Received 9 March 2017; revised 13 May 2017; editorial decision 15 May 2017; accepted 20 May 2017

Transcription

1 Radiation Protection Dosimetry (2018), Vol. 178, No. 1, pp Advance Access publication 17 June 2017 doi: /rpd/ncx072 A COMPARISON OF OCCUPATIONAL DOSES IN CONVENTIONAL AND INTERVENTIONAL RADIOLOGY IN IRAN Fereidoun Mianji 1, *, Fariba Gheshlaghi 2, Majid Darabi 2, Mohammad Reza Kardan 1, Mirshahram Hosseinipanah 1 and Farideh Zakeri 1 1 Nuclear Science & Technology Research Institute, End of North Kargar, Tehran, Iran 2 Iran Nuclear Regulatory Authority, End of North Kargar, Tehran, Iran *Corresponding author: fmianji@aeoi.org.ir Received 9 March 2017; revised 13 May 2017; editorial decision 15 May 2017; accepted 20 May 2017 Occupational exposures in conventional and interventional radiology were investigated over a period of 10 years for all radiation workers. The statistical analysis carried out on the refined data showed that the average annual effective doses in conventional and interventional radiology were 0.28 and 0.59 msv for measurably exposed workers and 0.18 and 0.52 msv for all monitored workers in More than 99.9 and 82.8% of radiation workers in conventional and interventional radiology received annual doses less than the public dose limit (1 msv) in Comparing the occupational dose levels of different countries (including Iran) in conventional as well as interventional radiology showed a poor comparability among them. Regarding the doses above the investigation level, the analysis showed that majority of them were due to improper use of personal dosimeters (false doses) and only 0.01 and 0.12% of the dose actually crossed the level in conventional and interventional radiology in INTRODUCTION Diagnostic medical radiation practices are divided into four groups in Iran including dental intraoral radiography, fluoroscopy, nuclear medicine and conventional radiology. In this article the term conventional radiology is used for all static imaging techniques (plain radiography, mammography, bone mineral densitometry, CT and dental extraoral radiography (panoramic and cephalometric imaging)). Fluoroscopy and other continuous or continual exposing techniques are investigated as a separate group (interventional radiology) due to the fact that the occupational exposure levels can be higher for them (1). There are reports of the necessity for more safety considerations in this group (1 3). Such reports, in the absence of national comprehensive data, may raise concerns about radiological risks in interventional and (some) conventional radiology workers. Although the internationally reported results provide very useful information for various radiation practices (4, 5), several factors may be sources of uncertainty for their application in a country like Iran whose information is not included in those reports. The main factors include variety in the type, model and age of devices that are in use, non-identical safety management and quality control issues, and differences in the safety culture of radiation workers in different countries. Diagnostic radiology using x-rays is an expanding field in medicine particularly in the developing countries (4). The number of radiologists in the USA, approximated by Harvey L. Neiman Health Policy Institute, is (6) and the number of x-ray technicians is expected to be several fold higher. Total number of radiation workers involved in medical uses ofradiationintheworldwasestimatedtobe7.4million with the collective effective dose of 3540 man Sv and the average annual effective dose of 0.5 msv according to the UNSCEAR 2008 report (4).Aconsiderable population of radiation workers is employed in conventional radiology, therefore, the largest potential contribution to the occupational dose in medical uses of radiation may be expected to arise from this category of practices. The UNSCEAR 2008 report estimated the population of this category (except dental) to be 6.74 million (~90% of the total number of monitored workers in the medical uses of radiation). The estimated collective dose for the category was 3370 man Sv (95% of the total collective dose for all medical uses). The average annual effective dose due to conventional techniques was reportedly 0.5 msv (range: msv) for the monitored workers and 1.2 msv (range: msv) for the measurably exposed workers (4). Only ~0.1% of the monitored workers in diagnostic radiology were involved in interventional procedures and their average annual effective dose was ~1.6 msv for the monitored workers and 3.1 msv for the measurably exposed workers, with a range of msv. Although many surveys on per capita average or collective occupational exposure for this category are carried out worldwide (4, 5, 7, 8),the national information for many countries is as yet, absent in the reports. It is worth mentioning that the reported global figures are estimated using the data from a handful of countries, among which the USA s data is the most influential (5). The Author Published by Oxford University Press. All rights reserved. For Permissions, please journals.permissions@oup.com

