Table 2.
RESULTS AND DISCUSSION Cumulative eye lens dose estimates Table 4 presents the cumulative left and right eye lens doses calculated with the ELDO approach. Calculations were done while considering (a) a lack of knowledge of the procedure type, (b) involvement of the operator with CA/PTCA and RFA procedures only and (c) only PM and ICD procedures. Moreover, the data in this table consider the use of an unknown eyewear model (if applicable). From this table, it is possible to see that the right eye is generally less exposed than the left eye, in agreement with previous findings(8, 11). In addition, radiation exposure to the eyes may sensitively vary from one operator to another even when the same number of years in practice and procedures per year (i.e. workload) are declared. This is mainly due to the work method and environment, to the skills and experience of the operator as well to the radiation protection awareness and culture specific for each operator as also reflected in the Hp(10) records. For the considered physicians, the estimated cumulative left and right eye lens dose ranged from 8 to 264 mSv and 6 to 225 mSv, respectively. These values are comparable with the ones in the literature(9) and remain below the new ICRP lifetime eye dose threshold of 500 mSv. Nonetheless, such values do not imply a null risk of developing radiation-induced cataracts as the doseto-risk relation has not yet been clearly defined. This is also particularly true considering the questionable
precision of the workload questionnaire and the very high calculation uncertainties (cf. next section). Finally, when comparing eye exposure as a function of procedure type, sensitive changes on cumulative doses may be noticed. Namely, the left and right eye doses decreased by almost 21 and 30 %, respectively, when the specific coefficient for CA/PTCA and RFA procedures was used instead of the coefficient for an unknown procedure type. This is mainly due to the sensitive changes in the whole-body-to-eye ratio as a function of tube projection. Meanwhile, the impact of the shape/type of lead glass on eye exposure was found to be lower in the specific case of CA/PTCA and RFA procedures, since the difference in eye lens dose between the wearing of rounded or squared glasses did not vary by .14.5 and 4.5 % for the left and right eyes, respectively. Annual eye lens dose estimates Table 5 presents the annual eye lens dose values whenever these exceeded the limit of 20 mSv. These were calculated while reviewing the annual Hp(10) values for each cardiologist using the whole-body-to-eyedose conversion coefficient of an involvement with unknown type of procedure. Table 5 indicates that 6 out of 14 operators are likely to have exceeded the new annual limit at least once in their career. This risk of excessive dose to the eyes is, however, limited when put against the overall years of practice and considering
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1 2 3 4 5 6 7 8 9 10 11 12 13 14
Y
Table 4. Cumulative eye lens doses calculated from wholebody dose equivalents Hp(10) using the ELDO approach per procedure class.
J. FARAH ET AL. Table 5. Annual eye lens doses calculated using the ELDO approach for those interventional cardiologists who show values exceeding the new 20-mSv annual limit. C
1 3 5
Annual right eye lens dose exceeding 20 mSv
Year
Value (mSv)
Year
Value (mSv)
1997 1998 2001 1999 2001 1999 1988 1999
33 24 23 44 31 24 26 25
1997 1998 — 1999 2001 1999 1988 1999
28 21 — 37 26 20 22 22
Values presented here are given considering cardiologists’ involvement with unknown procedure type.
