Radiation Protection Dosimetry Advance Access published January 23, 2014 Radiation Protection Dosimetry (2014), pp. 1–9
doi:10.1093/rpd/ncu001
RADIATION EXPOSURE TO NUCLEAR MEDICINE STAFF INVOLVED IN PET/CT PRACTICE IN SERBIA V. Antic1, O. Ciraj-Bjelac2,*, J. Stankovic2, D. Arandjic2, N. Todorovic3 and S. Lucic4 1 Center for Nuclear Medicine, University Clinical Centre of Serbia, Belgrade, Serbia 2 Radiation Protection Laboratory, Vinca Institute of Nuclear Science, University of Belgrade, PO Box 522, Belgrade 11001, Serbia 3 Faculty of Science, Department of Physics, University of Novi Sad, Novi Sad, Serbia 4 Oncology Institute of Vojvodina, Sremska Kamenica, Novi Sad, Serbia
Received 25 March 2013; revised 23 December 2013; accepted 1 January 2014 The purpose of this work is to evaluate the radiation exposure to nuclear medicine (NM) staff in the two positron emission tomography-computed tomography centres in Serbia and to investigate the possibilities for dose reduction. Dose levels in terms of Hp(10) for whole body and Hp(0.07) for hands of NM staff were assessed using thermoluminescence and electronic personal dosemeters. The assessed doses per procedure in terms of Hp(10) were 4.2–7 and 5– 6 mSv, in two centres, respectively, whereas the extremity doses in terms of Hp(0.07) in one of the centres was 34–126 mSv procedure21. The whole-body doses per unit activity were 17– 19 and 21– 26 mSv GBq21 in two centres, respectively, and the normalised finger dose in one centre was 170– 680 mSv GBq21. The maximal estimated annual whole-body doses in two centres were 3.4 and 2.0 mSv, while the corresponding extremity dose in the later one was 45 mSv. Improvements as introduction of automatic dispensing system and injection and optimisation of working practice resulted in dose reduction ranging from 12 up to 67 %.
INTRODUCTION Positron emission tomography (PET) is a modern and non-invasive imaging modality that provides visual and semi-quantitative assessment of functioning of organs and tissues. Computed tomography (CT) is a non-invasive technology that gives the superior morphological image of the observed body region. Using a multimodal PET/CT, the anatomical and metabolic information is displayed in a combined image(1 – 3). The PET procedure involves the administration of the radiopharmaceuticals in the body. The most widely used radiopharmaceutical for clinical PET/CT applications is 18F-fluorodeoxyglucose (FDG)(1, 2). The radionuclide 18F used to label FDG is positron emitter (630 keV), producing high-energy annihilation photons of 511 keV, which causes a relatively high radiation exposure to nuclear medicine (NM) staff. The observed radiation dose is related to the amount of activity in the source and length of time of an individual exposure(4). PET/CT scanners have been commonly installed in the existing NM departments; however, the relatively long uptake phase, high-energy gamma radiation and manipulation of unsealed radiation sources (during dispensing and injection), has put a challenge to keep occupational whole-body and extremity doses as low as reasonable achievable. Many investigations regarding radiation protection of medical staff working in PET/CT departments were conducted worldwide(5 – 19). Some of the studies
indicated high radiation doses due to both radionuclide handling and the interaction with a patient after radionuclide administration(7, 8, 18). Indeed, the higher energy of radiation means that medical staff could receive a higher whole-body dose than those working only with conventional NM radionuclides. Manipulation of unsealed sources in NM, in particular those emitting beta radiation, involves high skin doses to the upper extremities during preparation and injection of the radiopharmaceuticals. Many studies indicated that local skin doses can surpass the annual dose limit of 500 mSv averaged over 1 cm2(20 – 22). Therefore, international investigations were directed to dosimetry for extremities in PET/CT practice(15, 17). Dose to the staff can be minimised in multiple ways, mainly by training them in applying basic radiation principles such as maintaining distance from the radiation source or patient (19, 23), performing operations in a shortest possible time(24) and using shielding (shielded dispensers, etc.) whenever practicable(18, 25). The occupational exposure in PET imaging can also be controlled by rotating the staff members in performing particular duties, avoiding the close contact with the radioactive source, using semi-automatic or automatic injector, video and audio monitoring and communicating with injected patients(6). The aim of the present work is to provide an overview and analyse the magnitude of radiation exposure in terms of whole-body and extremity doses to NM
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*Corresponding author: [email protected]
V. ANTIC ET AL.
staff working in PET/CT practice in Serbia, and accordingly, to discuss introduced methods for dose reduction as automated dispensing and injection system, and optimisation of routine working practice. MATERIALS AND METHODS
Dosimetry International Basic Safety Standards(26) recommends the use of personal dose equivalents Hp(0.07) for doses to the extremities, Hp(3) for doses to the lens of the eye and Hp(10) for doses to the whole body, as relevant operational quantities for individual monitoring of external radiation. Typically, a single whole-body dosemeter is used for individual monitoring of external radiation. However, several studies confirm that NM personnel should be equipped not only with wholebody dosemeters, but also with thermoluminescence dosemeter (TLD) for extremity monitoring(20, 22, 27). Staff in both PET/CT centres in Serbia is routinely monitored using TLDs and personal electronic dosemeters (EDs) worn at the chest level. TLD for extremity monitoring, DXT-100 ringlet, was inserted into a plastic ring holder, which was worn on the index finger base of the dominant hand of staff in one centre. The routine monitoring service is provided by accredited laboratories of Institute of occupational health: Belgrade, Serbia (for centre A) and Vinca Institute of Nuclear Sciences, Belgrade, Serbia (centre B), both using Harshaw 6600 readers. Calibration of dosemeters in terms of Hp(10) and Hp(0.07) was performed at Secondary Standard Dosimetry Laboratory of Vinca Institute of Nuclear Sciences, Belgrade, which is accredited to EN ISO/IEC 17025. The basic information on PET/CT units and dosemeters used in these institutions is summarised in Table 1.