2 Radiation workers (radiologists, technicians, and assistants) are required to wear personal dosimeter in Iran (except for intraoral radiography). Personal monitoring in Iran is center-based, i.e. any radiation worker who works in more than one separately licensed center receives a separate personal dosimeter (film badge) for each of the centers that may perform different practices. However, very few radiation workers are employed in more than one center in Iran. It is therefore possible to evaluate the occupational dose situation in every practice independent of the other practices. To this end, provided that the related data over a long period are available and valid, a thorough investigation of occupational doses is the preferred approach. A study in 2015 compared the occupational doses in nuclear medicine, diagnostic radiology, and radiotherapy in Tehran city (Iran) (9). This study included interventional techniques in the diagnostic radiology, thus, the average dose level of them (which may dramatically differ) were not defined separately. Another study evaluated the necessity of personal monitoring in intraoral dental radiography based on the annual effective occupational doses (10). Apart from the mentioned reports, and a report on industrial radiography (11), the occupational exposure statistics have not been thoroughly investigated in Iran. This work verifies the national situation in conventional as well as interventional radiology and compares the results with the reported figures for other countries. The survey is based on the data of the national registry system that covers the bimonthly (every 2 months) of more than twenty thousand conventional and ~2600 interventional radiology workers over a 10-year period. Furthermore, the frequencies of overexposure cases and their reliability in both categories are assessed. MATERIALS AND METHODS The national occupational dose registry system The first dosimetry service of Iran was launched by Tehran University in 1962 with 62 persons. With the establishment of the Atomic Energy Organization of Iran (AEOI) (12), this duty was transferred to the Iran Nuclear Regulatory Authority (INRA), a department of the AEOI. Film badge and TLD personal dosimetry services were privatized in 2006 and 2012, respectively. However, the INRA continued controlling and managing the National Occupational Dose Registry system (NODR). In 1978, the total number of centers involved in all kind of practices who were under the umbrella of NODR was 545. This number increased to 1446 with 9329 radiation workers in 1989 when the Radiation Protection Act of Iran was ratified (12). By the end of 2014, the data for 3422 centers and radiation workers (using film badge) F. MIANJI ET AL. 38 including all the industrial, medical, research, etc., practices were being recorded in the NODR. The most commonly used personal dosimeter in all of the industrial and medical practices except industrial radiography (changed to TLD in 2004) and applications using neutron sources, like well logging, is film badge in Iran. It is recommended that the personal dosimeter be placed on the upper left side of chest under the lead apron (if used) (1).Forsomeinterventional procedures, if exposure to the interventionist s upper parts of body (that are uncovered by the apron) is substantial, the use of second dosimeter over the apron might be more suitable. However, to avoid incorrect implementation of the two-dosimeter system in interventional radiology, placing a single dosimeter under the apron is the adopted standard in Iran. The calculated personal dose equivalent at a depth of 10 mm (Hp(10)) is considered as the effective dose of the users. The used films are Foma Personal Monitoring Film (Foma PMF). Foma PMF consists of a high speed film (DF10) and a low speed film (DF2). Minimum detectable level (MDL) of this set is 0.05 msv. Any readings below this level are marked as an immeasurable dose. Calibration of film dosimeters is performed at the Secondary Standard Dosimetry Laboratory (SSDL) of the AEOI according to the standard calibration procedure recommended in the IAEA document (13). One extra dosimeter is sent to every radiology center as the background dosimeter in every dosimetry period. The