the relatively unfavourable exposure scenario used here. On the one hand, changing the a priori information on the type of procedures from unknown to known (CA/PTCA, RFA or PM and ICD) shows that only four cardiologists may have an annual eye dose exceeding 20 mSv. On the other hand, nowadays’ improved radiation protection culture (more regular use of ceiling screens and lead glasses) and work conditions (improved X-ray system outputs with significantly less radiation) are expected to considerably reduce operator’s exposure and limit the risk of exceeding the new annual dose limit. As a matter of fact, protection coefficients given in Table 2 for lead glasses, and elsewhere for ceiling shields(12), clearly show that eye dose exceeding the annual limit could easily be avoided if personal and collective protection equipment are systematically and correctly used. It should also be noticed that, for all 14 cardiologists, the 5-y average eye dose would not exceed the new limit under the second statement of ICRP 118(4). Uncertainty analysis Uncertainties associated with the whole-body-to-eyedose and with the glass protection coefficients are a major drawback in this approach for a routine usage. Indeed, Table 1 indicates a spread to the mean wholebody-to-eye-dose coefficient of 87 % (k ¼ 1) if the left eye dose is estimated from the chest left Hp(10) measurement when considering an operator involved in all types of interventional cardiology procedures. This high uncertainty can be reduced with the knowledge of the type of procedure the operator was involved in, although precise information on the whole working period is probably not always available. The second uncertainty component is the one on the glass protection coefficient, which also decreases with the knowledge of the used eyewear model. The combination of
– –
the use of measured eye lens doses from published studies in combination with information on practice and workload and the estimation of eye lens doses from patient dose indicators(7).
Finally, one should always bear in mind that these uncertainties were obtained considering very well-known and conservative hypothesis on exposure conditions (fixed tube and operator positions, fixed field size and beam quality, use of protection equipment, etc.) which do not faithfully reproduce the routine practice where multiple parameters may change at the same time. Therefore, the overall uncertainty on eye lens dose can be higher than the already large uncertainties presented here. As such, the routine monitor of eye lens dose should be done with dedicated dosemeters rather than considering the use of Hp(10) correlations. CONCLUSION This work puts into application the practical and easily exploitable ELDO dosimetry approach to assess cumulative and annual eye lens dose retrospectively. Uncertainties associated with the use of such an approach were also calculated considering different scenarios. Starting from whole-body Hp(10) values, recorded above the lead apron, cumulative eye lens doses were calculated for 14 different interventional cardiologists. Left and right eye lens dose ranged from few mSv to 264 mSv while remaining below the ICRP lifetime eye dose threshold of 500 mSv. Meanwhile, the highest annual eye lens doses occasionally exceeded the new ICRP annual limit; this was never the case when lead glasses were worn. It is important to note that uncertainties associated with this approach are rather large, as expected for any retrospective dosimetric study of this type.
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9 10 13
Annual left eye lens dose exceeding 20 mSv
both uncertainties on whole-body-to-eye-dose and glass protection coefficients results in very high overall uncertainties up to 107 % (k ¼ 1) in the worst case scenario. This latter can be reduced to 45 and 51 % (k ¼ 1), respectively, for the left and right eye, in the best case scenario (PM and ICD procedures and squared lead glasses). Although similar high uncertainty is associated with the radiation risk estimation and the somehow arbitrary limit of 20 mSv per year proposed by ICRP, large uncertainties on eye lens dose estimates discourage the use of such an approach for routine monitoring of eye lens dose. The method remains nonetheless useful for retrospective epidemiological purposes where an uncertainty of 50 –100 % can be tolerated in the absence of an alternative retrospective dosimetry method. To improve the retrospective assessment of eye lens dose and reduce the associated uncertainty, different approaches can be jointly considered including:
ELDO CUMULATIVE EYE LENS DOSE CALCULATION
5.
6.
7.
8.
FUNDING The ELDO project was funded by the DoReMi Network of Excellence.
9.
REFERENCES 1. Miller, D. L., Van˜o´, E., Bartal, G., Balter, S., Dixon, R., Padovani, R., Schueler, B., Cardella, J. F. and de Bae`re, T. 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. 33, 230–239 (2010). 2. Chodick, G., Bekiroglu, N., Hauptmann, M., Alexander, B. H., Freedman, D. M., Doody, M. M., Cheung, L. C., Simon, S. L., Weinstock, R. M., Bouville, A. et al. 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, 620–631 (2008). 3. Worgul, B. V. et al. Cataracts among Chernobyl clean-up workers: implications regarding permissible eye exposures. Radiat. Res. 167, 233–243 (2007). 4. ICRP Publication 118. Statement on tissue reactions/ early and late effects of radiation in normal tissues and
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12.
