Variation of Occupational Doses among Subspecialties in Diagnostic Radiology. A.N. Al-Haj, C.S. Lagarde, A.M. Lobriguito

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1 Variation of Occupational Doses among Subspecialties in Diagnostic Radiology A.N. Al-Haj, C.S. Lagarde, A.M. Lobriguito Biomedical Physics Department, MBC 03 King Faisal Specialist Hospital and Research Center P.O. Box 3354, Riyadh 11211, Kingdom of Saudi Arabia Abstract. In this paper, variations in occupational dose among six identified subgroups in diagnostic radiology, namely, computed tomography (CT) technologists, general radiographers, fluoroscopy technologists, radiologists, nurses and radiologic technology interns, are investigated. The dose distribution, collective dose and mean annual dose during a 5-y period ( ) are presented. More than 80% of CT technologists and general radiographers do not have measurable exposure. The combined collective dose in CT and general radiography is less than 5% of the total collective dose in diagnostic radiology while 95% of radiological workload is attributed to these two imaging modalities. Fluoroscopy and interventional radiology on the other hand, account for more than 90% of the annual collective dose. The mean annual dose of diagnostic radiology staff during this 5-y period is in the range of msv (all monitored workers) and msv (measurably exposed workers). 1. Introduction Diagnostic x-ray is the most widely used medical application of ionizing radiation. At King Faisal Specialist Hospital & Research Center (KFSH&RC), a large tertiary care medical facility in Riyadh, Saudi Arabia, over 170,000 diagnostic radiological procedures are performed annually. More than 85% of these procedures involve general radiography, 10% CT and less than 5% fluoroscopy and interventional radiology. Diagnostic radiology staff accounts for about 25% of the more than 500 classified radiation workers at KFSH&RC. Previous study had shown that the mean annual dose, averaged over 5-y periods of this occupational category at KFSH&RC ranged from 0.51 to 0.80 msv in [1]. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) reports that the worldwide mean annual dose in diagnostic radiology during the period are 0.57 msv for all monitored workers and 1.34 msv for measurably exposed workers [2]. Advances in imaging technologies as well as the development of complex radiological procedures have lead to greater specialization in diagnostic radiology. Technologists are generally assigned to perform specific imaging modalities such as general radiography, CT and fluoroscopy. This has resulted to wide variation in occupational doses among technologists and other specialists in diagnostic radiology. Analysis of occupational doses is an important component of institutional radiation protection programs. Appropriation of radiation protection resources should take into account dose variation among various occupational groups. Highly exposed groups should be appropriated more resources in terms of training, provision of protective devices and implementation of dose reduction schemes. Trends in the mean annual dose, collective dose and dose distribution can be used as indicators of good institutional radiation safety practices. In the process of optimization of protection, dose investigation levels are set by institutional management to detect deterioration in radiation safety practices [3]. To be effective, values of dose investigation levels should be set based on the expected doses for a particular practice or occupational category. In diagnostic radiology, it would not be appropriate to establish a single dose investigation value for all categories of workers. Technologists performing interventional procedures are expected to have a higher dose investigation level than those merely involved in general radiography. 1

