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  • 1. The British Journal of Radiology, 79 (2006), 383–388 Occupational radiation doses in interventional cardiology: a 15-year follow-up 1,2 1 1,2 3 ˜ E VANO, PhD, L GONZALEZ, PhD, J M FERNANDEZ, BSc, F ALFONSO, PhD, MD and 3C MACAYA, PhD, MD 1 Department of Radiology, Complutense University Medical School 28040 Madrid, Spain, 2San Carlos University Hospital, Medical Physics Service and 3Cardiovascular Institute, 28040 Madrid, Spain ABSTRACT. This report describes occupational radiation doses of interventional cardiologists over 15 years and assesses action undertaken to optimize radiation protection. Personal dosimetry records of nine staff cardiologists and eight interventional cardiology fellows were recorded using personal dosemeters worn over and under their lead aprons. The hospital in which this study was conducted currently performs 5000 cardiology procedures per year. The hospital has improved its facilities since 1989, when it had two old-fashioned theatres, to include four rooms with more advanced and safer equipment. Intensive radiation protection training was also implemented since 1989. Initially, some individual dose values in the range of 100– 300 mSv month21, which risked exceeding some regulatory dose limits, were measured over the lead apron. Several doses in the range of 5–11 mSv month21 were recorded under the apron (mean510.2 mSv year21). During the last 5 years of the study, after the implementation of the radiation protection actions and a programme of patient-dose optimization, the mean dose under the apron was reduced to 1.2 mSv year21. Current mean occupational doses recorded under the lead apron are 14% of those recorded Received 11 May 2005 during 1989–1992 and those recorded over the apron are 14-fold less than those Revised 1 August 2005 recorded during 1989–1992. The regulatory dose limits and the threshold for lens Accepted 1 September injuries might have been exceeded if radiation protection facilities had not been used 2005 systematically. The most effective actions involved in reducing the radiation risk were DOI: 10.1259/bjr/26829723 training in radiation protection, a programme of patient-dose reduction and the systematic use of radiation protection facilities, specifically ceiling-suspended ’ 2006 The British Institute of protective screens. Radiology Radiation exposure is a significant concern for inter- Several aspects of radiation safety in the practice of ventional cardiologists (ICs) because workloads and the cardiology have been addressed by the American complexity of procedures have increased over the past College of Cardiology in a consensus document [4]. few years without a corresponding increase in the The UNSCEAR 2000 report [5] states that fluoroscopic number of specialists [1]. Although reduced scatter procedures are by far the largest source of occupational radiation in catheterization laboratories compared with exposure in medicine. Cardiac catheterization, in parti- that in old X-ray system laboratories, improved radio- cular, can represent a major source of exposure. A study logical protection facilities, and better, more inclusive performed in the UK [6] indicated that ICs receive a radiation protection training for ICs have substantially mean annual dose of 0.4 mSv, twice that received by reduced the risk of radiation exposure, the complexity radiologists and many times that received by nurses and and number of procedures have increased. Therefore, technicians. interventional cardiology is recognized as a high-radia- There are substantial differences in occupational doses tion-risk practice [1–3], and evaluation and follow-up of between cardiac laboratories [7–10]. This is caused by occupational doses should be considered an important differences in X-ray systems (old film-based systems part of quality assurance (QA) programmes. versus digital units) and their particular settings, levels of training in radiation protection, frequency of use of Address correspondence to: Prof. Luciano Gonzalez. radiation protection facilities and personal dosemeters, This study was partially funded by the European Commission 5th and workloads of specialists. Framework Programme, Contract DIMOND FIGM-CT-2000-00061, Renaud et al [11] described a 5-year follow-up of the the Spanish Department for Science and Technology (project radiation doses received by the in-room personnel of BFI2003-09434) and the Spanish Nuclear Safety Council. three cardiac catheterization laboratories and concluded Validation of some results with TLD chips was carried out with experimental equipment partially funded with EC FEDER that some workers may have exceeded the occupational resources. limit for the lens of the eye. Lens injuries have been The British Journal of Radiology, May 2006 383