organs – threshold doses for tissue reactions in a radiation protection context. Ann. ICRP 41(1/2) (2012). Lie, Ø. Ø., Paulsen, G. U. and Wøhni, T. Assessment of effective dose and dose to the lens of the eye for the interventional cardiologist. Radiat. Prot. Dosim. 132, 313–318 (2008). Vano, E., Ubeda, C., Leyton, F., Miranda, P. and Gonzalez, L. staff radiation doses in interventional cardiology: correlation with patient exposure. Pediatr. Cardiol. 30, 409–413 (2009). Dauer, L. T., Thornton, R. H., Solomon, S. B. and St. Germain, J. Unprotected operator eye lens doses in oncologic interventional radiology are clinically significant: estimation from patient kerma-area-product data. J. Vasc. Interv. Radiol. 21, 1859–1861 (2010). Vanhavere, F., Carinou, E., Domienik, J., Donadille, L., Ginjaume, M., Gualdrini, G., Koukorava, C., Krim, S., Nikodemova, D., Ruiz-Lopez, N. et al. Measurements of eye lens doses in interventional radiology and cardiology: final results of the ORAMED project. Radiat. Meas. 46, 1243–1247 (2011). Jacob, S., Donadille, L., Maccia, C., Bar, O., Boveda, S., Laurier, D. and Bernier, M. O. Eye lens radiation exposure to interventional cardiologists: a retrospective assessment of cumulative doses. Radiat. Prot. Dosim. 153, 282–293 (2013). Farah, J., Struelens, L., Jacob, S., Schnelzer, M., Auvinen, A., Vanhavere, F. and Clairand, I. Dosimetry approach for a retrospective epidemiological study on eye lens dose to interventional cardiologists and the occurrence of radiation-induced lens opacities. Proceedings of the 55th AAPM Annual meeting. Med. Phys. 40, 428 (2013). Farah, J., Struelens, L., Dabin, J., Koukorava, C., Donadille, L., Jacob, S., Schnelzer, M., Auvinen, A., Vanhavere, F. and Clairand, I. A correlation study of eye lens dose and personal dose equivalent for interventional cardiologists. Radiat. Prot. Dosim. 157(4), 561–569 (2013). Koukorava, C., Farah, J., Struelens, L., Clairand, I., Donadille, L., Vanhavere, F. and Dimitriou, P. Efficiency of radiation protection equipment in interventional radiology: a systematic Monte Carlo study of eye lens and whole body doses. J. Radiol. Prot. 34, 509– 528 (2014).
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The ELDO approach can be used for retrospective epidemiological studies on interventional cardiologists, but, if possible, it is recommended to use several approaches to assess eye lens dose. For routine monitoring of the eye lens dose, this approach could be used to indicate which individuals are likely to reach annual doses close to the new ICRP annual limit of 20 mSv. For these individuals, the use of dedicated eye lens dosemeters is required to assess the actual eye lens dose. Currently, a large-scale measurement campaign is being organised within the European EURADOS association to further validate this approach and determine other methods that may help in assessing eye lens doses retrospectively for interventional cardiologists.
doi:10.1093/rpd/ncu315
APPLICATION OF THE ELDO APPROACH TO ASSESS CUMULATIVE EYE LENS DOSES FOR INTERVENTIONAL CARDIOLOGISTS
*Corresponding author: Email: [email protected] In preparation of a large European epidemiological study on the relation between eye lens dose and the occurrence of lens opacities, the European ELDO project focused on the development of practical methods to estimate retrospectively cumulative eye lens dose for interventional medical professionals exposed to radiation. The present paper applies one of the ELDO approaches, correlating eye lens dose to whole-body doses, to assess cumulative eye lens dose for 14 different Finnish interventional cardiologists for whom annual whole-body dose records were available for their entire working period. The estimated cumulative left and right eye lens dose ranged from 8 to 264 mSv and 6 to 225 mSv, respectively. In addition, calculations showed annual eye lens doses sometimes exceeding the new ICRP annual limit of 20 mSv. The work also highlights the large uncertainties associated with the application of such an approach proving the need for dedicated dosimetry systems in the routine monitoring of the eye lens dose.