A PET/CT procedure in both centres consists of multiple steps. The first step is the receipt of the radiopharmaceutical in the transport container. The FDG is further handled in the ‘hot’ laboratory, which includes measuring the delivered activity, calculating activity/time and dispensing of the multidose activity in the syringes for single injection, and subsequently the injection of radiopharmaceuticals to the patients. The last step includes the time spent in collection and escorting the patients to the imaging room, positioning and, after image acquisition, escorting of patients out of the NM department. All these steps contribute to the dose to NM staff, depending on the facility design and level of radiation protection applied. In centre A, two different teams are taking care of patients. Approximately 10 patients are examined per day and each team is working 1 d week21 on the PET/CT modality. Each team consists of two physicians, a technologist and a radiochemist. In 2011, before the introduction of an s for dispensing and injection into the practice, the radiochemist was responsible for manual radiopharmaceutical dispensing and the technologist for injection and patient escorting and positioning. In this period, physicians were present during the injection phase supervising the whole procedure. When the automated system for dispensing and injection was introduced in October 2011 (MEDRAD, IntegoTM PET Infusion System), physicians have become equally involved in the activities related to the dispensing and injection of radiopharmaceuticals as other two team members. Still, the technologist remains to be the person most frequently nearest to the patient. It is important to note that in both periods during injection of the radiopharmaceuticals the whole team was present in the room, sharing the responsibility for patient management from the beginning to the end. Practice in centre B is different. There are six technologists exclusively working at PET/CT facility. In this centre, staff is rotationally changing in performing different duties. One technologist takes care of one patient at the time, performing all above-mentioned
Table 1. The basic information about PET/CT centres in Serbia. Name of institution
Institute for Oncology Sremska Kamenica Centre A
PET/CT unit (manufacturer/model) Radiopharmaceutical Personal dosemeters (whole body) Personal dosemeters (extremities) Personal EDs (whole body)
Siemens Biograph True Point 40/64 F-FDG (multidose vial) Harshaw TLD-100H Not available Mirion DMC 2000XB
18
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National PET Centre in Clinical Centre of Serbia Centre B Siemens Biograph True Point 40/64 18 F-FDG (multidose vial) Harshaw TLD-100 Harshaw DXT-100 Mirion DMC2000X, DMC2000XG
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PET/CT practice in Serbia is currently conducted in two medical centres. Both sites are using the same model of PET/CT unit and 18F-FDG as the only radiopharmaceutical. According to data retrieved from administration from both centres, 2000 procedures are performed annually in Serbia.
Workpractice
OCCUPATIONAL RADIATION DOSE IN PET/CT
Data collection Data about the occupational dose to NM staff involved in PET/CT practice were collected from both institutions in Serbia in the period 2011– 12. In this work, the doses were analysed for two different periods: (1) Period I: Without the automated system for dispensing and injection in centre A and before the training in centre B (data were available from March to September 2011); (2) Period II: With the automated system for dispensing and injection in centre A and after the training in centre B (data were available from March to September 2012). Data were obtained for 10 staff members involved in PET/CT practice: two physicians, one technologist
and one radiochemist from centre A and six technologists from centre B. Data collection was performed in both centres for periods I and II in terms of the number of procedures per month, administered activity per each procedure, Hp(10) per day using ED, Hp(0.07) per month measured using TLD (only in centre B) and Hp(10) per month measured using TLD. The measured dose values, both in terms of Hp(10) and Hp(0.07) were normalised to the total manipulated activity. In addition, the total maximal and typical annual dose were estimated based on the information about cumulative doses during 7 months. RESULTS The total number of analysed procedures in centre A was 350, during period I, and 270, during period II. In centre B, the number of analysed procedures was 611 and 740 during periods I and II, respectively, as presented in Table 2. Data analysed in this study are presented as follows: (1) Normalised whole-body doses from ED and TLD per units activity for centre A for periods I and II, in Figures 1, 2, 3 and 4, respectively. (2) Normalised whole-body doses from ED and TLD per units activity for centre B for periods I and II, in Figures 5, 6, 7 and 8, respectively. (3) Normalised extremity doses per unit activity, for centre B for periods I and II, in Figures 9 and 10, respectively. A correction factor of 6 for the estimation of extremity doses is used in this study. Cumulative doses for periods I and II and total activities for centres A and B are presented in Tables 3 and 4. Estimation of the maximal annual effective dose has been obtained on an individual worst-case scenario, contrary to the estimation of an average annual effective dose obtained based on average staff doses. Linear extrapolation of the maximal and average individual dose values for a 7-month period was used for annual dose estimation. The results are shown in Table 5. According to TLD reading, the doses per procedure in terms of Hp(10) were 3.9–5.7 and 4.2– 7 mSv in centre A during periods I and Table 2. Workload and staff members involved in PET/CT practice in two centres. Centre A Period Time period (months) Number of procedure analysed Number of staff analysed (total number involved in PET/CT)
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I
II
Centre B I
II
7 7 7 7 350 270 611 740 4 (8) 6 (6)
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steps in the patient management. PET/CT scanning is performed 3 d week21 with 12 procedures d21. On an average, one technologist takes care of two patients per day. In this centre, physicians routinely do not perform any activity that may result in the exposure to the ionising radiation. Whereas an automatic dispensing system is used in centre A, in centre B, only a semi-automatic dispensing system was available. Furthermore, the workload in this centre has been rather low and so the number of patients examined was not sufficient for staff to become experienced. To improve the working practice in centre B, training was performed according to recommendations for the training of NM staff(24, 28) that are required to optimise the working practice in January 2012. The activities included the use of nonradioactive material by the staff members in order to gain more experience and routine. This action improved the efficiency and led to a time reduction up to 32 % during the dispensing phase, 50 % during the injection phase and nearly 40 % during the removal of butterfly needle. Concerning radiation protection tools in both centres, radiation work is performed in the dedicated facilities using protection tools that have an impact on the radiation dose levels. Staff in centre B uses a semiautomatic dispensing system (LYNAX, PT317R2). Other protective tools such as 10-cm thick lead bricks, lead glass, lead transport containers and 30-cm long forceps for radionuclide manipulation are also used. In both centres, a 4.5-cm thick tungsten vial shield and syringe shield (0.8 cm of tungsten) were applied, but after implementation of the system for automated dispensing and injection they become redundant in centre A. Latex gloves are routinely used in both centres. In both facilities, CT scans are performed from the well-protected control room, which makes the positron-emitting radionuclide the major contributor to the radiation dose of the personnel(23, 29).
V. ANTIC ET AL.
Figure 2. Normalised Hp(10) per unit activity per month for staff member in centre A with system for automatic dispensing and injection using ED.
