EURADOS 2016 INTERCOMPARISON EXERCISE OF EYE LENS DOSEMETERS

EURADOS 2016 INTERCOMPARISON EXERCISE OF EYE LENS DOSEMETERS Abstract In the context of a new annual eye lens dose limit for occupational exposure equal to 20 mSv, European Radiation Dosimetry Group (EURADOS) organized an intercomparison dedicated to eye lens dosemeters, including photon and beta radiations. The objective was to complete the first intercomparison recently organized by EURADOS for photons and to update the overview of eye lens dosemeters available in Europe. The dosemeters provided by the 22 participants coming from 12 countries were all composed of thermoluminescent detectors. The dosemeters were irradiated with photon and beta fields defined in relevant standards. The results, provided by participants in terms of Hp(3), were compared to the reference delivered doses. Results are globally satisfactory for photons since 90% of the data are in accordance to the ISO 14146 standard requirements. The respective values for betas stress the fact that dosemeters designed for Hp(0.07) are not suitable to monitor the eye lens dose in case of betas. INTRODUCTION The European Radiation Dosimetry Group (EURADOS) organizes regularly intercomparison (IC) exercises(1, 2) dedicated to the harmonization of Individual Monitoring Services (IMS). In the context of the revised European Basic Safety Standards Directive 2013/59/EURATOM(3), stating a new eye lens dose limit for occupational exposure equal to 20 mSv per year, EURADOS organized in 2014, for the first time, an IC exercise specifically dedicated for eye lens dosemeters in the medical photon fields, so called IC2014eye(4). In 2016, EURADOS decided to organize a second IC dedicated to eye lens dosemeters, so called IC2016eye, including not only photon beams but also beta radiations. The main objective of this work was to provide a general overview of the IMS capacity to measure Hp(3), both for photon and beta radiations. The detailed analysis of the results is limited by the organizers’ commitment that all the results would be treated anonymously in scientific publications. MATERIAL AND METHODS Scope and organization of IC2016eye This IC for eye lens dosemeters (IC2016eye) was managed and coordinated on behalf of EURADOS by an Organization Group (OG) composed of members of EURADOS. As usual for this type of exercise, the IC was designed to be a blind test for all participants who reported their results without knowing the reference dose values. For photon radiation fields, the only information given was that the irradiations would be performed in S-Cs and in photon fields representative of medical workplaces, without knowing the exact beam qualities. Regarding the beta radiation fields, participants were informed that the beam qualities chosen were 85Kr, 90Sr+90Y and 106Ru+106Rh. Still, the participants did not know which dosemeter would be irradiated to which type of radiation (photons or betas). The low-energy beta quality (85Kr, 0.24 MeV) was chosen to test the design of the dosemeters concerning a sufficient filter in front of the detector. Even when this quality is not used in practice, such energies are produced by partially shielded high energy beta sources and are therefore of relevance. All participants were requested to prepare their dosemeters according to their usual procedures. Participants were asked to report the doses in terms of Hp(3) using their routine protocol. All the data were processed by the OG members and were treated confidentially using an identification code assigned to each participant. Participants The participants were coming from 22 IMS from 12 different countries (Bulgaria, Czech Republic, France, Germany, Israel, Italy, Slovakia, Spain, Switzerland, Turkey, UK and USA). All the provided dosemeters were composed of thermoluminescent detectors. Among the 22 participants, 6 provided the Eye-DTM system developed during the ORAMED European project(5), 3 provided dosemeters with a specific holder to be worn at the level of the eyes, 11 provided dosemeters placed in a plastic bag and 2 provided whole body dosemeters. A picture of all the dosemeters is presented in Figure 1. In addition, most of the participants indicated via a questionnaire some technical information such as the type of the included detector, the filter used if any, as well as the phantom and energy quality used for calibration. Regarding the calibration, 13 participants use pure S-Cs or pure S-Co or both, 1 uses mixed S-Cs and X-ray and 8 use various X-ray spectra. Figure 1. View largeDownload slide Dosemeters provided by the participants (Photo credit PTB). Figure 1. View largeDownload slide Dosemeters provided by the participants (Photo credit PTB). In total, these 22 IMS deliver around 30 000 eye lens dosemeters per year. Irradiation conditions Tables 1 and 2 summarize the irradiation conditions for photon and beta qualities, respectively. The chosen radiation qualities were S-Cs and N-100 defined in ISO 4037-1 standard(6), RQR6 defined in IEC 61267 standard(7) and beta radiation field series defined in ISO 6980-1 standard(8). The irradiations were performed on a cylindrical head phantom (20 cm × 20 cm)(9) developed during the ORAMED European project(5) and mentioned in ISO 15382(10) as well as in the current draft (DIS) of ISO 4037-3(11). Conversion coefficients to relate air kerma to Hp(3) were taken from Behrens(12) for ISO 4037 qualities, from Principi et al.(13) for IEC 61267 qualities and from Behrens et al.