INTRODUCTION The recurrent occupational exposure to radiation of the eye lens has become a real concern for interventional medical professionals since it may lead to the development of lens opacities(1). Recent epidemiological studies have shown that lens opacities may appear for doses lower than previously considered(2 – 3). Measurements of eye lens dose, performed on physicians during interventional procedures, and several studies assessing operator’s eye lens doses from patient dose indicators, have shown that the new annual limit of 20 mSv recommended by the ICRP(4) can be exceeded in numerous cases(5 – 9). In preparation of a large European epidemiological study on the relation between eye lens dose and the occurrence of lens opacities, the European ELDO project focused on the development of practical methods to estimate cumulative eye lens dose for interventional radiologists and cardiologists. Two approaches(10) were introduced within ELDO to estimate eye lens dose starting from available data. In the first approach, a mean eye lens dose for specific procedures—recently established within the European ORAMED(8) project—is used in combination with collected information regarding workload, X-ray system and radiation protection devices used. This
method accounts for the evolution of X-ray systems and procedures over the last 50 y and its influence on eye lens dose to the medical worker. In the second approach, eye lens dose is estimated directly from whole-body dose equivalents, Hp(10), measured above the lead apron. The present paper applies the second ELDO approach to assess cumulative eye lens dose for 14 different Finnish interventional cardiologists for whom annual whole-body doses, recorded above the lead apron, were available for their entire working period. The work also calculates annual eye lens doses and compares those with the new ICRP annual limit (4). Finally, uncertainties associated with the use of such an approach are calculated to investigate its viability for routine monitoring purposes as well as for retrospective epidemiological studies. MATERIALS AND METHODS Eye lens dose correlation to whole-body dose The ELDO project included a large phantom-based measurement campaign carried out in typical interventional settings considering different tube projections beam energies, operator positions and access routes and using both mono-tube and biplane X-ray
# The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
Downloaded from http://rpd.oxfordjournals.org/ at New York University on October 19, 2014
J. Farah1, L. Struelens2, A. Auvinen3, S. Jacob1, C. Koukorava4, M. Schnelzer5, F. Vanhavere2 and I. Clairand1 1 Laboratoire de Dosime´trie des Rayonnements Ionisants, Institut de Radioprotection et de Suˆrete´ Nucle´aire (IRSN) – PRP-HOM/SDE – BP17, Fontenay-aux-Roses Cedex 92262, France 2 Department of Radiation Protection Dosimetry and Calibration, Belgian Nuclear Research Centre, Boeretang 200, Mol BE-2400, Belgium 3 Research and Environmental Surveillance Department, Radiation and Nuclear Safety Authority, PO BOX 14, Helsinki 00881, Finland 4 Division of Licensing and Inspections, Greek Atomic Energy Commission, PO Box 60092, Ag. Paraskevi, Athens 15310, Greece 5 Radiation Epidemiology Unit, Federal Office for Radiation Protection, Ingolsta¨dter Landstraße 1, Oberschleißheim 85764, Germany
J. FARAH ET AL.
Accounting for radiation protection equipment Within the ELDO project, for practical reasons, all measurements excluded the use of radiation protection equipment. Thus, in addition within this same project, Monte Carlo simulations were considered to provide the necessary correction coefficients that account for the impact of personal and collective radiation protection equipment on eye and whole-body Table 1. Ratio of left/right eye lens dose and on phantom chest left Hp(10) value, specific per type of procedure: (a) unknown class (N.A.), (b) CA/PTCA and RFA and (c) PM and ICD. Procedure type
N.A. CA/PTCA and RFA PM and ICD
Ratio eye lens dose/ Hp(10)chest,left
Uncertainty (%)
Left eye
Right eye
Left eye
Right eye
0.87 0.69 0.70
0.74 0.52 0.59
87 52 23
85 62 33
Values taken from Farah et al.(11) Uncertainty coefficients (k ¼ 1) are given as the spread of the ratio of eye dose/Hp(10) as a function of beam projection, operator position, etc.