II and in centre B, the Hp(10) values were 7–11 and 5– 6 mSv in periods I and II, respectively. The extremity dose in terms of Hp(0.07) in centre B was in the range of 100 –630 mSv procedure21 in period I and 30 –160 mSv procedure21 in period II. According to ED reading, the doses per procedure in terms of Hp(10) were in the range of 0.2–1.8 and 0.1 –0.9 mSv in centre A during periods I and II and in centre B, the Hp(10) values were in the range of 0.7–1.3 and 0.5 –0.8 mSv, respectively. DISCUSSION The use of PET/CT is increasing worldwide which has raised concerns regarding staff radiation exposure
Figure 3. Normalised Hp(10) per unit activity per month for staff member in centre A without system for automatic dispensing and injection measured using TLD.
Figure 4. Normalised Hp(10) per unit activity per month for staff member in centre A with system for automatic dispensing and injection using TLD.
involved in these procedures. In PET facilities, the dose is higher than in other types of NM, owing to the high energy of annihilation photons and the fact that the use of protective aprons is not feasible(9). Compared with general NM procedures, exposure of PET/CT technologists to the radiation dose is higher and is estimated to be 771 mSv quarter21, compared with 524 mSv in conventional NM for the same period(18). The radiation dose to the personnel is caused mainly from handling the radiopharmaceuticals ( preparation of the syringe and withdrawal, intravenous injection, waste handling, etc.) and from close contact with the patient. In general, difficulties in comparing doses between different PET/CT facilities arise from variations in facility infrastructure, protocol, acquisition time, radionuclide activity used or
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Figure 1. Normalised Hp(10) per unit activity per month for staff member in centre A without system for automatic dispensing and injection measured using ED.
OCCUPATIONAL RADIATION DOSE IN PET/CT
Figure 6. Normalised Hp(10) per unit activity per month for staff member in centre B after work process optimisation measured using ED.
protective tools; however, the comparison of the dose resulting from an entire procedure can provide a valuable information on the local PET/CT practice. Typical annual dose levels are extrapolated according to the average cumulative dose in centres A and B during period I/II. The typical annual values can be used for the estimation of local reference levels. The estimated annual doses for staff in terms of Hp(10) at centres A and B are well in accordance with the prescribed dose constrains derived in other PET/CT centres, which are set to be 3–5 mSv y21(9) for Hp(10) as shown in Table 5. The estimated maximal annual whole-body dose was 3.4 mSv ( period I) and 3.2 mSv ( period II) in
Figure 7. Normalised Hp(10) per unit activity per month for staff member in centre B before work process optimisation measured using TLD.
Figure 8. Normalised Hp(10) per unit activity per month for staff member in centre B after work process optimisation measured using TLD.
centre A, according to TLD measurements. Similar values in centre B were 2.0 mSv ( period I) and 1.2 mSv ( period II). This is lower than the prescribed annual dose limit of 20 mSv. The maximal annual whole-body doses for technologists reported by other studies are typically similar or larger and range from 2 –3 up to 12 mSv(4, 9, 12, 30). It is important to note that the distribution of the dose across the hand may vary significantly for one operator but also among different operators performing the same type of procedure(31). The appropriate position of the dosemeter for monitoring of the extremities is at the base of the index finger of the nondominant hand with its sensitive part oriented towards the palm side(17), but according to the
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Figure 5. Normalised Hp(10) per unit activity per month for staff member in centre B before work process optimisation measured using ED.
V. ANTIC ET AL.
Figure 10. Normalised Hp(0.07) per unit activity per month for staff member in centre B after work process optimisation. Table 3. Cumulative doses and total activities in centre A for a 7-month period. Hp(10)TLD (mSv) Period Physician 1 Physician 2 Technologist Radiochemist
Hp(10)-ED (mSv)
A (GBq)
I
II
I
II
I
II
1.5 1.4 2.0 1.4
1.3 1.2 1.9 1.2
0.2 0.08 0.6 0.10
0.03 0.03 0.2 0.03
86 86 86 86
66 66 66 66
ORAMED study(15, 17) it is not the place with a maximum dose level; therefore, appropriate correction factors should be used. Reported ratios of the
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Figure 9. Normalised Hp(0.07) per unit activity per month for staff member in centre B before work process optimisation.
maximum dose to the dose at other positions (wrist, base of the index, base of the ring and tip of the index finger) are in the range of 2–93. The ORAMED study(15, 17) suggested the correction factor of 6 for the estimation of the maximal extremity dose if TLD is located at the base of the index finger of the dominant hand, as found in this study. As presented in Table 6 and revealed from this study in Figures 9 and 10, the dose values, in particular the extremity dose values can vary up to few orders of magnitude, which is related to different working habits and level of protection used. However, the reduction of exposure time and use of appropriate shielding in all procedures can reduce the radiation dose to staff handling the FDG(5), which is also confirmed by this study from Table 4 and Figures 9 and 10. Here, it is important to note the high values in Figures 9 and 10 in March and April, which can be attributed to dosemeter contamination, and is not here further analysed. Following implementation of an automatic dispenser, a cumulative dose reduction (from TLD measurements) in terms of Hp(10) is 12 % in centre A on an annual basis. The estimated reduction of typical annual whole-body dose in centre B, also based on TLD, is nearly 32 %. The corresponding typical annual dose values in terms of Hp(0.07) were 45 and 15 mSv. Therefore, the achieved dose reduction was 67 %. In addition, one must be aware of potential technical problems during syringe filing, disconnection from shielding, expelling air or difficulties with syringe interlocking that may increase the duration of injection. The duration of each step varies from technologist to technologist and depends also on the patient’s individual characteristics. Thus, more suitable parameters for comparison of PET/CT practice would be normalised dose per unit injected activity in units mSv GBq21, as presented in Table 6 and Figures 1–10. The mean dose values per unit activity obtained in this work are well in line with the results of similar studies, as presented in Table 6. However, the higher value of Hp(10) per unit administrated activity and per procedure in centre B in period I (Figures 5 and 7) had required particular attention and development of suitable strategies for optimisation of practice. In period II, after the training, the technologists become faster and more efficient in handling radiopharmaceuticals in phases of dispensing and injection. This action leads to reduction of individual normalised dose per unit activity up to 52 % in terms of Hp(10) and up to 92 % in terms of Hp(0.07) per activity. Even more significant dose reduction in terms of Hp(0.07) of 97 % was recently reported if an automated manipulation system is used(37). Unfortunately, extremity dosemeters were not available at centre A, and therefore it was not possible to assess the impact of the automatic dispenser on the finger dose.