(14, 15) for beta radiation qualities. Two dosemeters of each participant were irradiated for each setup. The irradiations were carried out at PTB (Germany) and NIOM (Poland) calibration laboratories. Table 1. Irradiation plan for photon qualities. Radiation quality and angle of incidence Mean energy (keV) Dose range Hp(3) (mSv) RQR6; 0° 44 2.0–3.0 RQR6; 45° 44 2.0–3.0 RQR6; 75° 44 2.0–3.0 N-100; 0° 85 2.0–3.0 S-Cs; 0° 662 2.0–3.0 S-Cs; 60° 662 2.0–3.0 Radiation quality and angle of incidence Mean energy (keV) Dose range Hp(3) (mSv) RQR6; 0° 44 2.0–3.0 RQR6; 45° 44 2.0–3.0 RQR6; 75° 44 2.0–3.0 N-100; 0° 85 2.0–3.0 S-Cs; 0° 662 2.0–3.0 S-Cs; 60° 662 2.0–3.0 Table 1. Irradiation plan for photon qualities. Radiation quality and angle of incidence Mean energy (keV) Dose range Hp(3) (mSv) RQR6; 0° 44 2.0–3.0 RQR6; 45° 44 2.0–3.0 RQR6; 75° 44 2.0–3.0 N-100; 0° 85 2.0–3.0 S-Cs; 0° 662 2.0–3.0 S-Cs; 60° 662 2.0–3.0 Radiation quality and angle of incidence Mean energy (keV) Dose range Hp(3) (mSv) RQR6; 0° 44 2.0–3.0 RQR6; 45° 44 2.0–3.0 RQR6; 75° 44 2.0–3.0 N-100; 0° 85 2.0–3.0 S-Cs; 0° 662 2.0–3.0 S-Cs; 60° 662 2.0–3.0 Table 2. Irradiation plan for beta qualities. Radiation quality and angle of incidence Mean energy (MeV) Dose range Hp(3) (mSv) 85Kr; 0° 0.24 0.03–0.04 90Sr+90Y; 0° 0.8 2.0–3.0 90Sr+90Y; 60° 0.8 2.0–3.0 106Ru+106Rh; 0° 1.2 1.0–1.5 Radiation quality and angle of incidence Mean energy (MeV) Dose range Hp(3) (mSv) 85Kr; 0° 0.24 0.03–0.04 90Sr+90Y; 0° 0.8 2.0–3.0 90Sr+90Y; 60° 0.8 2.0–3.0 106Ru+106Rh; 0° 1.2 1.0–1.5 Table 2. Irradiation plan for beta qualities. Radiation quality and angle of incidence Mean energy (MeV) Dose range Hp(3) (mSv) 85Kr; 0° 0.24 0.03–0.04 90Sr+90Y; 0° 0.8 2.0–3.0 90Sr+90Y; 60° 0.8 2.0–3.0 106Ru+106Rh; 0° 1.2 1.0–1.5 Radiation quality and angle of incidence Mean energy (MeV) Dose range Hp(3) (mSv) 85Kr; 0° 0.24 0.03–0.04 90Sr+90Y; 0° 0.8 2.0–3.0 90Sr+90Y; 60° 0.8 2.0–3.0 106Ru+106Rh; 0° 1.2 1.0–1.5 Results evaluation The numerical results in this IC are reported as the dosemeter response R, where R is defined as the ratio of the value of the dose reported by the participant and corrected for transit dose, Hs, divided by the reference value, Hp(3)c, given by the irradiation laboratory. The performance limits according to the ISO 14146 standard(16), commonly known as ‘trumpet curves’, were adopted to analyze the results: 1F(1−2H0H0+Hc)≤R≤F(1+H02H0+Hc) (1) where Hc is the conventional quantity value (Hp(3)c in the present case), R is the response, F = 1.5 according to the recommendations of ICRP 75 report(17). H0, the ‘lower limit of the dose range for which the system has been approved’, was chosen equal to 0.3 mSv according to the current revision draft of ISO 14146 standard(18). RESULTS AND DISCUSSION Photon qualities Figure 2 gives a general overview of the response values R as a function of the reference doses Hc for photon qualities. It can be noticed that, globally, 90% of the results are within the trumpet curves built according to equation (1). This percentage differs with irradiations setups. Indeed, it is equal to 98% for S-Cs setups and 95% for N-100. This result is consistent with the fact that these qualities are very often used for calibration purposes by the participants. The percentage of results meeting the criteria specified by the trumpet curves decreases for lower energies setups, it is 89 and 84% for ‘RQR6; 0°’ and 45°, respectively. The lowest value is 77% for the ‘RQR6; 75°’ setup which corresponds to low energy and large angle irradiation setup. Figure 2. View largeDownload slide Summary of all reported response values R as a function of reference dose for all the participants for photon qualities. Figure 2. View largeDownload slide Summary of all reported response values R as a function of reference dose for all the participants for photon qualities. Figure 3 gives the distribution of the response values for each irradiation setup using a box plot representation showing the minimum, first quartile, median, third quartile and maximum responses. The median of responses is around 0.9 for S-Cs and N-100 qualities and around 1.2 for RQR series. Figure 3. View largeDownload slide Box plots showing the minimum, first quartile, median, third quartile and maximum responses per irradiation setup for photon qualities. Figure 3. View largeDownload slide Box plots showing the minimum, first quartile, median, third quartile and maximum responses per irradiation setup for photon qualities. Figure 4 presents the distribution of results, using box plots, for each participant in an anonymous manner. A relatively large variability is observed among participants, the median of responses ranges from 0.7 to 1.6. Among the 22 participants, 15 have results that are 100% within the limits set by the ISO 14146 standard(16) for all setups with photon qualities; three have all measurements within the trumpet curves for all photon radiation qualities except for the large angle setup ‘RQR6, 75°’; two have all measurements within the trumpet curves for all photon radiation qualities except for all low-energy setups (RQR6) and two failed in more than three irradiation setups. The difficulties noticed for large angle irradiation setups are more frequently observed for dosemeters placed in plastic bags, but this is not systematic and the difficulties occur as well for other types of dosemeters. Figure 4. View largeDownload slide Box plots showing the minimum, first quartile, median, third quartile and maximum responses for each participant for photon qualities. Figure 4. View largeDownload slide Box plots showing the minimum, first quartile, median, third quartile and maximum responses for each participant for photon qualities. These results do not show any obvious link with the beam quality used by participants for the calibration. A deeper analysis of this type cannot be carried out due to the relatively low number of participants and the variety of dosimeters used as well as the obligation to maintain the anonymity of results. The results observed in this