2 This study was designed to analyze individual annual dose records of diagnostic radiology staff at KFSH&RC for the last 5 y ( ). Diagnostic radiology staff was categorized into six occupational subgroups, namely, CT technologists, general radiographers, fluoroscopy technologists, radiologists, nurses and radiologic technology (RT) interns. The dose distribution, annual collective dose and mean annual dose for each subgroup are presented and analyzed. Statistical analyses are expected to generate information useful to the management of the hospital s radiation safety program. Conclusions drawn from this study may also be of general interest to other medical institutions and radiation safety practitioners. 2. Materials and Methods An in-house dosimetry service provides thermoluminescent dosimetry (TLD) badges to radiation workers at KFSH&RC on either monthly or quarterly frequency. The TLD badge consists of the standard Harshaw (Thermo Electron Corporation, 6801 Cochran Road, Solon, Ohio 44139, USA) two-element TLD-100 (LiF:Mg,Ti) card and holder type 8814 with appropriate filters for measurement of the personal dose equivalents at depths of 10 mm [Hp(10)] and 0.07 mm [Hp(0.07)]. The TLD cards are read-out on a Harshaw 6600 automated TLD reader. Dose assessment, dosimetry report generation and the subsequent electronic storage of dose records are accomplished in the KFSH&RC Personnel Dosimetry Information System (PDIS). The PDIS is a hospital-developed database program which links dose record keeping to the labeling and issuing of dosimeters. TLD card labels, which include a bar-coded unique number, the wearer s name and institution, are generated by the PDIS. Personnel dose records from 1984 to the present are stored electronically in the PDIS. The KFSH&RC dosimetry service currently provides routine monitoring to more than 2,000 radiation workers throughout Saudi Arabia. For staff in diagnostic radiology, a single TLD badge is issued on a monthly frequency and if protective lead apron is used, the badge is worn outside the apron at collar level. Though the evaluated Hp(10) value grossly overestimates the effective dose, it is entered as the dose of record without any corrections, as a matter of policy. There is currently no specific regulations in Saudi Arabia which addresses the issue of how monitoring should be done for workers wearing protective aprons. This has resulted to different practices among institutions in the country. Ideally, workers wearing protective aprons should be issued two dosimeters, one outside the apron at collar level and the other inside the apron at waist level. The effective dose is then estimated from the readings of these two dosimeters using the Webster formula [4]. Previous experiences however had shown the difficulty of issuing multiple TLD badges as there were instances of badges being interchanged (despite color-coding), which render the interpretation of dose results meaningless. Several international recommendations suggest the wearing of dosimeter under the apron to give a better estimate of effective dose. However, this will not give an indication of the dose to the head, particularly the eyes, which might be critical for examinations involving long fluoroscopy time such as interventional procedures. The U.S. National Council on Radiation Protection and Measurements (NCRP) recommends that the evaluated Hp(10) value of outside-the-apron-over-collar dosimeter should be divided by 21 to obtain a conservatively high estimate of effective dose [5]. Pregnant workers are issued a supplementary badge, worn inside the apron at waist level, to monitor the dose to the fetus. The dose recording level is set to 0.1 msv; calculated doses below this are entered as M (minimal). For calculation purposes, M takes the value of zero. The PDIS calculates the year-to-date dose, which is the sum of the doses from January up to the current month of a particular year. Thus, the year-to-date dose for December represents the individual s annual dose. TLD badge readings, which are found to be non-occupational are removed from the employee s dose records. The average of the three previous dose records is entered as the notional dose. In this study, annual dose records of diagnostic radiology staff from were retrieved from the PDIS and exported to Excel 2000 (Microsoft Corp., Redmond, WA, USA) for analysis. The number of monitored and measurably exposed workers for each of the six previously mentioned 2

3 subgroups are presented; as well as the dose distribution, annual collective dose and the mean annual dose. 3. Results and Discussion Six hundred twenty six (626) annual dose records from diagnostic radiology during the past 5 y ( ) are included in this study. The percentage distribution is as follows: general radiographers (35%), CT technologists (17%), radiologists (15%), nurses (14%), RT interns (12%) and fluoroscopy technologists (7%). The number of monitored workers (Table I) rose from 106 in 1998 to 149 in Majority of these workers are general radiographers, the number of which increased from 40 in 1998 to 53 in Only about 11-20% of monitored general radiographers have measurable exposures ( >0.1 msv). The number of CT technologists remained constant during this 5- y period but the percentage of measurably exposed workers varied from 4-26%. On the other hand, the percentage of fluoroscopy technologists with measurable dose was about %; radiologists, 22-67%; nurses, 69-84% and RT interns, 43-86%. Table I. Number of workers monitored/measurably exposed in diagnostic radiology. Subgroup Number of workers CT technologists 23/6 23/4 23/3 23/1 21/3 General radiographers 40/8 42/5 41/8 47/6 53/6 Fluoroscopy technologists 9/8 9/8 6/6 9/6 9/6 Radiologists 9/2 15/5 18/12 22/8 27/16 Nurses 13/9 17/13 16/13 19/16 20/16 RT interns 12/6 21/9 7/6 13/7 19/11 All subgroups 106/39 127/44 111/48 133/44 149/58 The dose distribution of the 626 annual dose records (Fig. 1) is very skewed, about 63% do not have measurable doses while only 1% have annual doses >10 msv. The highest annual individual dose recorded during this 5-y period was 24.1 msv received by an interventional radiologist. This is however, an over-collar dose and using NCRP s recommendation, the calculated effective dose is about 1.2 msv. The current occupational dose limit in Saudi Arabia is 20 msv per year averaged over Percent of Annual Dose Records < <1 1 - <5 5 - < < >20 Annual Dose Range (msv) FIG. 1. Dose distribution of annual dose records from