doses(12). Table 2 provides the results of the profound simulation study in which the radiation protection efficiency of different eyewear models was determined considering again various clinical interventional conditions. As the protection efficiency can be very different depending on the shape of the lead glasses, a correction coefficient is given separately for two basic models representing typical rounded and squared glasses. A distinct coefficient is also given for cases where the glass model is unknown; this coefficient represents the average protection obtained with MC simulation considering altogether both eyewear models and all working conditions. The spread on all simulations (.100 scenarios considered) of the average simulated protection coefficients is also documented in Table 2. One should again note that the protection coefficients, obtained from MC simulations, do not include uncertainty due to changes in operator position or beam quality throughout the intervention. Data of Hp(10) records and work conditions To determine cumulative eye lens doses using this ELDO approach, whole-body dose equivalents measured above the lead apron are required for the entire working period. Table 3 documents the data available for 14 different Finnish interventional cardiologists including the number of years in practice, annual workload, type of procedures typically done and the use of radiation protection equipment. None of the interviewed cardiologists indicated ever using ceilingsuspended screens. Only few operators reported the use of lead glasses, without any specification on the model, as of a certain moment in their career. One should note, finally, that the recorded cumulative Hp(10) values may not reflect the exact exposure to radiation as the systematic wearing of whole-body dosemeters cannot be guaranteed. Table 2. Protection coefficient, ratio of Hp(3) doses with/ without the lead glasses, specific for unknown eyewear model, rounded eye glasses and squared models. Eyewear model
N.A. Rounded Squared
Protection coefficient
Uncertainty (%)
Left eye
Right eye
Left eye
Right eye
0.42 0.26 0.60
0.72 0.79 0.69
62 63 39
37 30 39
Values taken from Koukorava et al.(12) Uncertainty coefficients (k ¼ 1) are given as the spread of the ratio of protection coefficients as a function of beam projection, operator position, etc.
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systems(11). Measurements showed that eye lens dose correlates best with Hp(10) registered on the left side of the phantom at the level of the collar. This correlation, however, implicates high uncertainties, with a Standard Deviation of 41 % on the average ratio between eye lens dose and Hp(10). In addition, since such a wearing position of the dosemeter is not typical, the correlation to the whole-body dose measured on the left side of the chest was also considered. Table 1 presents the obtained coefficients (ratio of eye and whole-body doses) for whole-body dosemeters worn on the left side of the body at chest level. It documents distinctively coefficients for CA/PTCA (angiography/angioplasty), RFA (radio-frequency ablations) and PM and ICD procedures ( pacemaker and defibrillator implantations) as well as a coefficient to be used when the type of procedure performed by the operator is not known. This distinction is particularly important since exposure is strongly dependent on the working conditions, and the table clearly shows smaller uncertainties on the eye/whole-body dose ratio specific per class of procedure. Finally, one should note that the phantom-based coefficients introduced here exclude any exposure variability due to operator movement or to changes in radiation conditions during the procedure. As such, the overall uncertainty on the ratio of eye and the chest left doses is expected to be larger in routine conditions.