IC for photon qualities are quite similar to the ones observed during the first IC of this type organized in 2014 by EURADOS(4). The spread of the results is slightly larger in the present IC but the median for all photon qualities is close to 1 for both IC. The same difficulties for setups with large angles are observed. Beta qualities Figure 5 gives a general overview of the response values R as a function of the reference doses HC for beta qualities. It can be noticed that only 56% of the results are within the trumpet curves built according to equation (1). This percentage differs very significantly with irradiation setups. For highest energy betas of 106Ru+106Rh, 91% of results are within the trumpet curves. However, for lower energy betas, the percentages decrease dramatically, 47% for 90Sr+90Y and 41% for 85Kr. Figure 5. View largeDownload slide Summary of all reported response values R as a function of reference dose for all the participants for beta qualities. Figure 5. View largeDownload slide Summary of all reported response values R as a function of reference dose for all the participants for beta qualities. It is important to notice that, for technical reasons (extremely long irradiation times), the conventional quantity value for 85Kr was relatively low (Hp(3) = 0.031 mSv as only photon radiation contributes to that quantity due to the rather low beta maximum energy of ~0.69 MeV). This value is below the usual reporting level and below the lower detection limit (LLD) of most IMS. Consequently, it is considered in this IC, that for the participants that, for 85Kr, provided a measurement equal or below their LLD, the response is correct. However, R could not be calculated and thus their data are not included in Figures 5 and 6. This is the case for five participants. Figure 6. View largeDownload slide Box plots showing the minimum, first quartile, median, third quartile and maximum responses per irradiation setup for beta qualities. Figure 6. View largeDownload slide Box plots showing the minimum, first quartile, median, third quartile and maximum responses per irradiation setup for beta qualities. Figure 6 gives the distribution of the response value for each irradiation setup using a box plot representation. It can be noticed that the median of responses ranges from 0.96 to 1.9 for all betas setups except for 85Kr for which large overresponses are observed with a median equal to 154. Among the 22 participants, only 1 has results that are 100% within the limits set by the ISO 14146 standard(16) for all setups with beta qualities. For 106Ru+106Rh, 20 participants are within the trumpet curves, while this number drops to 10 and 8 for 90Sr+90Y 0° and 60°, respectively. Regarding the participants with responses outside the trumpet curves for these beam qualities, no obvious link was found with the type of dosemeter, according to the information given by the participants. In the case of 85Kr, four participants are within the trumpet curves plus the five that provided data below LLD. All dosemeters providing a response within the curves for 85Kr are designed for Hp(3), except for one case. A relatively large variability is observed among participants, the median of responses ranges from 0.6 to 13.5. Figure 7 presents results using a box plot representation, excluding results for Kr-85; in this case, the median ranges from 0.6 to 9.8. Figure 7. View largeDownload slide Box plots showing the minimum, first quartile, median, third quartile and maximum responses for each participant for beta qualities excluding results for 85Kr. Participants marked with * gave results outside of the trumpet curves for 85Kr. Figure 7. View largeDownload slide Box plots showing the minimum, first quartile, median, third quartile and maximum responses for each participant for beta qualities excluding results for 85Kr. Participants marked with * gave results outside of the trumpet curves for 85Kr. In total, two participants are out of the limits for all the beta qualities, and six participants are out of the limits for 90Sr+90Y and 85Kr. For 85Kr radiation large overresponses are observed for some dosemeters. All dosemeters (except for one participant) with an over-response to 85Kr are designed for the measurement of Hp(0.07), because there is an insufficient filter in front of the detector. Indeed, 85Kr has a beta maximum energy of about 0.69 MeV, which does not contribute to the delivered Hp(3) dose, with the exception of the respective small photon contribution (514 keV). For 90Sr+90Y and 106Ru+106Rh, the overresponses are lower, because betas contribute significantly to Hp(3) compared to 85Kr. This issue was already pointed out in a similar IC performed in Germany(19). CONCLUSION EURADOS organized an IC exercise specifically dedicated for eye lens dosemeters, including tests with photon beams and, for the first time, beta fields. The main objective of this IC was to provide an updated overview of the different dosimetry systems currently available for eye lens dose monitoring. It is noticed that only one dosemeter gives a correct response for all qualities tested, i.e. for photon and beta radiation fields, this dosemeter is a TLD, placed in a plastic bag, calibrated in Hp(3). Results are globally satisfactory for photon qualities, whatever the type of dosemeters, since 90% of the results are in accordance to the ISO 14146 standard(16) requirements. For a minority of participants, some discrepancies between the results and reference doses were observed in the case of the irradiations setups characterized by large angles and/or low energies. These results are very similar to those observed in the case of the previous eye lens dosemeter IC organized by EURADOS(4), where 90% of the results were in accordance to the