Estimating the population dose from nuclear medicine examinations towards establishing diagnostic reference levels.

PURPOSE OF THE STUDY: This study conducted a review on nuclear medicine (NM) services in Mazandaran Province with a view to establish adult diagnostic reference levels (DRLs) and provide updated data on population radiation exposure resulting from diagnostic NM procedures.
MATERIALS AND METHODS: The data were collected from all centers in all cities of Mazandaran Province in the North of Iran from March 2014 to February 2015. The 75(th) percentile of the distribution and the average administered activity (AAA) were calculated and the average effective dose per examination, collective effective dose to the population and annual effective dose per capita were estimated using dose conversion factors. The gathered data were analyzed via SPSS (version 18) software using descriptive statistics.
RESULTS: Based on the data of this study, the collective effective dose was 95.628 manSv, leading to a mean effective dose of 0.03 mSv per capita. It was also observed that the myocardial perfusion was the most common procedure (50%). The 75(th) percentile of the distribution of administered activity (AA) represents the DRL. The AAA and the 75(th) percentile of the distribution of AA are slightly higher than DRL of most European countries.
CONCLUSIONS: Myocardial perfusion is responsible for most of the collective effective dose and it is better to establish national DRLs for myocardial perfusion and review some DRL values through the participation of NM specialists in the future.

INTRODUCTION

In recent years, the use of ionizing radiation in medical imaging has increased and led to the remarkable increase of collective effective dose to the population.[1] The ionizing radiation dose due to medical imaging in the North of Iran was estimated in 2006 while It was estimated 9.6 μSv per capita.[2]

Nuclear medicine (NM) diagnostic imaging has a significant contribution in the ionizing radiation population exposure.[3] There is a raise in the annual frequency of NM diagnostic procedures per 1000 individuals from 11 individuals in 1970s to 19 people in 2008 according to the report of the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and report no. 154 of the European Commission.[4] Collective effective dose comprises of NM procedures within the range of 0.4–14.5%.[1] Hence, justification and optimization of examination in NM departments are highly recommended in near future to avoid unnecessary collective effective dose.

The concept of diagnostic reference level (DRL) was pointed out by the International Commission on Radiological Protection (ICRP) publication 60,[5] and in later publications (73.103.105)[678] summarized previous definitions and recommendations on DRLs and their different fields of application.

The Medical Exposure Directive (97/43/Euratom)[9] defines DRLs as “Dose levels in medical radiodiagnostic practices or, in the case of radiopharmaceuticals, levels of activity, for typical examinations for groups of standard-sized patients or standard phantoms for broadly defined types of equipment. These levels are not expected to exceed for standard procedures when the good and normal practice regarding diagnostic and technical performance is applied.” The DRLs can be obtained from the activity distribution as the third quartile.[71011] In NM reference administered activity (AA), is an activity requiring for a good image during standard methods.[12]

We conducted a review of NM services in Mazandaran, with outlook to establish adult DRLs and estimate radiation exposure to the population for common NM examinations.

MATERIALS AND METHODS

All hospitals and private clinics (7 NM departments) in all cities of Mazandaran in the North of Iran participated in this study from March 2014 to February 2015.

The survey was started through distributing and filling out the checklist on equipment and the procedures including the name of center, scanner manufacturer, year of installation, height and weight of patients, type and amount of AA per procedure as shown in Table 1.

Table 1

Details of Gamma camera scanners and number of patients

Eight common diagnostic scans constituting more than 90% of all NM examinations currently performed in Mazandaran were chosen to propose DRLs.

Each scan involved all adult standard-size patients (typically 70 ± 15 kg) selected from each center and the net injected activity was recorded for 6 scans per type from 7 centers by measuring the remaining activities in the syringes. The net activity was obtained using the following formula: (Total activity − remained activity). All cameras were passed quality control tests according to National Electrical Manufacturers Association guidelines, and all dose calibrators were calibrated by The Secondary Standard Dosimetry Laboratory of Iran. Information on population was obtained from the statistical center of Iran.[13] The gathered data were analyzed via SPSS version 18.0 (2009 SPSS, Inc., an IBM Company, Chicago, Illinois, USA) using descriptive statistics. Moreover, the 75th percentile of the distribution and average administered activities (AAAs) for each procedure were calculated.

The dose per capita from diagnostic NM examinations was estimated using the following formula:

A, CF, NE, and NP are shown the net activity, conversion factor calculated using (ICRP) 106 and 80,[1415] the number of examination and the number of inhabitants who make up the population, respectively.