4 defined periods of 5 y [6], as adopted from the International Commission on Radiological Protection (ICRP) recommendations [7]. The highest annual individual doses recorded for each subgroup during this 5-y period are as follow: CT technologists, msv; general radiographers, msv; fluoroscopy technologists, msv; radiologists, msv; nurses, msv and RT interns, msv. Table II shows the annual collective dose of each subgroup and its percentage contribution to the total annual collective dose in diagnostic radiology from The combined annual collective dose of CT and general radiography from is in the range of person-msv, which represents less than 5% of the total annual collective dose in diagnostic radiology. CT technologists and general radiographers constitute about 50% of the staff in diagnostic radiology. More than 95% of the annual patient workload in diagnostic radiology is attributed to these two imaging modalities. The low collective dose suggests that these two imaging modalities have reached a certain level of optimized protection such that occupational radiation risks may no longer be significant. During routine work, CT technologists and general radiographers are normally inside the control booth and are shielded from scatter radiation from the patient. The low annual collective dose demonstrates the adequacy of structural shielding in these facilities. Table II. Annual collective dose and % contribution of subgroups in diagnostic radiology. Collective dose (person-msv) Subgroup CT technologists 3 (4%) 0.6 (1%) 0.6 (1%) 0.3 (<1%) 1 (<1%) General radiographers 6.4 (10%) 1.6 (3%) 3.5 (3%) 1.7 (1%) 2.5 (2%) Fluoroscopy technologists 19.7 (30%) 12.9 (21%) 18.5 (17%) 21.2 (19%) 22 (20%) Radiologists 16.4 (25%) 17.5 (29%) 36.6 (35%) 40.3 (35%) 39.6 (37%) Nurses 18.1 (27%) 23.3 (38%) 41.5 (40%) 44.1 (39%) 35.9 (33%) RT interns 2.4 (4%) 4.6 (8%) 4 (4%) 5.3 (5%) 7.6 (7%) All subgroups 66 (100%) 60.5 (100%) (100%) (100%) (100%) Fluoroscopy and interventional radiology on the other hand, contribute about 90% of the annual collective dose, which is shared among radiologists (25-36%), nurses (27-40%) and technologists (19-30%). Radiologists generally receive the highest doses in interventional radiology. The dose to the radiologist at neck level during interventional procedure is estimated to be about twice that of the nurse and about three times that of the technologist [8]. The relatively low collective dose of radiologists at KFSH&RC might be due to some doses being missed due to non-use or erratic use of the TLD badge. The average return rate of TLD badge among radiologists is low (60%) compared to nurses (83%) and technologists (94%). Nurses at KFSH&RC are also involved in the injection of contrast media during paediatric CT examination, which requires them to be inside the CT room during part of the scan. It has been estimated that the dose to the head region of nurses during paediatric CT examination is about 0.05 msv per procedure [9]. The mean annual dose of all diagnostic radiology staff during , is in the range of msv (all monitored workers) and msv (measurably exposed workers) (Table III). The mean annual dose of the nursing staff is comparable to that of the technologists involved in fluoroscopy and interventional radiology. More than 50% of radiologists are involved only in the interpretation of radiographs and do not receive occupational radiation exposures. This explains the relatively low mean annual dose for all monitored radiologists, which is in the range of msv during this 5- y period. The mean annual dose for all measurably exposed radiologists on the other hand, is in the range of msv. 4