standard. Results for betas are less satisfactory and illustrate the difficulties in measuring beta radiation. The main observed problem was an over-estimate of Hp(3) for low beta energy. The intercomparison demonstrates that dosemeters designed for Hp(0.07) are, in general, not suitable to monitor the dose to the eye lens in case of betas because the filter placed in front of the detector is too thin. Dosemeters designed for Hp(0.07) are suitable for monitoring the eye lens dose only in pure photon radiation workplaces but not in workplaces with significant contributions of beta radiation. Dosemeters well designed for Hp(3), i.e. optimized for both photon and beta fields simultaneously are usually able to perform properly eye lens dose monitoring at all workplaces while for other dosemeters this is usually not the case. FUNDING This work was partly founded by the participants to this intercomparison and EURADOS. REFERENCES 1 Grimbergen , T. W. M. , Figel , M. , Romero , A. M. , Stadtmann , H. and McWhan , A. F. EURADOS self-sustained programme of intercomparisons for individual monitoring services . Radiat. Prot. Dosim. 144 ( 1–4 ), 266 – 274 ( 2011 ). Google Scholar CrossRef Search ADS 2 Romero , A. M. , Grimbergen , T. , McWhan , A. , Stadtmann , H. , Fantuzzi , E. , Clairand , I. , Neumaier , S. , Figel , M. and Dombrowski , H. EURADOS intercomparisons in external radiation dosimetry: similarities and differences among exercises for whole-body photon, whole-body neutron, extremity, eye-lens and passive area dosemeters . Radiat. Prot. Dosim. 170 ( 1–4 ), 82 – 85 ( 2016 ). Google Scholar CrossRef Search ADS 3 Council Directive 2013/59/Euratom of 5 December 2013 laying down basic safety standards for protection against the dangers arising from exposure to ionising radiation, and repealing Directives 89/618/Euratom, 90/641/Euratom, 96/29/Euratom, 97/43/Euratom and 2003/122/Euratom. Official Journal L-13 of 17 January 2014. 4 Clairand , I. , Ginjaume , M. , Vanhavere , F. , Carinou , E. , Daures , J. , Denoziere , M. , Silva , E. H. , Roig , M. , Principi , S. and Van Rycheghem , L. First EURADOS intercomparison exercise of eye lens dosemeters for medical applications . Radiat. Prot. Dosim. 170 ( 1–4 ), 21 – 26 ( 2016 ). Google Scholar CrossRef Search ADS 5 Vanhavere , F. et al. . ORAMED: optimization of radiation protection of medical staff. EURADOS report 2012-02, ISSN 2226-8057, ISBN 978-3-943701-01-2. Braunschweig ( 2012 ). 6 International organization for standardization . X and gamma reference radiation for calibrating dosemeters and doserate meters and for determining their response as a function of photon energy—Part 1: radiation characteristics and production methods. ISO 4037-1 (Geneva: ISO) ( 1999 ). 7 International electrotechnical commission (IEC). Medical diagnostic X-ray equipment—radiation conditions for use in the determination of characteristics. 61267 Ed. 2.0. IEC ( 2005 ). 8 International organization for standardization . Nuclear energy—reference beta-particle radiation—Part 1: methods of production. ISO 6980-1 (Geneva: ISO) ( 2006 ). 9 Gualdrini , G. et al. . A new cylindrical phantom for eye lens dosimetry development . Radiat. Meas. 46 ( 11 ), 1231 – 1234 ( 2011 ). Google Scholar CrossRef Search ADS 10 International organization for standardization . Radiological protection—procedures for monitoring the dose to the lens of the eye, the skin and the extremities. ISO 15382 (Geneva: ISO) ( 2015 ). 11 International organization for standardization . X and gamma reference radiation for calibrating dosemeters and doserate meters and for determining their response as a function of photon energy—Part 3: calibration of area and personal dosemeters and the measurement of their response as a function of energy and angle of incidence. ISO/DIS 4037-3 (Geneva: ISO) ( 2017 ). 12 Behrens , R. Air kerma to Hp(3) conversion coefficients for a new cylinder phantom for photon reference radiation qualities . Radiat. Prot. Dosim. 151 ( 3 ), 450 – 455 ( 2012 ). Google Scholar CrossRef Search ADS 13 Principi , S. , Guardiola , C. , Duch , M. A. and Ginjaume , M. Air kerma to Hp(3) conversion coefficients for IEC 61267 RQR X-ray radiation qualities: application to dose monitoring of the lens of the eye in medical diagnostics . Radiat. Prot. Dosim. 170 ( 1–4 ), 45 – 48 ( 2016 ). Google Scholar CrossRef Search ADS 14 Behrens , R. and Buchholz , G. Extensions to the Beta Secondary Standard BSS 2 . J. Instrum. 6 , P11007 ( 2011 ) and Erratum: J. Instrum. 7, E04001 (2012) and Addendum: J. Instrum7, A05001 (2012). Google Scholar CrossRef Search ADS 15 Behrens , R. Correction factors for the ISO rod phantom, a cylinder phantom, and the ICRU sphere for reference beta radiation fields of the BSS 2 . J. Instrum. 10 , P03014 ( 2015 ). Google Scholar CrossRef Search ADS 16 International organization for standardization . Radiation protection—criteria and performance limits for the periodic evaluation of processors of personal dosemeters for X and gamma radiation. ISO 14146 (Geneva: ISO) ( 2000 ). 17 International commission on radiological protection . General principles for the radiation protection of workers. ICRP publication 75. Ann. ICRP 27(1). Pergamon ( 1997 ). 18 ISO/FDIS 14146:2018(E). Radiological protection—criteria and performance limits for the periodic evaluation of dosimetry services. 19 Behrens , R. , Hupe , O. , Busch , F. , Denk , J. , Engelhardt , J. , Günther , K. , Hödlmoser , H. , Jordan , M. and Strohmaier , J. Intercomparison of eye lens dosemeters . Radiat. Prot. Dosim. 174 ( 1 ), 6 – 12 ( 2017 ). © The Author(s) 2018. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Radiation Protection Dosimetry Oxford University Press

EURADOS 2016 INTERCOMPARISON EXERCISE OF EYE LENS DOSEMETERS

