Radiation Protection Dosimetry Advance Access published November 3, Radiation Protection Dosimetry (2010), pp. 1 5

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1 Radiation Protection Dosimetry Advance Access published November 3, 2010 Radiation Protection Dosimetry (2010), pp. 1 5 doi: /rpd/ncq330 NUCLEAR MEDICINE ANNUAL EXTERNAL OCCUPATIONAL DOSE DISTRIBUTION: RIO DE JANEIRO, BRAZIL, YEAR 2005 Claudia L. P. Mauricio 1, *, Ana L. S. Lima 1, Herica L. R. da Silva 1, Denison Souza-Santos 1 and Claudio R. Silva 2 1 Instituto de Radioproteção e Dosimetria, IRD/CNEN, Av. Salvador Allende s/n, Rio de Janeiro, Brazil 2 Coordenação-Geral de Ciência e Tecnologia da Informação, CGTI/CNEN, Rua General Severiano, 90, Rio de Janeiro, Brazil *Corresponding author: claudia@ird.gov.br Brazil has about 300 nuclear medicine services (NMS), 44 of them located in the state of Rio de Janeiro (RJ). Most nuclear medicine staff are routinely monitored for external dose. This paper makes a statistical analysis of all the RJ NMS annual external occupational doses in year Around 100 professionals of RJ NMS received annual doses >4.0 msv, considering only external doses, but no one receives doses higher than the mean annual dose limit of 20 msv. Extremities dosemeters are used by about 10 % of the staff. In some cases, these doses are more than 10 times higher than the dose in thorax. The maximum ratio of extremity dose/thorax dose, in 2005, was 72. This study shows the importance to improve radiation protection procedures in nuclear medicine, mainly because the number of occupational individuals in nuclear medicine and their external doses are increasing. INTRODUCTION Nuclear medicine is a medical area that employs radioactive materials for tomographic procedures in diagnosis, treatment and prevention of diseases. It allows the acquisition of anatomy and function organs data. The most commonly used techniques are the single photon emission computed tomography (SPECT) and the positron emission tomography (PET) (1). SPECT imaging is performed, by using a gamma camera, to acquire multiple Two-dimensional images ( projections) from multiple angles. A computer program is used to apply a tomographic reconstruction algorithm to the multiple projections, yielding a three-dimensional (3-D) data set. In a PET examination, a positron that is emitted from the nucleus of an atom annihilates in the surrounding medium, emitting two back-to-back photons in the centre of mass reference frame. Those photons are detected by coincidence counting in a gamma camera, revealing the presence of the original positron. PET studies reveal the in vivo distribution and kinetics of positron emission radiopharmaceuticals (2). Today, PET is the most advanced expensive and sophisticated service in the field of nuclear medicine. To perform both examinations, a special drug marked with radioactive material must be given to the patient. A gamma camera is then placed in convenient positions to perform the photon counting, which is used to reconstruct a full 3-D distribution of the radionuclide inside the body or organ. SPECT and PET examinations in nuclear medicine allow the earlier detection of functional or structural abnormalities of an organ, making it possible to treat some diseases. Diagnosing earlier, there is a higher chance of a successful forecast and quick patient s recovery. Nuclear medicine procedures are, by the standards of technology-intensive medicine, relatively low-cost, safe and minimally invasive (3). Therefore, the number of procedures carried out has been increasing in the last decades. However, the staff are potentially exposed to ionising radiation, mainly nuclear medicine pharmacists, technicians and nurses while carrying out a variety of tasks associated with the nuclear medicine procedures. This is due to the fact that some of them have to stay close to the radionuclides during the preparation of radiopharmaceuticals and to the patients who became sources, after incorporation. For example, they can be exposed while the radiopharmaceutical is being prepared or administered to the patient, while positioning the gamma camera and while assisting the patient. The high and increasing number of patients who undertake examinations in nuclear medicine and of workers involved in this practice justifies efforts towards improving the quality of diagnosis and reducing the radiological risks associated with this practice. The dose of the patient in this procedure is low compared with the dose in a procedure that uses computed tomography, but the external occupational dose is higher. This work makes a statistical analysis of all 2005 annual external occupational doses and monthly doses.4.0 msv from 2004 to 2009, received by nuclear medicine staff from the Brazilian state of Rio de Janeiro (RJ). # The Author Published by Oxford University Press. All rights reserved. For Permissions, please journals.permissions@oxfordjournals.org