centers are required to keep the background dosimeters in their places (far from radiation sources) over the period. The background dosimeter s reading is deducted from all the personal dosimeters that are used by the center s staff. Personal doses <0.05 msv over every monitoring period are recorded zero. However, when an individual has a <MDL film badge reading, her/his actual dose can range from zero to the MDL of the type of film utilized. For estimating individuals annual or populations collective doses, these immeasurable are considered zero by many countries, however, some other countries assume a nonzero value for them (4). The Defense Threat Reduction Agency (DTRA) proposes one-half of the MDL (0.025 msv) be considered in place of zero in calculating the cumulative or collective doses for such readings, and this conservative idea is adopted in this article too (14). Overexposure cases One of the interesting properties of the film dosimetry is that abnormal exposures to the dosimeters are recognizable in this method. Abnormalities may happen unintentionally/intentionally by the users, for instance, by putting the film in the field of primary beam of the x-ray machine or nearby radiation sources. Curiosity, checking whether the dosimeter shows the real absorbed dose, deceiving employers about the risk of

3 the practice, etc. can be reasons for so doing. This property of the film dosimetry is effectively used for correcting the personal doses and removing corrupt data from the registry system (NODR). The investigation level (IL) is the value of a quantity such as effective dose, intake or contamination per unit area or volume at or above which an investigation would be conducted (15). It is recommended to set IL to 0.3 of the annual dose limit divided by the number of measurement periods per year. For all practices including conventional and interventional radiology, the number of periods is six per year in Iran. Exceeding the IL is not a violation of the limits but a warning that requires re-evaluating the working conditions and procedures to remain in line with the ALARA concept. The effective dose IL is set to 3 msv for the measuring period (2-month) in interventional radiology. In conventional radiology however, considering the intrinsic low risk of this category it is set to the conservative level of 1 msv. The studied group At the end of 2014, 2835 out of 3422 centers and out of persons under the film badge service belonged to conventional radiology in Iran. These figures were 127 centers and 2635 radiation workers for interventional radiology. Figure 1 shows the total number of radiation workers under the film badge dosimetry service and the populations of conventional and interventional radiology radiation workers from 2005 to According to the figure, more than 73% of all radiation workers were in the category of conventional radiology and only ~9% were employed in interventional radiology in 2014 (the ratios may differ from country to country) (4). The remaining 18% includes the radiation workers in nuclear medicine and therapeutic practices in A COMPARISON OF OCCUPATIONAL DOSES medical field and all industrial and research applications of radiation sources except industrial radiography, well-logging and some nuclear facilities. In order to develop a comprehensive database, first, all the paper-based dose were transferred to the integrated computerized system (NODR) from 2008 to Although NODR is reliable enough for statistical analysis, its most comprehensive part is the recent decade s data. Hence, the data for were used for this study. For verification of unjustified dose, the period of for which such cases have been carefully investigated by the INRA, was utilized. The results defined the causes leading to true or false recorded overexposures. Method for defining false overexposures All the returned films to the service providers are controlled for false indications and unusual image patterns. The films with doses above the IL and the unusual films are systematically followed up by the INRA by sending a questionnaire to the using centers. The questionnaire must be filled in by the radiation worker first. He/she explains in the questionnaire, from his/her point of view, the reasons for such a relatively high dose (recorded by the film badge). The radiation worker is also requested to report if his/her film badge is used in another center during the same monitoring period. The licensee s radiation protection officer (RPO) adds his/her explanations and comments to the questionnaire, and then, it is endorsed by the licensee and is sent to the INRA (often with long delays). The completed questionnaires undergo the regulatory evaluation. Films with unusual patterns, according to the personal dosimetry service provider s report, are always registered as <MDL regardless of the answers given by radiation workers (unless an accidental exposure is reported). For normal films with Total # R.W. # R.W. in Conven. Radio. # R.W. in Interven. Radio # R.W Year Figure 1. Total number of radiation workers (R.W.) using film badge and the number of R.W. in conventional and interventional radiology in Iran. 39