ELDO CUMULATIVE EYE LENS DOSE CALCULATION Table 3. Occupational data for 14 interventional cardiologists (C) including the total number of years in practice (Y), total number of procedures per year (P/Y), use of lead glasses and the cumulative whole-body dose for the period where no glasses are worn and for that where lead glasses were systematically used. C
13 20 6 9 10 11 12 15 9 27 4 17 21 13
P/ Y
480 80 160 160 160 480 160 — 480 480 80 800 480 480
Lead glasses
Cumulative wholebody dose (mSv)
Use
Without glasses
With glasses
118 15 51 17 97 22 12 37 47 304 21 63 201 18
26
Yes No No No Yes No No No Yes No No Yes Yes No
Since
2004
2002
2002 1997 2005
58
24 77 7
C
Cumulative left eye lens dose (mSv)
Cumulative right eye lens dose (mSv)
N.A. CA/PTCA and RFA
PM and ICD
N.A. CA/PTCA and RFA
PM and ICD
112 13 45 15 106 19 10 32 50 264 19 83 178 16
90 11 36 12 85 15 8 26 40 213 15 67 143 13
101 11 38 13 103 16 9 27 48 225 16 88 153 13
80 9 30 10 82 13 7 22 38 179 13 70 122 11
1 2 3 4 5 6 7 8 9 10 11 12 13 14
89 11 36 12 84 15 8 25 40 210 15 66 141 12
71 8 27 9 72 11 6 19 34 158 11 62 108 9
Values presented here are calculated considering unknown eyewear models and coefficients from Table 2.
RESULTS AND DISCUSSION Cumulative eye lens dose estimates Table 4 presents the cumulative left and right eye lens doses calculated with the ELDO approach. Calculations were done while considering (a) a lack of knowledge of the procedure type, (b) involvement of the operator with CA/PTCA and RFA procedures only and (c) only PM and ICD procedures. Moreover, the data in this table consider the use of an unknown eyewear model (if applicable). From this table, it is possible to see that the right eye is generally less exposed than the left eye, in agreement with previous findings(8, 11). In addition, radiation exposure to the eyes may sensitively vary from one operator to another even when the same number of years in practice and procedures per year (i.e. workload) are declared. This is mainly due to the work method and environment, to the skills and experience of the operator as well to the radiation protection awareness and culture specific for each operator as also reflected in the Hp(10) records. For the considered physicians, the estimated cumulative left and right eye lens dose ranged from 8 to 264 mSv and 6 to 225 mSv, respectively. These values are comparable with the ones in the literature(9) and remain below the new ICRP lifetime eye dose threshold of 500 mSv. Nonetheless, such values do not imply a null risk of developing radiation-induced cataracts as the doseto-risk relation has not yet been clearly defined. This is also particularly true considering the questionable
precision of the workload questionnaire and the very high calculation uncertainties (cf. next section). Finally, when comparing eye exposure as a function of procedure type, sensitive changes on cumulative doses may be noticed. Namely, the left and right eye doses decreased by almost 21 and 30 %, respectively, when the specific coefficient for CA/PTCA and RFA procedures was used instead of the coefficient for an unknown procedure type. This is mainly due to the sensitive changes in the whole-body-to-eye ratio as a function of tube projection. Meanwhile, the impact of the shape/type of lead glass on eye exposure was found to be lower in the specific case of CA/PTCA and RFA procedures, since the difference in eye lens dose between the wearing of rounded or squared glasses did not vary by .14.5 and 4.5 % for the left and right eyes, respectively. Annual eye lens dose estimates Table 5 presents the annual eye lens dose values whenever these exceeded the limit of 20 mSv. These were calculated while reviewing the annual Hp(10) values for each cardiologist using the whole-body-to-eyedose conversion coefficient of an involvement with unknown type of procedure. Table 5 indicates that 6 out of 14 operators are likely to have exceeded the new annual limit at least once in their career. This risk of excessive dose to the eyes is, however, limited when put against the overall years of practice and considering
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1 2 3 4 5 6 7 8 9 10 11 12 13 14
Y
Table 4. Cumulative eye lens doses calculated from wholebody dose equivalents Hp(10) using the ELDO approach per procedure class.