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Abstract

Abstract In the context of a new annual eye lens dose limit for occupational exposure equal to 20 mSv, European Radiation Dosimetry Group (EURADOS) organized an intercomparison dedicated to eye lens dosemeters, including photon and beta radiations. The objective was to complete the first intercomparison recently organized by EURADOS for photons and to update the overview of eye lens dosemeters available in Europe. The dosemeters provided by the 22 participants coming from 12 countries were all composed of thermoluminescent detectors. The dosemeters were irradiated with photon and beta fields defined in relevant standards. The results, provided by participants in terms of Hp(3), were compared to the reference delivered doses. Results are globally satisfactory for photons since 90% of the data are in accordance to the ISO 14146 standard requirements. The respective values for betas stress the fact that dosemeters designed for Hp(0.07) are not suitable to monitor the eye lens dose in case of betas. INTRODUCTION The European Radiation Dosimetry Group (EURADOS) organizes regularly intercomparison (IC) exercises(1, 2) dedicated to the harmonization of Individual Monitoring Services (IMS). In the context of the revised European Basic Safety Standards Directive 2013/59/EURATOM(3), stating a new eye lens dose limit for occupational exposure equal to 20 mSv per year, EURADOS organized in 2014, for the first time, an IC exercise specifically dedicated for eye lens dosemeters in the medical photon fields, so called IC2014eye(4). In 2016, EURADOS decided to organize a second IC dedicated to eye lens dosemeters, so called IC2016eye, including not only photon beams but also beta radiations. The main objective of this work was to provide a general overview of the IMS capacity to measure Hp(3), both for photon and beta radiations. The detailed analysis of the results is limited by the organizers’ commitment that all the results would be treated anonymously in scientific publications. MATERIAL AND METHODS Scope and organization of IC2016eye This IC for eye lens dosemeters (IC2016eye) was managed and coordinated on behalf of EURADOS by an Organization Group (OG) composed of members of EURADOS. As usual for this type of exercise, the IC was designed to be a blind test for all participants who reported their results without knowing the reference dose values. For photon radiation fields, the only information given was that the irradiations would be performed in S-Cs and in photon fields representative of medical workplaces, without knowing the exact beam qualities. Regarding the beta radiation fields, participants were informed that the beam qualities chosen were 85Kr, 90Sr+90Y and 106Ru+106Rh. Still, the participants did not know which dosemeter would be irradiated to which type of radiation (photons or betas). The low-energy beta quality (85Kr, 0.24 MeV) was chosen to test the design of the dosemeters concerning a sufficient filter in front of the detector. Even when this quality is not used in practice, such energies are produced by partially shielded high energy beta sources and are therefore of relevance. All participants were requested to prepare their dosemeters according to their usual procedures. Participants were asked to report the doses in terms of Hp(3) using their routine protocol. All the data were processed by the OG members and were treated confidentially using an identification code assigned to each participant. Participants The participants were coming from 22 IMS from 12 different countries (Bulgaria, Czech Republic, France, Germany, Israel, Italy, Slovakia, Spain, Switzerland, Turkey, UK and USA). All the provided dosemeters were composed of thermoluminescent detectors. Among the 22 participants, 6 provided the Eye-DTM system developed during the ORAMED European project(5), 3 provided dosemeters with a specific holder to be worn at the level of the eyes, 11 provided dosemeters placed in a plastic bag and 2 provided whole body dosemeters. A picture of all the dosemeters is presented in Figure 1. In addition, most of the participants indicated via a questionnaire some technical information such as the type of the included detector, the filter used if any, as well as the phantom and energy quality used for calibration. Regarding the calibration, 13 participants use pure S-Cs or pure S-Co or both, 1 uses mixed S-Cs and X-ray and 8 use various X-ray spectra. Figure 1. View largeDownload slide Dosemeters provided by the participants (Photo credit PTB). Figure 1. View largeDownload slide Dosemeters provided by the participants (Photo credit PTB). In total, these 22 IMS deliver around 30 000 eye lens dosemeters per year. Irradiation conditions Tables 1 and 2 summarize the irradiation conditions for photon and beta qualities, respectively. The chosen radiation qualities were S-Cs and N-100 defined in ISO 4037-1 standard(6), RQR6 defined in IEC 61267 standard(7) and beta radiation field series defined in ISO 6980-1 standard(8). The irradiations were performed on a cylindrical head phantom (20 cm × 20 cm)(9) developed during the ORAMED European project(5) and mentioned in ISO 15382(10) as well as in the current draft (DIS) of ISO 4037-3(11). Conversion coefficients to relate air kerma to Hp(3) were taken from Behrens(12) for ISO 4037 qualities, from Principi et al.(13) for IEC 61267 qualities and from Behrens et al.