  • 2. E Vano, L Gonzalez, J M Fernandez et al ˜ reported for several interventional radiology suites in An interactive CD-ROM, co-sponsored by the which radiation protection conditions were not appro- European Commission [17], is used to provide radiation priate to the level of risk [12]. protection training for residents and fellows who This report describes occupational radiation doses commence work in interventional suites during the from interventional cardiology in a university hospital intervals between radiation-protection training courses. over a period of 15 years and the actions that were taken A copy of this CD-ROM is given to all new doctors on to optimize radiation protection. Data were gathered commencement of duty at the hospital’s interventional from a dosemeter worn on the trunk of the body under cardiology service. In addition, refresher sessions on the apron and a dosemeter worn outside the apron, as radiation protection are presented periodically. recommended by the International Commission on Detailed analysis of personal dosimetry records of IC Radiological Protection (ICRP) [1]. personnel is conducted every month. This is followed by individual interviews with persons exposed to monthly doses greater than 1.0 mSv under the apron (1/20 of the Methods and materials annual effective dose limit) or greater than 7.5 mSv over the apron (1/20 of the annual lens dose limit). In addition, Follow-up of IC’s personal dosimetry records was a progressive audit programme was implemented to performed in a university hospital currently performing detect high patient doses, facilitate clinical follow-up in more than 5000 procedures per year in four catheteriza- cases of likely skin radiation injury and to implement tion laboratories with nine staff cardiologists and eight corrective action when necessary. Since 1999, a national fellows. In 1989, this interventional cardiology service standard [15] stipulates that patient doses in interventional used two old-fashioned X-ray units. In 1994, a Philips procedures must be estimated and recorded. Because this Optimus M-200 Poly C X-ray unit (Philips, Best, The patient-dose audit has reduced patient doses, occupational Netherlands), installed in 1988, was upgraded and an old doses have also been reduced [2]. CGR unit was exchanged for a Philips Integris HM-3000. Personal dosimetry services typically provide monthly In 2000, two new Philips Integris H-5000 units were estimates of Hp(10) (the dose equivalent in soft tissue at installed. All systems now have protective screens 10 mm depth), which is usually compared with the suspended from the ceiling. This radiation protection annual limit of effective dose and with the eye lens limit tool, which had previously not been installed in one of [18], and Hp(0.07) (the dose equivalent in soft tissue at the rooms, was not used regularly by all specialists until 0.07 mm depth) [18]. Usually, no significant differences they were made aware of its importance. In addition, between values are found in cardiac catheterization lead aprons, thyroid protectors and lead glasses were suites. The values reported in this paper are for estimates also available and are used routinely at present (with a of Hp(10) obtained from personal dosimetry readings. few exceptions). The effective dose, E, can be estimated [13] from the Two personal dosemeters with thermoluminescent dosemeter values for Hw (under the apron at the waist, dosimetry chips, as recommended by the radiation although this position is not critical) and Hn (above the protection service of the hospital, were used for occupa- apron at the neck) from the equation: tional dosimetry: one was worn on the trunk of the body under the apron and the other was worn outside the E~0:5Hw z0:025Hn apron at the level of the collar or the left shoulder. A dosemeter under the apron provides an estimate of the dose to the organs of the shielded region. A dosemeter NCRP report 122 [13] contains specific recommenda- worn outside the apron supplies an estimate of the dose tions for calculating the effective dose when protective to the organs of the head and neck, including the thyroid aprons are worn during diagnostic and interventional and lenses of the eyes (if unshielded), but greatly medical procedures involving fluoroscopy. In addition to overestimates the doses to organs of the trunk. Results the above formula, it states that the effective dose can be obtained from both dosemeters were used to estimate the estimated as Hn/21 if only one dosemeter is worn on the occupational effective dose as recommended by the neck outside the apron. NCRP [13] and ICRP [1]. Dosemeters were read monthly by a public dosimetry service accredited and audited by the National Regulatory Authority. Results Before 1992, training in radiation protection for ICs was scant, if performed at all. Subsequently, a radiation The data from occupational dosimetry were allocated protection training programme was initiated in accordance to one of three periods for purposes of analysis. with national regulations [14]. Of the staff cardiologists working in the centre, 90% attended the courses and were accredited in radiation protection, as required by the First period (1989–1992): investigation of high dose National Regulatory Authority. Some new cardiologists, values and implementation of a customized especially fellows, did not attend the courses. New radiation protection programme regulations in force since 1999 [15] require a second level of radiation protection training for interventionalists, Table 1 shows the findings from this period. Most which includes training in radiation protection of patients values were in the range of 100–300 mSv month21, but in and QA, as recommended by the ICRP [1]. Training in one case a dose of 1600 mSv month21 was recorded by radiation protection of patients is also required by the left shoulder dosemeter outside the lead apron. European Directive 43/97/EURATOM [16]. Values in the range of 5–11 mSv month21 were recorded 384 The British Journal of Radiology, May 2006