J. FARAH ET AL. Table 5. Annual eye lens doses calculated using the ELDO approach for those interventional cardiologists who show values exceeding the new 20-mSv annual limit. C
1 3 5
Annual right eye lens dose exceeding 20 mSv
Year
Value (mSv)
Year
Value (mSv)
1997 1998 2001 1999 2001 1999 1988 1999
33 24 23 44 31 24 26 25
1997 1998 — 1999 2001 1999 1988 1999
28 21 — 37 26 20 22 22
Values presented here are given considering cardiologists’ involvement with unknown procedure type.
the relatively unfavourable exposure scenario used here. On the one hand, changing the a priori information on the type of procedures from unknown to known (CA/PTCA, RFA or PM and ICD) shows that only four cardiologists may have an annual eye dose exceeding 20 mSv. On the other hand, nowadays’ improved radiation protection culture (more regular use of ceiling screens and lead glasses) and work conditions (improved X-ray system outputs with significantly less radiation) are expected to considerably reduce operator’s exposure and limit the risk of exceeding the new annual dose limit. As a matter of fact, protection coefficients given in Table 2 for lead glasses, and elsewhere for ceiling shields(12), clearly show that eye dose exceeding the annual limit could easily be avoided if personal and collective protection equipment are systematically and correctly used. It should also be noticed that, for all 14 cardiologists, the 5-y average eye dose would not exceed the new limit under the second statement of ICRP 118(4). Uncertainty analysis Uncertainties associated with the whole-body-to-eyedose and with the glass protection coefficients are a major drawback in this approach for a routine usage. Indeed, Table 1 indicates a spread to the mean wholebody-to-eye-dose coefficient of 87 % (k ¼ 1) if the left eye dose is estimated from the chest left Hp(10) measurement when considering an operator involved in all types of interventional cardiology procedures. This high uncertainty can be reduced with the knowledge of the type of procedure the operator was involved in, although precise information on the whole working period is probably not always available. The second uncertainty component is the one on the glass protection coefficient, which also decreases with the knowledge of the used eyewear model. The combination of
– –
the use of measured eye lens doses from published studies in combination with information on practice and workload and the estimation of eye lens doses from patient dose indicators(7).
Finally, one should always bear in mind that these uncertainties were obtained considering very well-known and conservative hypothesis on exposure conditions (fixed tube and operator positions, fixed field size and beam quality, use of protection equipment, etc.) which do not faithfully reproduce the routine practice where multiple parameters may change at the same time. Therefore, the overall uncertainty on eye lens dose can be higher than the already large uncertainties presented here. As such, the routine monitor of eye lens dose should be done with dedicated dosemeters rather than considering the use of Hp(10) correlations. CONCLUSION This work puts into application the practical and easily exploitable ELDO dosimetry approach to assess cumulative and annual eye lens dose retrospectively. Uncertainties associated with the use of such an approach were also calculated considering different scenarios. Starting from whole-body Hp(10) values, recorded above the lead apron, cumulative eye lens doses were calculated for 14 different interventional cardiologists. Left and right eye lens dose ranged from few mSv to 264 mSv while remaining below the ICRP lifetime eye dose threshold of 500 mSv. Meanwhile, the highest annual eye lens doses occasionally exceeded the new ICRP annual limit; this was never the case when lead glasses were worn. It is important to note that uncertainties associated with this approach are rather large, as expected for any retrospective dosimetric study of this type.
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Annual left eye lens dose exceeding 20 mSv
both uncertainties on whole-body-to-eye-dose and glass protection coefficients results in very high overall uncertainties up to 107 % (k ¼ 1) in the worst case scenario. This latter can be reduced to 45 and 51 % (k ¼ 1), respectively, for the left and right eye, in the best case scenario (PM and ICD procedures and squared lead glasses). Although similar high uncertainty is associated with the radiation risk estimation and the somehow arbitrary limit of 20 mSv per year proposed by ICRP, large uncertainties on eye lens dose estimates discourage the use of such an approach for routine monitoring of eye lens dose. The method remains nonetheless useful for retrospective epidemiological purposes where an uncertainty of 50 –100 % can be tolerated in the absence of an alternative retrospective dosimetry method. To improve the retrospective assessment of eye lens dose and reduce the associated uncertainty, different approaches can be jointly considered including:
ELDO CUMULATIVE EYE LENS DOSE CALCULATION
5.
6.