4 doses above the IL, final decisions on reliability of the are made based on the explanations that the workers provide. For instance, in interventional radiology, if a radiation worker states that he/she has worn the badge on the lead apron (instead of under apron), his/her dose is corrected by dividing it by 21 (an estimation of the attenuating factor of typical lead aprons) (16). The investigation aims at determining whether the recorded doses are real personal occupational doses, i.e. the film was not unintentionally exposed when the badge was not being worn by the user. Moreover, determining the root causes that have led to such real or unreal occupational exposures is targeted. The latter supervisory function is necessary for improving the regulations toward optimization of the occupational exposures. The INRA s scrutiny through the questionnaires has a third purpose too. It is to encourage the radiation workers as well as the licensees to understand and thoroughly evaluate the conditions which have led them into such situations. Not all the centers answered the questionnaires in this study, therefore, the period of that is the most complete part of the follow-up program was chosen for this survey (INRA contacted the centers through telephone in this period). RESULTS AND DISCUSSIONS Tables 1 and 2 depict the statistics of the personal dosimetry over the investigated period for both categories. For each year the total number of radiation workers and dose are given. Every radiation worker is supposed to be monitored six times a year; thus, the total number of dose in each year is expected to be almost six times the corresponding number of radiation workers. However, such an exact ratio cannot be seen in the table, particularly for years The main reason is that many centers did not regularly return the used film badges. As a quantitative measure of this problem, the third column of the Table shows the rate of the returned (by user) to the sent (by service provider) films for the last period (sixth) of each year (as returning rate of the used films). The unreturned dosimeters often are returned with delay (sometimes after several months). There is no accurate figure available for explaining the ratio of the lost to the returnedwith-delay dosimeters in each year. F. MIANJI ET AL. The average annual effective doses The average annual effective doses in years for the categories included in this study were calculated by two methods. One method only considered the. It represents the 40 Table 1. The statistics of the personal dosimetry for the conventional radiology. # Annual EDs >1mSv # Records >1 msv Average annual (6 /year) ED (msv) based on Annual collective ED (man Sv) Based on # Records # R.W. with all <MDL # Dose Year # R.W. Returning rate of the used films (%) all all ED, effective dose.

5 A COMPARISON OF OCCUPATIONAL DOSES Table 2. The statistics of the personal dosimetry for interventional radiology. # Annual EDs >1 msv # Records >1 msv Average annual (6 /year) ED (msv) based on Annual collective ED (man Sv) Based on # Records # R.W. with all < MDL # Dose Year # R.W. Returning rate of the used films (%) all all ED, effective dose. average annual effective dose only for measurably exposed radiation workers. Thus, it is not a true index for the whole population. The average annual effective doses were calculated for all monitored workers as well (based on the DTRA method) and the results are depicted in separate columns of tables. As can be seen, the values are lower than the average figures reported for the world (UNSCEAR 2008) for both the monitored workers and the measurably exposed workers. For the monitored workers, it is ~0.24 msv against 0.5 msv in conventional and 1.28 msv against 1.6 msv in interventional radiology in And, for the measurably exposed workers, it is ~0.79 against 1.2 msv in conventional and 1.33 against 3.1 msv in interventional radiology in Using the 2005 values from Tables 1 and 2 for comparison is due to the fact that the world figures stand for the mid 2010s (4). The average annual effective doses have descending trends for both measurably exposed and monitored workers over the studied period, i.e. 