2 C. L. P. MAURICIO ET AL. Table 1. Brazilian authorised photon external individual BRAZILIAN NMS monitoring services, SMIE. According to the CNEN, there are about 300 NMS SMIE State Detector in Brazil, 44 of them in the state of RJ. In terms of the number of users of external individual monitoring, the state of RJ has about 13 % of all monitored CDTN/CNEN Minas Film Gerais workers in Brazil. Mainly after the introduction of CIDRA São Paulo TLD PET technology in Brazil, the number of people ELETRONUCLEAR RJ TLD working in these services is increasing very quickly. IFUSP São Paulo TLD In 2003, Brazil had about 4000 externally monitored IPDR São Paulo TLD workers in the area of nuclear medicine. In 2005, IPEN/CNEN São Paulo TLD they were already about 6000, and in 2008, this IRD/CNEN RJ Film number exceeded In RJ, besides SPECT procedures, PET examinations started to be offered in DEN/UFPE Pernambuco Film PRO-RAD Rio Grande TLD 2005, with the production of the F-18 in RJ city. do Sul SAPRA/ São Paulo TLD The number of RJ NMS externally monitored LANDAUER workers jumped from about 400 in 2003 to about TEC-RAD São Paulo TLD 800 in 2005 and more than 1000 in However, the complete dose assessment of workers in nuclear medicine requires the application of techniques for external and internal (measured in vivo and in vitro ) individual monitoring to quantify the incorporation and to evaluate the effective dose. Nevertheless, in Brazil, only external individual monitoring is required for all nuclear medicine staff. This monitoring has to be routinely done in a monthly basis by one of the Brazilian SMIEs presented in Table 1. Internal individual monitoring is not routinely done, being demanded only in case of suspicion of an incident or accident. BRAZILIAN NUCLEAR AND RADIOLOGICAL REGULATION Comissão Nacional de Energia Nuclear (CNEN) is the Brazilian governmental agency responsible for the licence and control of all nuclear and radiological installations in their practices involving ionising radiation, except in medical and odontological radiology installations, which are Health Ministry s responsibility. CNEN defines legal security requirements that have to be accomplished for nuclear and radiological installations. All Brazilian nuclear medicine services (NMS) have to follow CNEN regulations. According to the Brazilian law, external individual monitoring for photons using thorax dosemeter is compulsory for all individuals working in controlled areas, as those of NMS. This individual monitoring has to be provided only by authorized individual monitoring service Serviço de Monitoração Individual Externa (SMIE). All SMIEs in Brazil have to receive an authorisation before starting measuring the external dose of workers. A CNEN institute, the Instituto de Radioproteção e Dosimetria (IRD) is responsible for the surveillance of the fulfilment of rules stretched out in the regulation, granting authorisation to the SMIEs. For thorax dosemeter, up to now, in Brazil, the standardized quantity to be measured by all authorized SMIEs is the photon dose equivalent. Table 1 presents the name, location and type of detector used for the actual 11 authorized Brazilian SMIE. One of the SMIEs requirements to maintain their permission is to send all the measured doses annually to the Brazilian National External Occupational Dose Database at IRD. They also have to send to IRD all monthly thorax doses.4.0 msv and monthly extremity doses.40.0 msv. METHODOLOGY The data analysed in this study are all from IRD/ CNEN Brazilian National Database of external occupational doses. Only monitored workers of NMS in the state of RJ (RJ NMS) have been included in the analysis. A problem with the loaded annual doses of one of the authorized SMIEs after 2005 was identified and, therefore, all of its annual doses from 2006 onwards were deleted from the database and are being reloaded step by step. Then, only 2005 thorax and extremity annual doses were used for this paper. No problems were found on the monthly high thorax and extremity doses, and they were also studied for better comprehension of their evolution from 2004 to The annual doses were analysed according to workers function and dosemeter type. In this work the records from thorax dosemeters, measuring photon dose equivalent, are considered as real occupational effective dose. The ones from ring and bracelet dosemeters, measuring photon personal dose equivalent at 0.07 mm depth, are interpreted as real extremity equivalent dose. Both assumptions neglect the misuse of the individual monitors and field inhomogeneities. Page 2 of 5

3 NUCLEAR MEDICINE DOSE DISTRIBUTION: RIO DE JANEIRO, 2005 Figure 1. Histogram of RJ NMS annual external effective dose distribution in 2005, by staff function. RESULTS The Brazilian National External Occupational Dose Database, in 2005, has 791 thorax doses and 80 extremity doses registered for RJ NMS, about 50 % for thorax and 20 % for extremity with dose value lower than monthly dose record level of 0.2 msv (4). The number of monitored people is lower than the number of annual doses, because some of the professionals work in more than one NMS, mainly doctors and medical physicists. In RJ, one of the nuclear medicine doctors works in five NMS and one medical physicist, in six. Technicians and nurses normally work in only one NMS, at most in two. The number of people monitored in RJ NMS for occupational exposure in 2005 is 721: 173 technicians, 157 doctors, 133 nurses, 33 biologists, 12 pharmacists, 11 medical physicist and the others with other functions. Considering the thorax measurement as effective dose and comparing with Brazilian annual limits (5), about 50 % of the annual doses were higher than the limit for public (1.0 msv) and about 10 % were higher than the annual investigation level for occupationally exposed individuals of 6.0 msv (4), but no one was higher than the mean occupational annual limit of 20.0 msv (5). The highest annual effective dose was 18.2 msv, received by a nuclear doctor. However, doctors doses are normally lower, even considering that they work in several NMS, since they typically have little contact with patients and/ or radiopharmaceuticals during nuclear medicine Table 2. Monthly effective dose >4.0 msv received by RJ NM staff. Year Number of monthly doses Number of workers Highest monthly dose (msv) Highest annual dose (msv) procedures. Classifying the doses divided in classes of 1 msv and separating their values for professionals function, it can be seen that the largest number of high doses is received by technicians and nurses, but the highest percentage occurs for pharmacists. Figure 1 shows, in a histogram form, this dose distribution. Table 2 shows a summary of the number of the monthly occupational thorax doses.4.0 msv from 2004 to 2009, the number of workers exposed to them and their highest monthly and annual estimated effective dose. Technicians, nurses and pharmacists received all of these higher doses. Although the number of people working in nuclear medicine is rising, the number of overexposure seems to be Page 3 of 5