OCCUPATIONAL RADIATION DOSE IN PET/CT Table 4. Cumulative doses and total activities in centre B for a 7-month period. Hp(10)-TLD (mSv) Period
II
I
II
I
II
I
II
0.8 1.0 1.2 0.8 1.1 0.9
0.7 0.7 0.6 0.6 0.7 0.7
0.13 0.13 0.11 0.08 0.10 0.068
0.08 0.11 0.11 0.06 0.08 0.11
15 36 14 11 62 18
19 7 6 11 5 5
23 23 26 26 25 24
28 34 30 24 27 30
Centre A (mSv)
Hp(10)TLD Hp(10)-ED Hp(0.07)
I
A (GBq)
I
Table 5. Estimated typical (the maximal values are shown in italics) annual dose.
Period
Hp(0.07) (mSv)
II
2.7 (3.4) 2.35 (3.2)
Centre B (mSv) I
II
1.6 (2.0)
1.1 (1.2)
0.43 (1.1) 0.14 (0.42) 0.17 (0.20) 0.15 (0.18) — — 45 (106) 15 (33)
Contrary to great impact to extremity doses, a system for automatic dispensing can help in reducing the whole-body dose up to 20 % as previously reported(37). According to the dose from ED per unit activity in centre A, individual dose reduction was from 50 to 77 %, but due to the fact that staff members in centre A were also involved in other NM imaging modalities, a significant dose reduction was not detected. It is important to note that ED was worn only at PET/CT modality and according to assessed doses for staff members who do not participate in PET/CT activity it can be assumed that PET/ CT practice dominantly contribute to the total dose. One should note that the difference in dose assessment using TLD and ED is large. This may be attributed to background radiation and the fact that ED is used only during PET/CT activities, involving small workload and a small portion of the entire working time. Nevertheless, it is very important to provide complete individual monitoring for the staff involved in PET/CT modality in both centres, including extremity monitors and whole-body monitors dedicated to PET activities. Whole-body dose per procedure was higher in centre B, during period I, but, in period II normalised whole-body doses in two centres were nearly the same (+1 mSv procedure21) if measured using TLD. According to TLD readings, there was no significant dose reduction per procedure in centre A, as staff members work on other NM modalities as mentioned above. However, dose reduction per procedure in
centre A assessed using ED was up to 77 %, whereas in centre B the dose reduction was up to 47 %. As EDs in centre A were worn only during PET studies, the observed dose reduction could be attributed to improvement of PET practice following training activities. Another recent study revealed that wholebody staff dose can be reduced from 9.5 to 4.8 mSv procedure21 as a result of optimisation(36) which is in line with this study. The workload in both PET/CT facilities in Serbia is not large; however, increase is expected in the future. Inevitably, the increased demand of PET studies would result in the increased staff exposure. With the measured maximal whole-body doses per procedure of 7 and 6 mSv in two centres, during period II, the whole-body annual dose limit of 20 mSv can be reached after handling 2860 and 3330 patients in centres A and B, respectively. At present, the annual number of patients is much lower (2000 in both centres, in total). The maximal measured Hp(0.07) per procedure during period II was 160 mSv, somewhat lower and comparable to the published data for the same type of practice(6). Therefore, centre B can perform nearly 3100 procedures and still keep the extremity dose ,500 mSv. As individual doses are influenced by the composition of the team, annual collective doses based on TLD readings were assessed. In centre A, it was 11 and 9 man mSv, in two periods, respectively, while in centre B, the corresponding values were 10 and 7 man mSv. From these numbers and Figures 1 – 8, it is clear that staff in centre B are equally exposed to radiation, while in centre A there is one staff member (technologist) who is receiving the most of the dose. The observed reduction of the collective dose in centre Awas 11, and 31 % in centre B. Collective dose per unit administered activity during periods I and II were 72 and 83 man mSv GBq21 in centre A and 39 and 22 man mSv GBq21 in centre B in both periods. These values again represent centre’s work organisation and optimisation. Higher values in centre A are not reflecting the optimised work practice, apart from the installed automated dispensing and injection system. In period II, in centre A, higher dose
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Technologist 1 Technologist 2 Technologist 3 Technologist 4 Technologist 5 Technologist 6
Hp(10)-ED (mSv)
V. ANTIC ET AL. Table 6. Comparison of results of the present study with the results of similar studies in terms of whole-body dose per procedure and normalised whole-body and extremity dose per unit administrated activity (Hp(10)/A and Hp(0.07)/A). Hp(10)/ procedure (mSv)
Hp(0.07)/A (mSv GBq21)
Automatic dispenser
Automatic injector
Reference
1.3–13 — 14–25 12 17 8.92 17 8.99 46 — 1.6–9.1 1.9–6.8 — 17–19 21–26
407– 419 100– 4430 — — — 340– 450 — 750– 1200 — 1800– 3000 — — — — 170– 680
No No No No No Semi-automatic naa Semi-automatic naa No naa naa naa Automated Semi-automated
No No No No No No naa Yes naa No No naa, b No Yes No
(5) (15, 17) (9) (32) (33) (4, 12) (30) (6) (34) (7) (35) (2) (36) This workc This workd
a
Information is not available. Monitored staff does not perform this operation. c Centre A, period II (TLD). d Centre B, period II (TLD). b
levels were noted, stressing the importance of optimisation of practice even if an automated dispensing system is used. On the other hand, values in centre B are showing importance of staff rotation. The collective dose per unit administered activity is 43 % lower in period II than in those period I. This means that after the optimisation of the work practice in centre B, staff members become more efficient as a team. The study has certain limitations. First, extremity dosimetry was available only in one centre. Secondly, contribution of different phases of radiopharmaceutical manipulation was not taken into account and in some cases, even contribution of other NM modalities. Thus, to further optimise PET/CT practice in these two centres, detailed measurements that can identify the phases where doses are high are indicated. CONCLUSION PET/CT requires special concern regarding occupational radiation protection. The level of whole-body and finger doses for technologists in the two PET/CT facilities in Serbia is presented. Although the individual doses are within the recommended regulatory limits, the increase in the workload would result in higher staff doses. Thus, an effort must be made to review the working procedure and reduce the radiation dose in both centres. The practice in both centres should be further investigated and appropriate protective measures subsequently be applied to reduce both whole-body and extremity doses as low as reasonably achievable.
FUNDING This work was supported by the Ministry of Education and Science of the Republic of Serbia (grant agreements: 43009, 171002 and 43002).