(14, 15) for beta radiation qualities. Two dosemeters of each participant were irradiated for each setup. The irradiations were carried out at PTB (Germany) and NIOM (Poland) calibration laboratories. Table 1. Irradiation plan for photon qualities. Radiation quality and angle of incidence Mean energy (keV) Dose range Hp(3) (mSv) RQR6; 0° 44 2.0–3.0 RQR6; 45° 44 2.0–3.0 RQR6; 75° 44 2.0–3.0 N-100; 0° 85 2.0–3.0 S-Cs; 0° 662 2.0–3.0 S-Cs; 60° 662 2.0–3.0 Radiation quality and angle of incidence Mean energy (keV) Dose range Hp(3) (mSv) RQR6; 0° 44 2.0–3.0 RQR6; 45° 44 2.0–3.0 RQR6; 75° 44 2.0–3.0 N-100; 0° 85 2.0–3.0 S-Cs; 0° 662 2.0–3.0 S-Cs; 60° 662 2.0–3.0 Table 1. Irradiation plan for photon qualities. Radiation quality and angle of incidence Mean energy (keV) Dose range Hp(3) (mSv) RQR6; 0° 44 2.0–3.0 RQR6; 45° 44 2.0–3.0 RQR6; 75° 44 2.0–3.0 N-100; 0° 85 2.0–3.0 S-Cs; 0° 662 2.0–3.0 S-Cs; 60° 662 2.0–3.0 Radiation quality and angle of incidence Mean energy (keV) Dose range Hp(3) (mSv) RQR6; 0° 44 2.0–3.0 RQR6; 45° 44 2.0–3.0 RQR6; 75° 44 2.0–3.0 N-100; 0° 85 2.0–3.0 S-Cs; 0° 662 2.0–3.0 S-Cs; 60° 662 2.0–3.0 Table 2. Irradiation plan for beta qualities. Radiation quality and angle of incidence Mean energy (MeV) Dose range Hp(3) (mSv) 85Kr; 0° 0.24 0.03–0.04 90Sr+90Y; 0° 0.8 2.0–3.0 90Sr+90Y; 60° 0.8 2.0–3.0 106Ru+106Rh; 0° 1.2 1.0–1.5 Radiation quality and angle of incidence Mean energy (MeV) Dose range Hp(3) (mSv) 85Kr; 0° 0.24 0.03–0.04 90Sr+90Y; 0° 0.8 2.0–3.0 90Sr+90Y; 60° 0.8 2.0–3.0 106Ru+106Rh; 0° 1.2 1.0–1.5 Table 2. Irradiation plan for beta qualities. Radiation quality and angle of incidence Mean energy (MeV) Dose range Hp(3) (mSv) 85Kr; 0° 0.24 0.03–0.04 90Sr+90Y; 0° 0.8 2.0–3.0 90Sr+90Y; 60° 0.8 2.0–3.0 106Ru+106Rh; 0° 1.2 1.0–1.5 Radiation quality and angle of incidence Mean energy (MeV) Dose range Hp(3) (mSv) 85Kr; 0° 0.24 0.03–0.04 90Sr+90Y; 0° 0.8 2.0–3.0 90Sr+90Y; 60° 0.8 2.0–3.0 106Ru+106Rh; 0° 1.2 1.0–1.5 Results evaluation The numerical results in this IC are reported as the dosemeter response R, where R is defined as the ratio of the value of the dose reported by the participant and corrected for transit dose, Hs, divided by the reference value, Hp(3)c, given by the irradiation laboratory. The performance limits according to the ISO 14146 standard(16), commonly known as ‘trumpet curves’, were adopted to analyze the results: 1F(1−2H0H0+Hc)≤R≤F(1+H02H0+Hc) (1) where Hc is the conventional quantity value (Hp(3)c in the present case), R is the response, F = 1.5 according to the recommendations of ICRP 75 report(17). H0, the ‘lower limit of the dose range for which the system has been approved’, was chosen equal to 0.3 mSv according to the current revision draft of ISO 14146 standard(18). RESULTS AND DISCUSSION Photon qualities Figure 2 gives a general overview of the response values R as a function of the reference doses Hc for photon qualities. It can be noticed that, globally, 90% of the results are within the trumpet curves built according to equation (1). This percentage differs with irradiations setups. Indeed, it is equal to 98% for S-Cs setups and 95% for N-100. This result is consistent with the fact that these qualities are very often used for calibration purposes by the participants. The percentage of results meeting the criteria specified by the trumpet curves decreases for lower energies setups, it is 89 and 84% for ‘RQR6; 0°’ and 45°, respectively. The lowest value is 77% for the ‘RQR6; 75°’ setup which corresponds to low energy and large angle irradiation setup. Figure 2. View largeDownload slide Summary of all reported response values R as a function of reference dose for all the participants for photon qualities. Figure 2. View largeDownload slide Summary of all reported response values R as a function of reference dose for all the participants for photon qualities. Figure 3 gives the distribution of the response values for each irradiation setup using a box plot representation showing the minimum, first quartile, median, third quartile and maximum responses. The median of responses is around 0.9 for S-Cs and N-100 qualities and around 1.2 for RQR series. Figure 3. View largeDownload slide Box plots showing the minimum, first quartile, median, third quartile and maximum responses per irradiation setup for photon qualities. Figure 3. View largeDownload slide Box plots showing the minimum, first quartile, median, third quartile and maximum responses per irradiation setup for photon qualities. Figure 4 presents the distribution of results, using box plots, for each participant in an anonymous manner. A relatively large variability is observed among participants, the median of responses ranges from 0.7 to 1.6. Among the 22 participants, 15 have results that are 100% within the limits set by the ISO 14146 standard(16) for all setups with photon qualities; three have all measurements within the trumpet curves for all photon radiation qualities except for the large angle setup ‘RQR6, 75°’; two have all measurements within the trumpet curves for all photon radiation qualities except for all low-energy setups (RQR6) and two failed in more than three irradiation setups. The difficulties noticed for large angle irradiation setups are more frequently observed for dosemeters placed in plastic bags, but this is not systematic and the difficulties occur as well for other types of dosemeters. Figure 4. View largeDownload slide Box plots showing the minimum, first quartile, median, third quartile and maximum responses for each participant for photon qualities. Figure 4. View largeDownload slide Box plots showing the minimum, first quartile, median, third quartile and maximum responses for each participant for photon qualities. These results do not show any obvious link with the beam quality used by participants for the calibration. A deeper analysis of this type cannot be carried out due to the relatively low number of participants and the variety of dosimeters used as well as the obligation to maintain the anonymity of results. The results observed in this IC for photon qualities are quite similar to the ones observed