7.
8.
FUNDING The ELDO project was funded by the DoReMi Network of Excellence.
9.
REFERENCES 1. Miller, D. L., Van˜o´, E., Bartal, G., Balter, S., Dixon, R., Padovani, R., Schueler, B., Cardella, J. F. and de Bae`re, T. 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. 33, 230–239 (2010). 2. Chodick, G., Bekiroglu, N., Hauptmann, M., Alexander, B. H., Freedman, D. M., Doody, M. M., Cheung, L. C., Simon, S. L., Weinstock, R. M., Bouville, A. et al. 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, 620–631 (2008). 3. Worgul, B. V. et al. Cataracts among Chernobyl clean-up workers: implications regarding permissible eye exposures. Radiat. Res. 167, 233–243 (2007). 4. ICRP Publication 118. Statement on tissue reactions/ early and late effects of radiation in normal tissues and
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organs – threshold doses for tissue reactions in a radiation protection context. Ann. ICRP 41(1/2) (2012). Lie, Ø. Ø., Paulsen, G. U. and Wøhni, T. Assessment of effective dose and dose to the lens of the eye for the interventional cardiologist. Radiat. Prot. Dosim. 132, 313–318 (2008). Vano, E., Ubeda, C., Leyton, F., Miranda, P. and Gonzalez, L. staff radiation doses in interventional cardiology: correlation with patient exposure. Pediatr. Cardiol. 30, 409–413 (2009). Dauer, L. T., Thornton, R. H., Solomon, S. B. and St. Germain, J. Unprotected operator eye lens doses in oncologic interventional radiology are clinically significant: estimation from patient kerma-area-product data. J. Vasc. Interv. Radiol. 21, 1859–1861 (2010). Vanhavere, F., Carinou, E., Domienik, J., Donadille, L., Ginjaume, M., Gualdrini, G., Koukorava, C., Krim, S., Nikodemova, D., Ruiz-Lopez, N. et al. Measurements of eye lens doses in interventional radiology and cardiology: final results of the ORAMED project. Radiat. Meas. 46, 1243–1247 (2011). Jacob, S., Donadille, L., Maccia, C., Bar, O., Boveda, S., Laurier, D. and Bernier, M. O. Eye lens radiation exposure to interventional cardiologists: a retrospective assessment of cumulative doses. Radiat. Prot. Dosim. 153, 282–293 (2013). Farah, J., Struelens, L., Jacob, S., Schnelzer, M., Auvinen, A., Vanhavere, F. and Clairand, I. Dosimetry approach for a retrospective epidemiological study on eye lens dose to interventional cardiologists and the occurrence of radiation-induced lens opacities. Proceedings of the 55th AAPM Annual meeting. Med. Phys. 40, 428 (2013). Farah, J., Struelens, L., Dabin, J., Koukorava, C., Donadille, L., Jacob, S., Schnelzer, M., Auvinen, A., Vanhavere, F. and Clairand, I. A correlation study of eye lens dose and personal dose equivalent for interventional cardiologists. Radiat. Prot. Dosim. 157(4), 561–569 (2013). Koukorava, C., Farah, J., Struelens, L., Clairand, I., Donadille, L., Vanhavere, F. and Dimitriou, P. Efficiency of radiation protection equipment in interventional radiology: a systematic Monte Carlo study of eye lens and whole body doses. J. Radiol. Prot. 34, 509– 528 (2014).
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The ELDO approach can be used for retrospective epidemiological studies on interventional cardiologists, but, if possible, it is recommended to use several approaches to assess eye lens dose. For routine monitoring of the eye lens dose, this approach could be used to indicate which individuals are likely to reach annual doses close to the new ICRP annual limit of 20 mSv. For these individuals, the use of dedicated eye lens dosemeters is required to assess the actual eye lens dose. Currently, a large-scale measurement campaign is being organised within the European EURADOS association to further validate this approach and determine other methods that may help in assessing eye lens doses retrospectively for interventional cardiologists.