REFERENCES 1. Rohren, E. M., Turkington, T. G. and Coleman, E. Clinical applications of PET in oncology. Radiology 231, 305– 332 (2004). 2. Kumar, S., Pandey, A. K., Sharma, P., Shamim, S. A., Malhotra, A. and Kumar, R. Instantaneous exposure to nuclear medicine staff involved in PET-CT imaging in developing countries: experience from a tertiary care centre in India. Jpn J. Radiol. 30, 291– 295 (2012). 3. Dalianis, K., Malamitsia, J., Gogoua, L., Pagoua, M., Efthimiadoua, R., Andreoua, J., Louizı¨b, A. and Georgioub, E. Dosimetric evaluation of the staff working in a PET/CT department. Nucl. Instrum. Methods Phys. Res. A 569, 548– 550 (2006). 4. Demir, M., Demir, B., Yas¸ar, D., Sayman, H., Halac, ¨ zcan, K. and Uslu, I. Radiation doses M., Ahmed, A., O to technologists working with 18F-FDG in a PET center with high patient capacity. Nukleonika 55, 107–112 (2010). 5. Kopec, R., Budzanowski, M., Budzynska, A., Czepczynski, R., Dziuk, M., Sowinski, J. and Wyszomirska, A. On the relationship between whole body, extremity and eye lens doses for medical staff in the preparation and application of radiopharmaceuticals in nuclear medicine. Radiat. Meas. 46, 1295–1298 (2011).
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— — — 5.9 6.5 4.6 8.9 3.1 17 4 –5 — 0.6–2.1 0.9–3.2 4.2–7 5 –6
Hp(10)/A (mSv GBq21)
OCCUPATIONAL RADIATION DOSE IN PET/CT 22. Wrzesie´n, M., Olszewski, J. and Jankowski, J. Hand exposure to ionising radiation of nuclear medicine workers. Radiat. Prot. Dosim. 130, 325– 330 (2008). 23. Madsen, M. T., Anderson, J. A., Halama, J. R., Kleck, J., Simpkin, D. J., Votaw, J. R., Wendt, R. E., Williams, L. E. and Yester, M. V. AAPM task group 108: PET and PET/CT shielding requirements. Med. Phys. 33(1), 4 –15 (2006). 24. The European Association of Nuclear Medicine. Best Practice in Nuclear Medicine, Part 1 A Technologist’s Guide. European Association of Nuclear Medicine (2006). 25. The European Association of Nuclear Medicine. Principles and Practice of PET/CT, Part 1: A Technologist’s Guide. European Association of Nuclear Medicine (2010). 26. International Atomic Energy Agency. Radiation Protection and Safety of Radiation Sources: International Basic Safety Standards, Interim Edition. International Atomic Energy Agency (2011). 27. Jankowski, J., Olszewski, J. and Kluska, K. Distribution of equivalent doses to skin of the hands of nuclear medicine personnel. Radiat. Prot. Dosim. 106, 177– 180 (2003). 28. International Atomic Energy Agency. Safety Reports Series No.40: applying radiation safety standards in nuclear medicine. IAEA (2005). 29. Antic, V., Stankovic´, K., Vujisic´, M. and Osmokrovic´, P. Comparison of various methods for designing the shielding from ionising radiation at PET-CT installations. Radiat. Prot. Dosim. 154, 245– 249 (2013). 30. Lineman, H., Will, E. and Beuthien-Baumann, B. Investigations of radiation exposure of the medical personnel during F-18-FDG PET studies. Nuklearmedizin 39, 77–81 (2000). 31. Zeff, B. W. and Yester, M. V. Patient self-attenuation and technologist dose in positron emission tomography. Med. Phys. 32, 861– 865 (2005). 32. Donadille, L., Carinou, E., Ginjaume, M., Jankowski, J., Rimpler, A., Sans Merce, M. and Vanhavere, F. An overview of the use of extremity dosemeters in some European countries for medical applications. Radiat. Prot. Dosim. 131, 62– 66 (2008). 33. Chiesa, C., De Sanctis, V., Crippa, F., Schiavini, M., Fraigola, C. E., Bogni, A., Pascali, C., Decise, D., Marchesini, R. and Bombardieri, E. Radiation dose to technicians per nuclear medicine procedure: comparison between technetium-99 m, gallium-67 and iodine-131. Eur. J. Nucl. Med. 24, 1380–1389 (1997). 34. Benatar, N. A., Cronin, B. F. and O’Doherty, M. J. Radiation dose rates from patients undergoing PET: implications for technologists and waiting areas. Eur. J. Nucl. Med. 27, 583 –589 (2000). 35. Pant, G. S. and Senthamizhchelvan, S. Radiation exposure to staff in a PET/CT facility. Indian J. Nucl. Med. 21, 100–103 (2006). 36. Peet, D. J., Morton, R., Hussein, M., Alsafi, K. and Spyrou, N. Radiation protection in fixed PET/CT facilities-design and operation. Br. J. Radiol. 85, 643– 646 (2012). 37. Covens, P., Berus, D., Vanhavere, F. and Caveliers, V. The introduction of automated dispensing and injection during PET procedures: a step in the optimisation of extremity doses and whole-body doses of nuclear medicine staff. Radiat. Prot. Dosim. 140, 250–258 (2010).