during the first IC of this type organized in 2014 by EURADOS(4). The spread of the results is slightly larger in the present IC but the median for all photon qualities is close to 1 for both IC. The same difficulties for setups with large angles are observed. Beta qualities Figure 5 gives a general overview of the response values R as a function of the reference doses HC for beta qualities. It can be noticed that only 56% of the results are within the trumpet curves built according to equation (1). This percentage differs very significantly with irradiation setups. For highest energy betas of 106Ru+106Rh, 91% of results are within the trumpet curves. However, for lower energy betas, the percentages decrease dramatically, 47% for 90Sr+90Y and 41% for 85Kr. Figure 5. View largeDownload slide Summary of all reported response values R as a function of reference dose for all the participants for beta qualities. Figure 5. View largeDownload slide Summary of all reported response values R as a function of reference dose for all the participants for beta qualities. It is important to notice that, for technical reasons (extremely long irradiation times), the conventional quantity value for 85Kr was relatively low (Hp(3) = 0.031 mSv as only photon radiation contributes to that quantity due to the rather low beta maximum energy of ~0.69 MeV). This value is below the usual reporting level and below the lower detection limit (LLD) of most IMS. Consequently, it is considered in this IC, that for the participants that, for 85Kr, provided a measurement equal or below their LLD, the response is correct. However, R could not be calculated and thus their data are not included in Figures 5 and 6. This is the case for five participants. Figure 6. View largeDownload slide Box plots showing the minimum, first quartile, median, third quartile and maximum responses per irradiation setup for beta qualities. Figure 6. View largeDownload slide Box plots showing the minimum, first quartile, median, third quartile and maximum responses per irradiation setup for beta qualities. Figure 6 gives the distribution of the response value for each irradiation setup using a box plot representation. It can be noticed that the median of responses ranges from 0.96 to 1.9 for all betas setups except for 85Kr for which large overresponses are observed with a median equal to 154. Among the 22 participants, only 1 has results that are 100% within the limits set by the ISO 14146 standard(16) for all setups with beta qualities. For 106Ru+106Rh, 20 participants are within the trumpet curves, while this number drops to 10 and 8 for 90Sr+90Y 0° and 60°, respectively. Regarding the participants with responses outside the trumpet curves for these beam qualities, no obvious link was found with the type of dosemeter, according to the information given by the participants. In the case of 85Kr, four participants are within the trumpet curves plus the five that provided data below LLD. All dosemeters providing a response within the curves for 85Kr are designed for Hp(3), except for one case. A relatively large variability is observed among participants, the median of responses ranges from 0.6 to 13.5. Figure 7 presents results using a box plot representation, excluding results for Kr-85; in this case, the median ranges from 0.6 to 9.8. Figure 7. View largeDownload slide Box plots showing the minimum, first quartile, median, third quartile and maximum responses for each participant for beta qualities excluding results for 85Kr. Participants marked with * gave results outside of the trumpet curves for 85Kr. Figure 7. View largeDownload slide Box plots showing the minimum, first quartile, median, third quartile and maximum responses for each participant for beta qualities excluding results for 85Kr. Participants marked with * gave results outside of the trumpet curves for 85Kr. In total, two participants are out of the limits for all the beta qualities, and six participants are out of the limits for 90Sr+90Y and 85Kr. For 85Kr radiation large overresponses are observed for some dosemeters. All dosemeters (except for one participant) with an over-response to 85Kr are designed for the measurement of Hp(0.07), because there is an insufficient filter in front of the detector. Indeed, 85Kr has a beta maximum energy of about 0.69 MeV, which does not contribute to the delivered Hp(3) dose, with the exception of the respective small photon contribution (514 keV). For 90Sr+90Y and 106Ru+106Rh, the overresponses are lower, because betas contribute significantly to Hp(3) compared to 85Kr. This issue was already pointed out in a similar IC performed in Germany(19). CONCLUSION EURADOS organized an IC exercise specifically dedicated for eye lens dosemeters, including tests with photon beams and, for the first time, beta fields. The main objective of this IC was to provide an updated overview of the different dosimetry systems currently available for eye lens dose monitoring. It is noticed that only one dosemeter gives a correct response for all qualities tested, i.e. for photon and beta radiation fields, this dosemeter is a TLD, placed in a plastic bag, calibrated in Hp(3). Results are globally satisfactory for photon qualities, whatever the type of dosemeters, since 90% of the results are in accordance to the ISO 14146 standard(16) requirements. For a minority of participants, some discrepancies between the results and reference doses were observed in the case of the irradiations setups characterized by large angles and/or low energies. These results are very similar to those observed in the case of the previous eye lens dosemeter IC organized by EURADOS(4), where 90% of the results were in accordance to the standard. Results for betas are less satisfactory and illustrate