5 Table III. Mean annual dose of all monitored/measurably exposed workers in diagnostic radiology. Subgroup Mean annual dose (msv) CT technologists 0.13/ / / / /0.33 General radiographers 0.16/ / / / /0.42 Fluoroscopy technologists 2.19/ / / / /3.67 Radiologists 1.82/ / / / /2.48 Nurses 1.39/ / / / /2.24 RT interns 0.20/ / / / /0.69 All subgroups 0.62/ / / / / Conclusion Variations in occupational doses during a 5-y period among six identified subgroups in diagnostic radiology at a large medical center with over 170,000 radiological procedures annually, are presented. Dose distribution is skewed, 63% of diagnostic radiology workers do not have measurable exposure while only 1% have occupational doses >10 msv. More than 80% of CT technologists and general radiographers do not have measurable exposure. General radiography and CT contribute less than 5% of the total annual collective dose, while 95% of radiological workload is attributed to these two imaging modalities. The low occupational doses in general radiography and CT suggest that these two imaging modalities have reached a certain level of optimized protection, such that occupational radiation risks may no longer be significant. The low occupational doses also demonstrate the adequacy of structural radiation shielding in these facilities. Shifting these two subgroups from monthly monitoring frequency to quarterly will result to a 30% reduction in the annual cost of personal monitoring in diagnostic radiology. Fluoroscopy and interventional procedures contribute about 90% of the annual collective dose in diagnostic radiology, which is shared among radiologists (25-36%), technologists (19-30%) and nurses (27-40%). Majority of technologists and nurses involved in interventional procedures have annual over-collar doses in the range of 1-5 msv.the highest annual over-collar dose received by an interventional radiologist during this 5-y period was 24.1 msv. The calculated effective dose was 1.2 msv, which is substantially lower than the current dose limit. The dose to the head region, particularly the eyes, however, might be critical for procedures involving long fluoroscopy time. Nurses receive occupational doses, which are comparable, if not higher that those of technologists. By education, nurses do not generally receive extensive training in radiation protection and safety compared to radiologists and technologists. The low TLD badge-return rate among radiologists may suggest that some occupational doses are not being recorded. The emergence of recent imaging technologies and complex radiological procedures, such as CT- PET, CT-fluoroscopy and CT fluoroscopy-guided interventional procedures, is expected to alter the occupational dose characteristics in diagnostic radiology. Continued analysis of occupational doses should be an integral component of institutional radiation safety programs. 5. References [1] Al-Haj, A.N., Lagarde, C.S., Statistical analysis of historical occupational dose records at a large medical center. Health Phys., 83: , (2002). [2] United Nations Scientific Committee on the Effects of Atomic Radiation, Sources and Effects of Ionizing Radiation, Vol. 1: Sources. UNSCEAR Report, UN Press, New York (2000). 5

6 [3] International Commission on Radiological Protection, General Principles for the Protection of Workers. ICRP Publication 75, Pergamon Press, Oxford (1997). [4] Webster, E.W., EDE for exposure with protective aprons. Health Phys., 56: , (1989). [5] National Council for Radiation Protection and Measurements, Use of Personal Monitors to Estimate Effective Dose Equivalent and Effective Dose to Workers for External Exposure to Low-LET Radiation. NCRP Report no. 122, Bethesda, Md., (1995). [6] King Abdulaziz City for Science and Technology, Saudi Arabian National Regulations for Radiation Protection. KACST Publication, Riyadh, Saudi Arabia, (1995). [7] International Commission on Radiological Protection, 1990 Recommendations of the International Commission on Radiological Protection. ICRP Publication 60, Pergamon Press, Oxford, (1990). [8] Perna, L., Novario, R., Conte, L., Personnel doses during haemodynamic examination. Radiat Prot Dosim., 88: , (2000). [9] Al-Haj, A.N., Lobriguito, A.M., Lagarde, C.S., Occupational doses during the injection of contrast media in paediatric CT procedures. Radiat Prot Dosim., 103: , (2003). 6

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