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6. Guillet, B., Quentin, P., Waultier, S., Bourrelly, M., Pisano, P. and Mundler, O. Technologist radiation exposure in routine clinical practice with 18F-FDG PET. J. Nucl. Med. Technol. 33, 175– 179 (2005). 7. Leide-Svegborn, S. Radiation exposure of patients and personnel from a PET/CT procedure with 18F-FDG. Radiat. Prot. Dosim. 139, 208–213 (2010). 8. Cao, Z. J. et al. 18F protection issues: human and gcamera considerations. J. Nucl. Med. Technol. 31, 210 –215 (2003). 9. Seierstad, T., Stranden, E., Bjering, K., Evensen, M., Holt, A., Michalsen, H. M. and Wetteland, O. Doses to nuclear technicians in a dedicated PET/CT centre utilising 18F fluorodeoxyglucose (FDG). Radiat. Prot. Dosim. 123, 246– 249 (2007). 10. Vargas Castrilloon, S. and Cutanda Henriquez, F. A study on occupational exposure in a PET/CT facility. Radiat. Prot. Dosim. 147, 247–249 (2011). 11. Al-Haj, A. N., Lobriguito, A. M., Arafah, A. and Parker, R. Deriving staff and public doses in a PET/CT facility from measured radiation levels using thermoluminescent dosimetry. Radiat. Prot. Dosim. 144, 487 –491 (2011). 12. Demir, M., Demir, B., Sayman, H., Sager, S., Sabbir Ahmed, A. and Uslu, I. Radiation protection for accompanying person and radiation workers in PET/CT. Radiat. Prot. Dosim. 147, 528–532 (2011). 13. Sandouqa, A. S., Haddadin, I. M. and Abu-Khaled, Y. S. Hand equivalent doses of nuclear medicine staff in Jordan: preliminary experimental studies. Radiat. Meas. 46, 250–253 (2011). 14. Avila, O., Torres-Ulloaa, C. L., Medinac, L. A., Trujillo-Zamudioe, F. E., Gamboa-deBuenf, A. E., Buenfilc, A. E. and Brandanc, M. E. TL measurement of ambient dose at a Nuclear Medicine Department. Radiat. Meas. 46, 1843– 1846 (2011). 15. Carnicer, A. et al. The use of different types of thermoluminescent dosemeters to measure extremity doses in nuclear medicine. Radiat. Meas. 46, 1835–1838 (2011). 16. Sudbrock, F., Uhrhan, K., Rimpler, A. and Schicha, H. Dose and dose rate measurements for radiation exposure scenarios in nuclear medicine. Radiat. Meas. 46, 1303–1306 (2011). 17. Carnicer, A. et al. Hand exposure in diagnostic nuclear medicine with 18F- and 99mTc-labelled radiopharmaceuticals—results of the ORAMED project. Radiat. Meas. 46, 1277– 1282 (2011). 18. Roberts, F., Gunawardana, D. H., Pathmaraj, K., Wallace, A., U, P. L., Mi, T., Berlangieri, S. U., O’Keefe, G. J., Rowe, C. C. and Scott, A. M. Radiation dose to PET technologists and strategies to lower occupational exposure. J. Nucl. Med. Technol. 33, 44–47 (2005). 19. Quinn, B., Holahan, B., Aime, J., Humm, J., St Germain, J. and Dauer, L. T. Measured dose rate constant from oncology patients administered 18F for positron emission tomography. Med. Phys. 39(10), 6071–6079 (2012). 20. Chruscielewski, W., Olszewski, J., Jankowski, J. and Cygan, M. Hand exposure in nuclear medicine workers. Radiat. Prot. Dosim. 101, 229–232 (2002). 21. Vanhavere, F., Carinou, E., Donadille, L., Ginjaume, M., Jankowski, J., Rimpler, A. and Sans Merce, M. An overview of extremity dosimetry in medical applications. Radiat. Prot. Dosim. 129, 350–355 (2008).
doi:10.1093/rpd/ncu001
RADIATION EXPOSURE TO NUCLEAR MEDICINE STAFF INVOLVED IN PET/CT PRACTICE IN SERBIA V. Antic1, O. Ciraj-Bjelac2,*, J. Stankovic2, D. Arandjic2, N. Todorovic3 and S. Lucic4 1 Center for Nuclear Medicine, University Clinical Centre of Serbia, Belgrade, Serbia 2 Radiation Protection Laboratory, Vinca Institute of Nuclear Science, University of Belgrade, PO Box 522, Belgrade 11001, Serbia 3 Faculty of Science, Department of Physics, University of Novi Sad, Novi Sad, Serbia 4 Oncology Institute of Vojvodina, Sremska Kamenica, Novi Sad, Serbia
Received 25 March 2013; revised 23 December 2013; accepted 1 January 2014 The purpose of this work is to evaluate the radiation exposure to nuclear medicine (NM) staff in the two positron emission tomography-computed tomography centres in Serbia and to investigate the possibilities for dose reduction. Dose levels in terms of Hp(10) for whole body and Hp(0.07) for hands of NM staff were assessed using thermoluminescence and electronic personal dosemeters. The assessed doses per procedure in terms of Hp(10) were 4.2–7 and 5– 6 mSv, in two centres, respectively, whereas the extremity doses in terms of Hp(0.07) in one of the centres was 34–126 mSv procedure21. The whole-body doses per unit activity were 17– 19 and 21– 26 mSv GBq21 in two centres, respectively, and the normalised finger dose in one centre was 170– 680 mSv GBq21. The maximal estimated annual whole-body doses in two centres were 3.4 and 2.0 mSv, while the corresponding extremity dose in the later one was 45 mSv. Improvements as introduction of automatic dispensing system and injection and optimisation of working practice resulted in dose reduction ranging from 12 up to 67 %.
INTRODUCTION Positron emission tomography (PET) is a modern and non-invasive imaging modality that provides visual and semi-quantitative assessment of functioning of organs and tissues. Computed tomography (CT) is a non-invasive technology that gives the superior morphological image of the observed body region. Using a multimodal PET/CT, the anatomical and metabolic information is displayed in a combined image(1 – 3). The PET procedure involves the administration of the radiopharmaceuticals in the body. The most widely used radiopharmaceutical for clinical PET/CT applications is 18F-fluorodeoxyglucose (FDG)(1, 2). The radionuclide 18F used to label FDG is positron emitter (630 keV), producing high-energy annihilation photons of 511 keV, which causes a relatively high radiation exposure to nuclear medicine (NM) staff. The observed radiation dose is related to the amount of activity in the source and length of time of an individual exposure(4). PET/CT scanners have been commonly installed in the existing NM departments; however, the relatively long uptake phase, high-energy gamma radiation and manipulation of unsealed radiation sources (during dispensing and injection), has put a challenge to keep occupational whole-body and extremity doses as low as reasonable achievable. Many investigations regarding radiation protection of medical staff working in PET/CT departments were conducted worldwide(5 – 19). Some of the studies
indicated high radiation doses due to both radionuclide handling and the interaction with a patient after radionuclide administration(7, 8, 18). Indeed, the higher energy of radiation means that medical staff could receive a higher whole-body dose than those working only with conventional NM radionuclides. Manipulation of unsealed sources in NM, in particular those emitting beta radiation, involves high skin doses to the upper extremities during preparation and injection of the radiopharmaceuticals. Many studies indicated that local skin doses can surpass the annual dose limit of 500 mSv averaged over 1 cm2(20 – 22). Therefore, international investigations were directed to dosimetry for extremities in PET/CT practice(15, 17). Dose to the staff can be minimised in multiple ways, mainly by training them in applying basic radiation principles such as maintaining distance from the radiation source or patient (19, 23), performing operations in a shortest possible time(24) and using shielding (shielded dispensers, etc.) whenever practicable(18, 25). The occupational exposure in PET imaging can also be controlled by rotating the staff members in performing particular duties, avoiding the close contact with the radioactive source, using semi-automatic or automatic injector, video and audio monitoring and communicating with injected patients(6). The aim of the present work is to provide an overview and analyse the magnitude of radiation exposure in terms of whole-body and extremity doses to NM
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*Corresponding author: [email protected]