  • 3. Occupational radiation doses in IC Table 1. Individual monthly high values of personal dose equivalent Hp(10) and total Hp(10) values under apron during the year (except for cases indicated in the footnotes). Capital letters and numbers in the staff column are an internal code allowing traceability of the reported data Staff member Year Max. mSv/month Total Hp(10) (under apron) (mSv) I1 Senior cardiologist 1989 51 (over apron) 7.4 B1 Senior cardiologist 1989 8 (under apron) 27.8a F1 Senior cardiologist 1989 4.6 (under apron) 12.3 G1 Senior cardiologist 1990 62 (over apron) 5.2 R1 Senior cardiologist 1990 65 (over apron) 9.2 G1 Senior cardiologist 1991 346 (over apron) 27 G1 Senior cardiologist 1992 180 (over apron) 4.2 A1 Senior cardiologist 1992 155 (over apron) 7.1 F2 Senior cardiologist 1992 54 (over apron) 23.7 R1 Fellow cardiologist 1992 1640 (over apron) 47b B1 Fellow cardiologist 1992 185 (over apron) 3.1c C1 Resident 1992 179 (over apron) 11 a Values over apron not available. Incorrect use of the dosemeter cannot be excluded. b Value under apron during the month receiving 1640 mSv over the apron. 47 mSv are 2.9% of the dose over the apron. Abnormal irradiation of the over-apron dosemeter was not demonstrated. c Only some months. under the apron. An initial complete evaluation of the initiative, patient dose values were measured, recorded radiation protection conditions of the catheterization in a database and analysed periodically. laboratories was done, after which follow-up of abnor- Since 2000, the MARTIR training CD-ROM [17] has been mal values was investigated and corrective actions distributed to new personnel joining the interventional proposed. Consequently, the occupational medical ser- cardiology service, and radiation protection refresher vice of the hospital advised some staff to abstain from seminars are held two or three times per year. Individual catheterization duties for several months. The National real-time occupational dosimetry has also been implemen- Regulatory Authority was informed of these actions. ted for some procedures. Electronic dosemeters (Unfors Lens injuries would have occurred in those situations if EED-30; www.unfors.se) measure the dose accumulated the corrective actions had not been put into practice by the specialist throughout a procedure and the max- immediately. imum dose rate, which provides information about the correct use of the protective screen. Maximum values recorded by dosemeters placed over Second period (1993–1998): consolidation of the the apron were lower during the third period than radiation protection programme during the second period and ranged between 3 mSv month21 and 4 mSv month21. The maximum Training courses in radiation protection and seminars dose under the apron was generally 2 mSv month21, but with ICs (including fellows) were commenced, new X- some abnormally high values were recorded for specia- ray systems with radiation protection facilities were lists doing electrophysiology cardiac procedures (in installed, and a formal programme of quality control service since 2000). A maximum over-the-apron dose of (QC) and strategies to reduce patient and staff doses 26 mSv month21 was recorded for one specialist. were launched. Maximum monthly dose values (over the The workloads during the three periods were similar: apron) ranged from 7 mSv to 10 mSv, with the exception five to six procedures per day and room, shared between of a new fellow, for whom high readings of up to one to three cardiologists. Some of the fellows stayed at 28 mSv month21 were recorded on two occasions. The the hospital for short periods and often performed many highest yearly Hp(10) values under the apron were procedures per day to improve their skills. Typical between 2 mSv and 3 mSv. workloads were two to four procedures per day for staff and three to six procedures per day for fellows. Table 2 shows monthly doses before, during and after radiation Third period (1999–2004): implementation of protection training. Mean and median doses decreased occupational radiation protection in the QA significantly after the training courses. programme Unpaired t-test analysis revealed statistically signifi- cant differences between means for doses before and During this period, the frequency of the X-ray system after the training periods. In two-tailed tests, p-values QC programme increased from once yearly to two or were less than 0.05 (p50.01 for 1996 vs 1991; p50.02 for three times per year. The old CGR X-ray system was 1995 vs 1992). Table 3 presents the annual dose values for removed in 1999. Full characterization was done by the three periods. Only personal dosimetry records measuring patient entrance dose, image quality and comprising all the monthly dose values were used. scatter radiation levels for all fluoroscopy and cine Data in which background dose values were recorded by modes. Closer contact with the maintenance engineers the over-apron dosemeter of specialists who had a was established to customize the operation modes to substantial workload were excluded from the analysis, fulfil the image quality requirements of the cardiologists as this indicated that the personal dosemeter had not while keeping doses as low as possible. Since this been used. Between 20% and 30% of the cardiologists The British Journal of Radiology, May 2006 385