RESULTS

The range, AAAs and effective dose per procedures are presented in Table 2. The Basic Safety Standards (BSS), Administration of Radioactive Substances Advisory Committee (ARSAC), UNSCEAR 2008 and DRL values for some countries - exactly written from RP 180 part 2/2 report-[1116] were compared to the 75th percentile of the distribution as shown in Table 3.

Table 2

AAAs and effective dose per procedures for common NM examinations

Table 3

The 75% of administered activity in Mazandaran in comparison with BSS, UNCEAR 2008, ARSAC, and some European countries

The annual percentage frequency distribution of common procedures is shown in Figure 1. Figure 2 indicates the 75th percentile and the AAAs of myocardial scan obtained from this study were compared with some DRL data from other countries published in the RP 180 report.

Figure 1

The annual percentage frequency distribution of common procedures

Figure 2

Comparison of diagnostic reference levels for myocardial perfusion, Tc-99m methoxyisobutil isonitrile

It is necessary to say that the mean height and weight of the patients was 161 and 70, respectively.

The population was 3,155,000 and the number of NM procedures in 1 year in Mazandaran was 21290. The number of NM procedures on children was 1903 (9%). The frequency of NM procedures per 1000 population was 6.7 and the mean effective dose per procedure was calculated 4.67 mSv. The collective effective dose from diagnostic NM procedures has been estimated to be 95.628 manSv, with an annual average effective dose of 0.03 mSv per capita. Myocardial perfusion scan accounted for 67% of total collective effective dose followed by bone and thyroid with about 19% and 8%, respectively.

DISCUSSION

The AAAs were higher than ARSAC recommended values, in agreement with UNSCEAR 2008 in TL, bone and DTPA scans. In thyroid scan, AAA was lower than UNSCEAR 2008 and higher than it in the lung and DMSA scans. AAAs were slightly higher than BSS and Iran protocol recommended values except lung scan. While in other cases the mean AA was very close to UNCEAR 2008.

The 75th percentile of the distribution of AA was higher than ARSAC, BSS, and Iran protocol values, and also the 75th percentile was slightly higher than UNSCEAR 2008 except for thyroid, bone, and TL scans, that the first one was being lower it, and the latter two items were in agreement with it.

The 75th percentile of the distribution and the AAAs of myocardium scan in a 2-day protocol were higher than UNSCEAR 2000 although UNSCEAR 2008, BSS and ARSAC have not considered any value for it. The current study represented that the mean AA and the 75th percentile of the distribution of AA were slightly higher than DRL of most countries; however, in some cases, fewer countries such as Luxembourg and Spain were lower than those values.[16]

The estimated effective dose was inconclusive due to nonuniform distribution of activity within particular organs and using biokinetic data. Nevertheless, the effective dose is useful to estimate the risk of stochastic effects.[15]

The result obtained, for the year 2014 represents a marked shift in the type and frequency (distribution) of procedures. The highest number of procedures was myocardial perfusion and bone scan. This result is not the same as the previous reports. The measured data were higher than that in the study of Shabestani et al. in Northern Iran[17] but it was similar to the result of Teles et al. in Portugal in 2010 and Mettler et al. in the USA in 2008[1819] and this may be owing to an increase in the prevalence of myocardial related-disease in this region during the last decade.

In comparison with previous research in 2004, the annual total number of diagnostic NM procedures has enhanced 3 times while the population has increased approximately 9%. The mean effective dose increased from 4.25 mSv to 4.67 mSv. Again, a rise for the annual average effective dose per capita, from 9.3 μSv to 0.03 mSv, was observed.[17] and this per capita dose was greater than the total per capita dose from both diagnostic radiology and NM examinations in 2004, similar to the results reported by Mettler et al. in the USA in 2007.[219] These increases were almost entirely due to the growth of NM diagnostic procedures, which need higher activity to perform.

The total number of NM procedures per 1000 members of population was 6.7 and is lower compared to European countries ranging from 8 to 56.[20]

The annual average effective dose per capita in this study such as Sweden (0.03 mSv), Norway (0.03 mSv), and Finland (0.03 mSv) was lower than that in Australia (0.07 mSv), Switzerland (0.05 mSv), France (0.09 mSv), Italy (0.08 mSv), and Luxembourg (0.15) because of the lower number of NM procedures in Iran.[121]

CONCLUSION

The present study indicated that the high value of patient dose in NM. The myocardial perfusion scan contributes the main part of this dose regarding its high frequency compared to the other types of scans. Therefore, we think that myocardial perfusion scan is a good type of scan for providing DRL in NM.

Financial support and sponsorship

Deputy of research and technology of Babol University of Medical Sciences.

Conflicts of interest

There are no conflicts of interest.