4 C. L. P. MAURICIO ET AL. Figure 2. Histogram of RJ NMS annual extremity dose distribution in 2005, by staff function. Figure 3. Histogram of RJ NMS annual extremity to effective dose ratio in decreasing, despite some high dose values measured in 2006 and These values are even greater than the annual limit. Considering the 721 RJ NMS occupationally monitored staff in 2005, only about 10 % wore extremity monitors: 43 technicians and nurses, 13 doctors, 4 pharmacists, and 16 with other functions. These 76 people have 80 extremity registers on the Brazilian National Occupational Dose Database, of which only 2 were measured with bracelet dosemeters and all others with ring dosemeters. Classifying the doses divided in classes of 10 msv and separating their values for professionals function, it can be seen that the largest number of high doses is received by pharmacists, technicians and nurses, Figure 2 shows, in a histogram form, this dose distribution. The extremities annual doses of the RJ NMS staff in 2005 varied from 0 to 71 msv that is,150 msv, which is the Brazilian annual investigation limit for Page 4 of 5

5 NUCLEAR MEDICINE DOSE DISTRIBUTION: RIO DE JANEIRO, 2005 extremity dose (5). However, in many cases, the extremity dose is more than 10 times higher than the dose measured on the thorax, which reinforces the necessity of this additional individual monitoring. About 50 % of thorax doses lower than the register level of 0.2 msv (4) present some registered value on the extremities individual monitors, varying from 0.2 to 5.4 msv. Figure 3 shows, in a histogram form, the ratio of extremity to thorax doses, considering thorax dose to be 0.1 msv, where it is lower than the recording level of 0.2 msv. Technicians and nurses received, in 70 % of cases, doses in their extremities higher than in their thorax (ratio.1), being the ratio.10 for about 10 % of measurements. For pharmacists, 50 % of this ratio value is.1 and 20 %is.10. For doctors, 40 % of this ratio is.1 and 8% is.10. Considering only the monthly extremities doses.40 msv, from 2004 to 2009, only four values for pharmacists has been recorded. These values were measured one in 2004 (52.7 msv), two in 2007 (41.3 and 48.3 msv) and one in 2009 (69.5 msv). CONCLUSIONS As expected, pharmacists, technicians and nurses receive the highest external doses. This is due to the fact that, considering the NMS staff, they are the ones who stay closer to the radionuclides during the preparation of radiopharmaceuticals and to the patients who become sources, after incorporation. In RJ, 47 % of annual measured thorax doses, for calendar year 2005, are below the record level and 52 %,1 msv. The highest annual dose measured is smaller than occupational annual individual dose limit, but 10 % are higher than the Brazilian investigation level. This can happen due to lack of investigation or adoption of corrective action not effective. Thus, constant effort must be taken to improve the radiation protection in NMS, in order to optimise these doses, mainly because the number and complexity of nuclear medicine procedures are quickly increasing along the years. Annual doses of 58.2 and 64.6 msv are received, respectively, in 2006 and 2008, for two different technicians of RJ NMS, values that are much higher than the annual occupational dose limit. In RJ NMS, normally, the radiopharmaceuticals are prepared by technicians and not only by pharmacists. This explains their higher extremity doses. When they use the dosemeter correctly, doses of extremities are higher than doses of thorax, because their hands are closer to radiopharmaceuticals during manipulation. Nevertheless, few workers receive extremity dosemeters and, even when they do, they are not inclined to use it. Further work will be executed to verify in practice the frequency of the use of dosemeters and reasonable doses according to practices. REFERENCES 1. Leslie, W. D. and Greenberg, I. D. Nuclear Medicine. Landes Bioscience (2003). 2. Wernick, M. N. and Aarsvold, J. N. Emission Tomography: The Fundamentals of PET and SPECT. Academic Press (2004). 3. Stabin, M. Nuclear medicine dosimetry. Phys. Med. Biol. 51, (2006). 4. CNEN Comissão Nacional de Energia Nuclear. Restrição de dose, Níveis de Referência Ocupacionais e Classificação de Áreas. CNEN PR 3.01/004, Brazilian National Press (2005). 5. CNEN Comissão Nacional de Energia Nuclear. Diretrizes Básicas de Proteção Radiológica. CNEN NN- 3.01, Brazilian National Press (2006). Page 5 of 5