64 and 26% reduction for conventional and 59 and 55% reduction for interventional radiology. Decreases in these figures are very meaningful and encouraging in both categories. The reasons for it cannot be defined from this study, although the contributing factors probably include employing more advanced devices, better radiation protection training, better working procedures, and stronger regulatory control. Regarding the adherence to a strict monitoring program, no considerable improvement can be seen from 2005 to 2014 in conventional radiology. The returning rate of the used films in this group irregularly varies year by year in the range of 73 81%. The situation is worse in interventional radiology where the returning rate shows a declining trend from 90 to 77% for the same period. All of the centers receive their film badge services from the only service provider that is located in the capital city Tehran. For a big country like Iran, one of the reasons for the mentioned problem can likely be the distance. The ratio of conventional radiology radiation workers whose over a year are all <MDL shows a slight decrease from 94% in 2005 to 91% in 2014, while it fluctuates between 40 and 58% in interventional radiology. The rates of are almost constant over the studied period andareoftenaround3%forconventionaland34% for interventional radiology. The rates of >1mSv and >1 msv average annual effective doses, in contrast, decrease considerably from 0.28 and 1.12% to 0.06 and 0.38% in conventional radiology. In interventional radiology, the rates fall from 8 and 25.3% to 1.46 and 17.2%. The stronger regulatory investigation of doses crossing the IL, by informing licensees and practitioners about their incorrect use 41

6 of the dosimeters, could be one reason for this improvement particularly in conventional radiology. The reliability of recorded doses As is already mentioned the directly exposed films are easily recognizable by interpreters trained eyes. Table 3 depicts the statistical results obtained by analyzing the films and questionnaires for the period of As can be seen the rates of questionnaires that have received a response are only 49/125 = 39% and 15/50 = 30% for conventional and interventional radiology in The rates are increased respectively to 75/141 = 53% and 40/50 = 80% in According to Table 3, the frequency rates of >IL cases decrease from 0.28 and 0.69% in 2008 to 0.15 and 0.43% in 2014 in conventional and interventional radiology. The rates of true to successfully investigated >IL cases decline from 26.5 (13/49) and 40% (6/15) to 12 (9/ 75) and 35% (14/40) over the same period. These desirable trends confirm the effectiveness of the investigation process on awareness and/or carefulness of the radiation workers. The majority of the true cases in conventional radiology (except medically exposed ones) have acknowledged that they have occasionally taken part in interventional radiology practices in different departments or centers using the same personal dosimeters, whereas according to the INRA regulations they have to be assigned a separate personal dosimeter for such secondary duties. Thus, however, those >IL cases have been true as occupational personal doses that must be kept under control, the real rates of true >IL cases resulting solely from working in conventional radiology have been in fact less than the depicted figures. Two main reasons for the false, direct exposure of the film and wrong placement or improper use of the film, together are the causes for 91.7 (33/36) and 95.5% (63/66) of high false (>IL) in conventional radiology in 2008 and On the other hand, the main reason for false in interventional radiology is often wrong placement or improper use of the film (77% contribution in both 2008 and 2014). Dose frequency distribution Dose frequency distributions of both categories are presented in Table 4. It is worth reminding that 0.05 msv has been set as the MDL in film dosimetry and that for less than this figure a value of msv is used in calculating the annual personal or collective doses. The prevalence of annual effective dose values is tabulated by dividing it into seven dose bands: <MDL, MDL 1 msv, 1 5 msv, 5 10 msv, msv, msv and > 50mSv. Contributions of the first five ranges to the total population are also calculated every year. The results of the investigation process (Table 3) are considered in Table 4, i.e. the false >IL are removed from the data. As can be seen, the F. MIANJI ET AL. 42 annual effective doses of 91.13% of radiation workers in conventional radiology were <0.15 msv in 2014 (this means all the six periods were <MDL). In the same year, 8.81% of the radiation workers