  • 4. E Vano, L Gonzalez, J M Fernandez et al ˜ Table 2. Relevant dose values (in mSv/month) under the lead apron, before, during and after the training courses on RP for numbers of IC specialists indicated Year Sample Range Mean¡SD Median 1991 8 1.9–26.5 9.0¡9.3 5.1 1992 11 0.9–24.2 7.4¡8.5 3.7 1993 (training) 7 1.0–4.4 1.9¡1.0 1.6 1994 (training) 12 0.6–13.0 3.0¡3.3 1.6 1995 10 0.7–4.1 1.8¡1.2 1.3 1996 13 0.4–5.8 1.5¡1.6 0.9 neglected to send their personal dosemeters to the reported during the years 1989–1992 are real dose values dosimetry service for processing every month. or incidental readings caused by inappropriate use of the Differences between under-apron doses during 1989– dosemeters. In fact, the bulk of the results in Table 1 should 1992 and the other two periods were statistically correspond to real dose values received by the cardiolo- significant (p,0.01), and a more significant difference gists during a period in which there was no culture of was noted for values over the apron (p,0.004). safety: ceiling-suspended screens were absent or unused, Table 4 presents estimates of the transmitted fraction the X-ray systems were used in relatively high-dose of energy across different lead aprons with thickness fluoroscopy modes and film cine acquisition was done at equivalents in the range of 0.25–0.5 mm lead. The IPEM 25 frames s21. The high dose values shown in Table 1 software application [19] for spectra from 70 kVp to cannot be considered a consequence of the incorrect use of 90 kVp was used for calculations. the dosemeters. All abnormal doses were reported to the The real spectra of scattered radiation in the catheteri- doctors wearing the dosemeters and investigated with zation rooms are difficult to determine. However, the X- them, and no reason was found to suggest that incidental ray beam used for interventional cardiology in our dosemeter irradiation occurred. laboratories (with the Philips Integris systems) typically For the 1640 mSv measured at the left shoulder of a ranges between 80 kVp and 110 kVp. Thus, the energy visiting cardiologist in 1 month, it was not possible to degradation in the scattering process would yield dose- prove any abnormal dosemeter irradiation. The dose transmitted fractions of between 3.3% and 8.3% measured by the dosemeter worn under the apron was for 0.25 mm lead aprons, between 1.5% and 4.9% for 42 mSv in that month, 2.8% of the dose over the apron. 0.35 mm lead aprons, and between 0.5% and 2.4% for This figure is compatible with the transmitted fraction 0.5 mm lead. Thus, a dose under the apron of between across the lead apron (Table 4). Moreover, experimental 0.5% and 8.3% of the values measured over the apron measurements in one of the cardiology rooms used by a was considered compatible with the personal protection fellow simulating clinical conditions produced doses in used and was regarded as a good indicator of proper use good agreement with the dosemeter readings, taking into of personal dosemeters. The same criterion has been account the presumed work rate, fluoroscopy time and used to reject unreliable data, and the values from frame rate per procedure, and the mean scatter dose rate Tables 2 and 3 are fully compatible. for a non-pulsed fluoroscopy mode. In summary, the radiation protection programme Distance is an important factor that could increase (or during the 15-year period reduced the effective dose to decrease) the scatter dose rate. A distance of 65 cm cardiologists by one order of magnitude, avoiding cases of high individual doses. The real mean effective dose for between the cardiologist and the isocentre has been cardiologists in our centre during the last 4 years of our supposed, but a variation of 15 cm nearer to the patient study was 1.2 mSv year21, which is compatible with could increase the occupational dose by 70%. In addition, results recently reported by Delichas et al [20] (1.2– considering that the protective screens—typically 2.7 mSv/procedure, a dose of 0.7–1.5 mSv year21 for a equivalent to a shielding of 0.5–1.0 mm lead—can reduce workload of 50 procedures per month). the scatter dose by a factor of 100 if properly used, differences in the reported occupational doses in the scientific literature of two orders of magnitude measured over the lead apron are not surprising. In fact, Pratt and Discussion Shaw showed that the relationships between the cardio- Several questions arise from the results presented in this logist’s eye dose and factors such as the dose efficiency of paper. First, it should be determined if the high doses the X-ray equipment, scattered-dose rates, examination Table 3. Mean values (and standard deviation) in mSv/year of occupational doses of cardiologists during the periods referred to. The percentage of dose under apron in relation to the dose over apron is indicated in the Hp(10) ‘‘under apron’’ column between brackets Number of Period Hp(10) Effective dose Effective dose (NCRP, reliable data (NCRP, using two using over-apron over apron under apron dosemeters) dosemeter) 15 1989–1992 259¡249 10.2¡8.6 (3.9%) 11.6 12.3 24 1993–1998 31¡15 1.7¡1.1 (5.5%) 1.6 1.5 11 1999–2004 18¡7 1.4¡0.4 (7.7%) 1.2 0.86 386 The British Journal of Radiology, May 2006