V. ANTIC ET AL.
staff working in PET/CT practice in Serbia, and accordingly, to discuss introduced methods for dose reduction as automated dispensing and injection system, and optimisation of routine working practice. MATERIALS AND METHODS
Dosimetry International Basic Safety Standards(26) recommends the use of personal dose equivalents Hp(0.07) for doses to the extremities, Hp(3) for doses to the lens of the eye and Hp(10) for doses to the whole body, as relevant operational quantities for individual monitoring of external radiation. Typically, a single whole-body dosemeter is used for individual monitoring of external radiation. However, several studies confirm that NM personnel should be equipped not only with wholebody dosemeters, but also with thermoluminescence dosemeter (TLD) for extremity monitoring(20, 22, 27). Staff in both PET/CT centres in Serbia is routinely monitored using TLDs and personal electronic dosemeters (EDs) worn at the chest level. TLD for extremity monitoring, DXT-100 ringlet, was inserted into a plastic ring holder, which was worn on the index finger base of the dominant hand of staff in one centre. The routine monitoring service is provided by accredited laboratories of Institute of occupational health: Belgrade, Serbia (for centre A) and Vinca Institute of Nuclear Sciences, Belgrade, Serbia (centre B), both using Harshaw 6600 readers. Calibration of dosemeters in terms of Hp(10) and Hp(0.07) was performed at Secondary Standard Dosimetry Laboratory of Vinca Institute of Nuclear Sciences, Belgrade, which is accredited to EN ISO/IEC 17025. The basic information on PET/CT units and dosemeters used in these institutions is summarised in Table 1.
A PET/CT procedure in both centres consists of multiple steps. The first step is the receipt of the radiopharmaceutical in the transport container. The FDG is further handled in the ‘hot’ laboratory, which includes measuring the delivered activity, calculating activity/time and dispensing of the multidose activity in the syringes for single injection, and subsequently the injection of radiopharmaceuticals to the patients. The last step includes the time spent in collection and escorting the patients to the imaging room, positioning and, after image acquisition, escorting of patients out of the NM department. All these steps contribute to the dose to NM staff, depending on the facility design and level of radiation protection applied. In centre A, two different teams are taking care of patients. Approximately 10 patients are examined per day and each team is working 1 d week21 on the PET/CT modality. Each team consists of two physicians, a technologist and a radiochemist. In 2011, before the introduction of an s for dispensing and injection into the practice, the radiochemist was responsible for manual radiopharmaceutical dispensing and the technologist for injection and patient escorting and positioning. In this period, physicians were present during the injection phase supervising the whole procedure. When the automated system for dispensing and injection was introduced in October 2011 (MEDRAD, IntegoTM PET Infusion System), physicians have become equally involved in the activities related to the dispensing and injection of radiopharmaceuticals as other two team members. Still, the technologist remains to be the person most frequently nearest to the patient. It is important to note that in both periods during injection of the radiopharmaceuticals the whole team was present in the room, sharing the responsibility for patient management from the beginning to the end. Practice in centre B is different. There are six technologists exclusively working at PET/CT facility. In this centre, staff is rotationally changing in performing different duties. One technologist takes care of one patient at the time, performing all above-mentioned
Table 1. The basic information about PET/CT centres in Serbia. Name of institution
Institute for Oncology Sremska Kamenica Centre A
PET/CT unit (manufacturer/model) Radiopharmaceutical Personal dosemeters (whole body) Personal dosemeters (extremities) Personal EDs (whole body)
Siemens Biograph True Point 40/64 F-FDG (multidose vial) Harshaw TLD-100H Not available Mirion DMC 2000XB
18
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National PET Centre in Clinical Centre of Serbia Centre B Siemens Biograph True Point 40/64 18 F-FDG (multidose vial) Harshaw TLD-100 Harshaw DXT-100 Mirion DMC2000X, DMC2000XG
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PET/CT practice in Serbia is currently conducted in two medical centres. Both sites are using the same model of PET/CT unit and 18F-FDG as the only radiopharmaceutical. According to data retrieved from administration from both centres, 2000 procedures are performed annually in Serbia.
Workpractice
OCCUPATIONAL RADIATION DOSE IN PET/CT
Data collection Data about the occupational dose to NM staff involved in PET/CT practice were collected from both institutions in Serbia in the period 2011– 12. In this work, the doses were analysed for two different periods: (1) Period I: Without the automated system for dispensing and injection in centre A and before the training in centre B (data were available from March to September 2011); (2) Period II: With the automated system for dispensing and injection in centre A and after the training in centre B (data were available from March to September 2012). Data were obtained for 10 staff members involved in PET/CT practice: two physicians, one technologist
and one radiochemist from centre A and six technologists from centre B. Data collection was performed in both centres for periods I and II in terms of the number of procedures per month, administered activity per each procedure, Hp(10) per day using ED, Hp(0.07) per month measured using TLD (only in centre B) and Hp(10) per month measured using TLD. The measured dose values, both in terms of Hp(10) and Hp(0.07) were normalised to the total manipulated activity. In addition, the total maximal and typical annual dose were estimated based on the information about cumulative doses during 7 months. RESULTS The total number of analysed procedures in centre A was 350, during period I, and 270, during period II. In centre B, the number of analysed procedures was 611 and 740 during periods I and II, respectively, as presented in Table 2. Data analysed in this study are presented as follows: (1) Normalised whole-body doses from ED and TLD per units activity for centre A for periods I and II, in Figures 1, 2, 3 and 4, respectively. (2) Normalised whole-body doses from ED and TLD per units activity for centre B for periods I and II, in Figures 5, 6, 7 and 8, respectively. (3) Normalised extremity doses per unit activity, for centre B for periods I and II, in Figures 9 and 10, respectively. A correction factor of 6 for the estimation of extremity doses is used in this study. Cumulative doses for periods I and II and total activities for centres A and B are presented in Tables 3 and 4. Estimation of the maximal annual effective dose has been obtained on an individual worst-case scenario, contrary to the estimation of an average annual effective dose obtained based on average staff doses. Linear extrapolation of the maximal and average individual dose values for a 7-month period was used for annual dose estimation. The results are shown in Table 5. According to TLD reading, the doses per procedure in terms of Hp(10) were 3.9–5.7 and 4.2– 7 mSv in centre A during periods I and Table 2. Workload and staff members involved in PET/CT practice in two centres. Centre A Period Time period (months) Number of procedure analysed Number of staff analysed (total number involved in PET/CT)
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I
II
Centre B I
II
7 7 7 7 350 270 611 740 4 (8) 6 (6)
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steps in the patient management. PET/CT scanning is performed 3 d week21 with 12 procedures d21. On an average, one technologist takes care of two patients per day. In this centre, physicians routinely do not perform any activity that may result in the exposure to the ionising radiation. Whereas an automatic dispensing system is used in centre A, in centre B, only a semi-automatic dispensing system was available. Furthermore, the workload in this centre has been rather low and so the number of patients examined was not sufficient for staff to become experienced. To improve the working practice in centre B, training was performed according to recommendations for the training of NM staff(24, 28) that are required to optimise the working practice in January 2012. The activities included the use of nonradioactive material by the staff members in order to gain more experience and routine. This action improved the efficiency and led to a time reduction up to 32 % during the dispensing phase, 50 % during the injection phase and nearly 40 % during the removal of butterfly needle. Concerning radiation protection tools in both centres, radiation work is performed in the dedicated facilities using protection tools that have an impact on the radiation dose levels. Staff in centre B uses a semiautomatic dispensing system (LYNAX, PT317R2). Other protective tools such as 10-cm thick lead bricks, lead glass, lead transport containers and 30-cm long forceps for radionuclide manipulation are also used. In both centres, a 4.5-cm thick tungsten vial shield and syringe shield (0.8 cm of tungsten) were applied, but after implementation of the system for automated dispensing and injection they become redundant in centre A. Latex gloves are routinely used in both centres. In both facilities, CT scans are performed from the well-protected control room, which makes the positron-emitting radionuclide the major contributor to the radiation dose of the personnel(23, 29).