of this group received annual doses in the range of msv and only 0.06% of them were above 1 msv (in the range of 1 5 msv). Therefore, 99.94% of the radiation workers received annual doses less than the public dose limit. The rate of >1mSv annual dose shows a continuous decreasing trend from ~1% in 2005 to ~0.5% in 2008 (the year that the evaluation of >1mSv was commenced) and then to only 0.06% in The investigation showed that all the >5mSv were false (directly exposed films). Regarding interventional radiology, the rates are much different. Only 49.43% of radiation workers in this group had annual effective doses <0.15 msv while 33.38% of them received doses in the range of msv in Thus, compared to the conventional method, a much higher percentage of radiation workers (17.19%) received doses above 1 msv in 2014 (the rate was 25.32% in 2005). Although the rates of 3.69% (for 5 10 msv) and 2.09% (for msv) in 2005 show dramatic declines respectively to 0.91 and 0.19% in 2014, these occurrence rates cannot be ignored yet. On the other hand, the rate for 1 5 msv is only slightly moderated ( %). The frequency of six msv doses in 2005 is decreased to three and then to one in 2006 and 2008, respectively. Same as the very rare >50 msv cases, they were physicians who declared that the high doses had been due to their very high workloads in angiography. Using personal dosimeters is mandatory for personal dose monitoring in conventional and interventional radiology in Iran (17), and probably in many other countries. The results of this study challenge this regulation for conventional radiology. Appreciating the low dose levels in conventional techniques, substituting the passive personal dosimetry method with workplace monitoring can be an option. Other options are elongating the personal monitoring period to more than 2 months (taking the film characteristics into account), or replacing passive personal monitoring with active techniques. Film badge dosimetry showed no deficiency in the monitoring programs of the centers, thus, moving to other techniques such as TLD or OSL seems disadvantageous at least in terms of reliability of the recorded doses. Comparing the results with other countries The findings of this work are compared with the reports of 14 countries from UNSCEAR (4) and two independent reports from China (7) and Pakistan (8). The most recent UNSCEAR data are for , thus, the figures for 2005, , and periods respectively from Iran, China, and Pakistan

7 Table 3. The annual frequency of >1mSv and the main reasons found by the INRA investigation. 43 Year Type of radiology Total # of interpreted films Con Int Total # of films with doses >IL Con. (>1 msv) Int. (>3 msv) Occurrence rate of recorded doses >IL Con. (>1 msv) 0.28% 0.16% 0.21% 0.13% 0.16% 0.12% 0.15% Int. (>3 msv) 0.69% 0.77% 0.37% 0.50% 0.48% 0.31% 0.43% Total # of > IL with completed investigation Con. (>1 msv) Int. (>3 msv) Total # of true cases >IL Con. (>1 msv) Int. (>3 msv) Occurrence rate of real >IL doses Con. (>1 msv) 0.029% 0.024% 0.025% 0.015% 0.01% 0.013% 0.009% Int. (>3 msv) 0.083% 13% 22% 24% 13% 26% 0.12% # False : due to medical exposure of R.W. Con. (>1 msv) Int. (>3 msv) # False : direct exposure of the film Con. (>1 msv) Int. (>3 msv) # False : wrong placement or improper use of the film Con. (>1 msv) Int. (>3 msv) Defective badge or film Con. (>1 msv) Int. (>3 msv) A COMPARISON OF OCCUPATIONAL DOSES IL, investigation level; Con., conventional radiology; Int., interventional radiology.

8 Table 4. Dose frequency distribution in conventional and interventional radiology. Year Type of radiology # R.W. All < MDL ( 0.15 msv) msv 1 5 msv 5 10 msv msv msv >50 msv # R.W. % R.W. # R.W. % R.W. # R.W. % R.W. # R.W. % R.W. # R.W. % R.W Con Int Con Int Con Int Con Int Con Int Con Int Con Int Con Int Con Int Con Int F. MIANJI ET AL. Con., conventional radiology; Int., interventional radiology.

9 Table 5. Comparison of the situation in Iran with some other countries. Country Type of radiology Period MDL (msv) Dose recorded when <MDL (msv) Monitored workers (10 3 ) Measurably exposed workers (10 3 ) Average annual effective dose (msv) Monitored workers Measurably exposed workers % R.W. with annual ED < 1 msv 45 Iran Con Int United Kingdom Con Int Kuwait Con Int Croatia Con Int Belarus Con Int Czech Rep. Con Int Romania Con Int Netherlands Con Int Denmark Con Int Finland Con a Int Philippines Con Int Slovakia Con Int Luxembou-rg Con Int Cyprus Con Int Hungry Con Int China Con. + Int b Pakistan Con. + Int A COMPARISON OF OCCUPATIONAL DOSES Con., conventional radiology; Int., interventional radiology; ED, effective dose. a In 3 months. b Annual ED < 5 msv.