the difficulties in measuring beta radiation. The main observed problem was an over-estimate of Hp(3) for low beta energy. The intercomparison demonstrates that dosemeters designed for Hp(0.07) are, in general, not suitable to monitor the dose to the eye lens in case of betas because the filter placed in front of the detector is too thin. Dosemeters designed for Hp(0.07) are suitable for monitoring the eye lens dose only in pure photon radiation workplaces but not in workplaces with significant contributions of beta radiation. Dosemeters well designed for Hp(3), i.e. optimized for both photon and beta fields simultaneously are usually able to perform properly eye lens dose monitoring at all workplaces while for other dosemeters this is usually not the case. FUNDING This work was partly founded by the participants to this intercomparison and EURADOS. REFERENCES 1 Grimbergen , T. W. M. , Figel , M. , Romero , A. M. , Stadtmann , H. and McWhan , A. F. EURADOS self-sustained programme of intercomparisons for individual monitoring services . Radiat. Prot. Dosim. 144 ( 1–4 ), 266 – 274 ( 2011 ). Google Scholar CrossRef Search ADS 2 Romero , A. M. , Grimbergen , T. , McWhan , A. , Stadtmann , H. , Fantuzzi , E. , Clairand , I. , Neumaier , S. , Figel , M. and Dombrowski , H. EURADOS intercomparisons in external radiation dosimetry: similarities and differences among exercises for whole-body photon, whole-body neutron, extremity, eye-lens and passive area dosemeters . Radiat. Prot. Dosim. 170 ( 1–4 ), 82 – 85 ( 2016 ). Google Scholar CrossRef Search ADS 3 Council Directive 2013/59/Euratom of 5 December 2013 laying down basic safety standards for protection against the dangers arising from exposure to ionising radiation, and repealing Directives 89/618/Euratom, 90/641/Euratom, 96/29/Euratom, 97/43/Euratom and 2003/122/Euratom. Official Journal L-13 of 17 January 2014. 4 Clairand , I. , Ginjaume , M. , Vanhavere , F. , Carinou , E. , Daures , J. , Denoziere , M. , Silva , E. H. , Roig , M. , Principi , S. and Van Rycheghem , L. First EURADOS intercomparison exercise of eye lens dosemeters for medical applications . Radiat. Prot. Dosim. 170 ( 1–4 ), 21 – 26 ( 2016 ). Google Scholar CrossRef Search ADS 5 Vanhavere , F. et al. . ORAMED: optimization of radiation protection of medical staff. EURADOS report 2012-02, ISSN 2226-8057, ISBN 978-3-943701-01-2. Braunschweig ( 2012 ). 6 International organization for standardization . X and gamma reference radiation for calibrating dosemeters and doserate meters and for determining their response as a function of photon energy—Part 1: radiation characteristics and production methods. ISO 4037-1 (Geneva: ISO) ( 1999 ). 7 International electrotechnical commission (IEC). Medical diagnostic X-ray equipment—radiation conditions for use in the determination of characteristics. 61267 Ed. 2.0. IEC ( 2005 ). 8 International organization for standardization . Nuclear energy—reference beta-particle radiation—Part 1: methods of production. ISO 6980-1 (Geneva: ISO) ( 2006 ). 9 Gualdrini , G. et al. . A new cylindrical phantom for eye lens dosimetry development . Radiat. Meas. 46 ( 11 ), 1231 – 1234 ( 2011 ). Google Scholar CrossRef Search ADS 10 International organization for standardization . Radiological protection—procedures for monitoring the dose to the lens of the eye, the skin and the extremities. ISO 15382 (Geneva: ISO) ( 2015 ). 11 International organization for standardization . X and gamma reference radiation for calibrating dosemeters and doserate meters and for determining their response as a function of photon energy—Part 3: calibration of area and personal dosemeters and the measurement of their response as a function of energy and angle of incidence. ISO/DIS 4037-3 (Geneva: ISO) ( 2017 ). 12 Behrens , R. Air kerma to Hp(3) conversion coefficients for a new cylinder phantom for photon reference radiation qualities . Radiat. Prot. Dosim. 151 ( 3 ), 450 – 455 ( 2012 ). Google Scholar CrossRef Search ADS 13 Principi , S. , Guardiola , C. , Duch , M. A. and Ginjaume , M. Air kerma to Hp(3) conversion coefficients for IEC 61267 RQR X-ray radiation qualities: application to dose monitoring of the lens of the eye in medical diagnostics . Radiat. Prot. Dosim. 170 ( 1–4 ), 45 – 48 ( 2016 ). Google Scholar CrossRef Search ADS 14 Behrens , R. and Buchholz , G. Extensions to the Beta Secondary Standard BSS 2 . J. Instrum. 6 , P11007 ( 2011 ) and Erratum: J. Instrum. 7, E04001 (2012) and Addendum: J. Instrum7, A05001 (2012). Google Scholar CrossRef Search ADS 15 Behrens , R. Correction factors for the ISO rod phantom, a cylinder phantom, and the ICRU sphere for reference beta radiation fields of the BSS 2 . J. Instrum. 10 , P03014 ( 2015 ). Google Scholar CrossRef Search ADS 16 International organization for standardization . Radiation protection—criteria and performance limits for the periodic evaluation of processors of personal dosemeters for X and gamma radiation. ISO 14146 (Geneva: ISO) ( 2000 ). 17 International commission on radiological protection . General principles for the radiation protection of workers. ICRP publication 75. Ann. ICRP 27(1). Pergamon ( 1997 ). 18 ISO/FDIS 14146:2018(E). Radiological protection—criteria and performance limits for the periodic evaluation of dosimetry services. 19 Behrens , R. , Hupe , O. , Busch , F. , Denk , J. , Engelhardt , J. , Günther , K. , Hödlmoser , H. , Jordan , M. and Strohmaier , J. Intercomparison of eye lens dosemeters . Radiat. Prot. Dosim. 174 ( 1 ), 6 – 12 ( 2017 ). © The Author(s) 2018. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)

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Radiation Protection DosimetryOxford University Press

Published: May 4, 2018

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