  • 5. Occupational radiation doses in IC Table 4. Protection of different lead aprons for X-ray beams Conclusions filtered with 3 mm Al and generated at the kVp indicated Occupational doses measured on specialists who are kVp Protective apron Fraction of energy routinely using their personal dosemeters show that the mm lead equivalent transmitted (%) radiation protection level has significantly improved in 90 0.25 8.3 the last decade. A reduction in the effective dose by a 90 0.35 4.9 factor of 10 has been achieved. The most successful 90 0.50 2.4 action to reduce occupational doses has been training in 80 0.25 5.7 radiation protection. The use of ceiling-suspended 80 0.35 3.0 protective screens in a systematic way by the cardiolo- 80 0.50 1.3 gists and the programme of patient dose reduction were 70 0.25 3.3 important complementary actions. New X-ray equip- 70 0.35 1.5 ment also contributed to further dose reductions, but its 70 0.50 0.5 relative impact cannot be distinguished from the training effect in this study because of their interdependence. protocols and workload are complex and vary from Another significant conclusion is that mean values of the centre to centre [21]. occupational doses in catheterization laboratories could Data considered reliable are scarce in Tables 1 and 2 provide an incorrect estimate of the real radiological risk because between 1989 and 1996, a significant number of if some specialists are not using their personal dose- cardiologists did not use the personal dosemeters during meters on a regular basis. all procedures or overlooked the established procedure of sending the dosemeters to the medical physics service monthly. Compliance with the radiation badge policies is Acknowledgments one of the main problems in many interventional cardiology services. Reported occupational dose values The authors thank Mercedes Lago for her help in are often surprisingly low and the reason is not a high gathering dosimetry data. level of radiation protection, but a lack of use of personal dosemeters. McCormick et al [10] reported that after a References mandatory radiation protection training programme, 1. ICRP Publication 85. Avoidance of radiation injuries from compliance with the radiation badge policy was only medical interventional procedures. Ann ICRP. Oxford, UK: 36% in 1999, reaching 67% in 2000 and 77% in 2001 for Pergamon, Elsevier Science Ltd, 2000;30(2). physicians and nurse clinicians. Therefore, confidence in 2. Vano E. Radiation exposure to cardiologists: how it could the mean dose values determined by the regional be reduced. Heart 2003;89:1123–4. dosimetry services, and sometimes by the regulatory 3. Finkelstein MM. Is brain cancer an occupational disease of bodies, to assign occupational doses is open to discus- cardiologists? Can J Cardiol 1998;14:1385–8. sion, as stated by UNSCEAR [5]. 4. American College of Cardiology. Radiation safety in the Another important point for improving the occupa- practice of cardiology. ACC expert consensus document. J Am Coll Cardiol 1998;31:892–913. tional dosemetry data is reporting dose results from 5. United Nations Scientific Committee on the Effects of dosemeters over and under the lead apron [1, 13] and Atomic Radiation. Sources and effects of ionizing radiation. combining them to calculate a more realistic effective UNSCEAR 2000 report to the General Assembly, with dose. The over-apron dosemeter provides very useful scientific annexes. Annex E. Occupational radiation expo- information on the risk of lens injuries in interventional sures. (Available at www.unscear.org). New York: United suites. The data in Table 3 show that differences up to Nations, 2000. 15% with the conventional under-apron dose approach 6. Hughes JS, O’Riordan MC. Radiation exposure of the UK can be found when considering the proposed NCRP population—1993 review. NRPB-R263 (1993). Quoted in formula [13]. UNSCEAR 2000 report. Finally, one may wonder if occupational dose values 7. Tsapaki V, Kottou S, Vano E, Komppa T, Padovani R, Dowling A, et al. Occupational dose constraints in inter- as high as those reported for the period 1989–1993 could ventional cardiology procedures: the DIMOND approach. be reached with new X-ray systems and radiation Phys Med Biol 2004;49:997–1005. protection facilities. Fortunately, the probability is low. 8. Kuon E, Schmitt M, Dahm JB. Significant reduction of Modern interventional cardiology X-ray systems have radiation exposure to operator and staff during cardiac significantly decreased the radiation level for the patient interventions by analysis of radiation leakage and and, as a consequence, the scatter radiation level. In improved lead shielding. 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