10 are chosen and included in Table 5. Reports of China and Pakistan do not define separate information for conventional and interventional radiology; therefore, their data cannot be used for comparisons with other countries (unless each country s data is combined first). The data from the UK and China do not include the rate of annual ED < 1 msv. As is shown in Table 5, in 11 of 15 countries that have defined this rate, at least 90% of conventional radiology radiation workers received annual effective doses below 1 msv. Iran and Denmark with 99% have the highest rate of annual ED < 1 msv. The lowest rates belong to Belarus (16%), Slovakia (22%) and Cyprus (68%). Regarding interventional radiology, frequency of <1 msv annual doses varies greatly from 6 and 10% for Romania and Slovakia to 97 and 99% for Denmark and Hungary. Iran with 74.68% is eighth. The average annual effective doses are also very different according to the table. For measurably exposed workers in conventional radiology, the UK with only 0.07 msv is the lowest and Slovakia with 1.79 msv is the highest while Iran stands in between with 0.79 msv. The variety of average annual effective doses in interventional radiology is much higher where again the UK is on the lower end (0.21 msv) and Slovakia with 3.79 msv is on the other end of the range. Iran (1.28 msv) is among the 10 countries with average annual effective doses (measurably exposed workers) below 2 msv. As can be seen, MDLs and recording values assigned for <MDL doses vary from country to country. While the average annual effective doses in countries like Kuwait, Belarus and Cyprus are the same for monitored and measurably exposed workers, in the Philippines (conventional) and Hungary (interventional) they differ by a factor of 11. CONCLUSION Thorough investigations of personal occupational doses of radiation workers in conventional as well as interventional radiology were carried out. The findings of this research ensure the negligibility of occupational doses in conventional radiology in Iran and propose reconsideration of the obligation of (or the monitoring period of) wearing personal dosimeters in this category in Iran. In interventional radiology on the other hand, relatively higher annual doses in the range of 1 5 msv (16% in 2014) confirms the need for improvements in safety. Despite the considerable decrease in the frequency rate of >5 msv annual doses in interventional radiology, from 5.8% in 2005 to 1.1% in 2014, greater effort should be expended to further optimize the rate. The results also confirm that the dosimetric data of any particular country cannot be used for any other countries due to the considerable differences that possibly exist among them. Non-identical MDLs and different F. MIANJI ET AL. 46 policies for recording dose values less than the MDL, used personal dosimetry techniques, evaluating method of anomalous, managing missing periods in the, differences in determining who is a radiation worker, etc. are some of the causes that may play very important roles besides the technological issues and safety culture, in this regard. Improper use of personal dosimeters was recognized as the main reason for the false high doses (crossing the ILs) in both of the groups. On the other hand, non-wearing personal dosimeters seems an important issue that may contribute to the high rate of non-measurably exposed personal dosimeters particularly in interventional radiology. It is shown than the regulatory follow-up of such cases is an effective method in decreasing both the false and real high doses, probably by improving the safety awareness of radiation workers. Therefore, strengthening of such controls is recommended. ACKNOWLEDGMENT The authors would like to thank Ms Shadi Nemati for her technical supports on the NODR system. FUNDING This research work was supported by Iran Nuclear Regulatory Authority (INRA) and Nuclear Science and Technology Research Institute (NSTRI). REFERENCES 1. IAEA. Applying Radiation Safety Standards in Diagnostic Radiology and Interventional Procedures Using X Rays, Safety Reports Series (Vienna: International Atomic Energy Agency) (2006) ISSN ; No Antic, V., Ciraj-Bjelac, O., Rehani, M., Aleksandric, S., Arandjic, D. and Ostojic, M. Eye lens dosimetry in interventional cardiology: results of staff dose measurements and link to patient dose levels. Radiat. Prot. Dosim. 154(3), (2013). 3. Vano, E., Gonzalez, L., Beneytez, F. and Moreno, F. Lens Injuries Induced by Occupational Exposure in Non-Optimized Interventional Radiology Laboratories. Br. J. Radiol. 71(847), (1998). 4. Sources and Effects of Ionization Radiations. UNSCEAR 2008, Volume 1, Annex B, New York, Sources and Effects of Ionization Radiations. UNSCEAR 2000, Volume 1, Annex E logists-it-depends-on-who-you-ask/ 7. Wu, W., Zhang, W., Cheng, R. and Zhang, L. Occupational exposure of Chinese medical radiation workers in Radiat. Prot. Dosim. 117, (2005).

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