V. ANTIC ET AL.
Figure 2. Normalised Hp(10) per unit activity per month for staff member in centre A with system for automatic dispensing and injection using ED.
II and in centre B, the Hp(10) values were 7–11 and 5– 6 mSv in periods I and II, respectively. The extremity dose in terms of Hp(0.07) in centre B was in the range of 100 –630 mSv procedure21 in period I and 30 –160 mSv procedure21 in period II. According to ED reading, the doses per procedure in terms of Hp(10) were in the range of 0.2–1.8 and 0.1 –0.9 mSv in centre A during periods I and II and in centre B, the Hp(10) values were in the range of 0.7–1.3 and 0.5 –0.8 mSv, respectively. DISCUSSION The use of PET/CT is increasing worldwide which has raised concerns regarding staff radiation exposure
Figure 3. Normalised Hp(10) per unit activity per month for staff member in centre A without system for automatic dispensing and injection measured using TLD.
Figure 4. Normalised Hp(10) per unit activity per month for staff member in centre A with system for automatic dispensing and injection using TLD.
involved in these procedures. In PET facilities, the dose is higher than in other types of NM, owing to the high energy of annihilation photons and the fact that the use of protective aprons is not feasible(9). Compared with general NM procedures, exposure of PET/CT technologists to the radiation dose is higher and is estimated to be 771 mSv quarter21, compared with 524 mSv in conventional NM for the same period(18). The radiation dose to the personnel is caused mainly from handling the radiopharmaceuticals ( preparation of the syringe and withdrawal, intravenous injection, waste handling, etc.) and from close contact with the patient. In general, difficulties in comparing doses between different PET/CT facilities arise from variations in facility infrastructure, protocol, acquisition time, radionuclide activity used or
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Figure 1. Normalised Hp(10) per unit activity per month for staff member in centre A without system for automatic dispensing and injection measured using ED.
OCCUPATIONAL RADIATION DOSE IN PET/CT
Figure 6. Normalised Hp(10) per unit activity per month for staff member in centre B after work process optimisation measured using ED.
protective tools; however, the comparison of the dose resulting from an entire procedure can provide a valuable information on the local PET/CT practice. Typical annual dose levels are extrapolated according to the average cumulative dose in centres A and B during period I/II. The typical annual values can be used for the estimation of local reference levels. The estimated annual doses for staff in terms of Hp(10) at centres A and B are well in accordance with the prescribed dose constrains derived in other PET/CT centres, which are set to be 3–5 mSv y21(9) for Hp(10) as shown in Table 5. The estimated maximal annual whole-body dose was 3.4 mSv ( period I) and 3.2 mSv ( period II) in
Figure 7. Normalised Hp(10) per unit activity per month for staff member in centre B before work process optimisation measured using TLD.
Figure 8. Normalised Hp(10) per unit activity per month for staff member in centre B after work process optimisation measured using TLD.
centre A, according to TLD measurements. Similar values in centre B were 2.0 mSv ( period I) and 1.2 mSv ( period II). This is lower than the prescribed annual dose limit of 20 mSv. The maximal annual whole-body doses for technologists reported by other studies are typically similar or larger and range from 2 –3 up to 12 mSv(4, 9, 12, 30). It is important to note that the distribution of the dose across the hand may vary significantly for one operator but also among different operators performing the same type of procedure(31). The appropriate position of the dosemeter for monitoring of the extremities is at the base of the index finger of the nondominant hand with its sensitive part oriented towards the palm side(17), but according to the
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Figure 5. Normalised Hp(10) per unit activity per month for staff member in centre B before work process optimisation measured using ED.
V. ANTIC ET AL.
Figure 10. Normalised Hp(0.07) per unit activity per month for staff member in centre B after work process optimisation. Table 3. Cumulative doses and total activities in centre A for a 7-month period. Hp(10)TLD (mSv) Period Physician 1 Physician 2 Technologist Radiochemist
Hp(10)-ED (mSv)
A (GBq)
I
II
I
II
I
II
1.5 1.4 2.0 1.4
1.3 1.2 1.9 1.2
0.2 0.08 0.6 0.10
0.03 0.03 0.2 0.03
86 86 86 86
66 66 66 66
ORAMED study(15, 17) it is not the place with a maximum dose level; therefore, appropriate correction factors should be used. Reported ratios of the
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Figure 9. Normalised Hp(0.07) per unit activity per month for staff member in centre B before work process optimisation.
maximum dose to the dose at other positions (wrist, base of the index, base of the ring and tip of the index finger) are in the range of 2–93. The ORAMED study(15, 17) suggested the correction factor of 6 for the estimation of the maximal extremity dose if TLD is located at the base of the index finger of the dominant hand, as found in this study. As presented in Table 6 and revealed from this study in Figures 9 and 10, the dose values, in particular the extremity dose values can vary up to few orders of magnitude, which is related to different working habits and level of protection used. However, the reduction of exposure time and use of appropriate shielding in all procedures can reduce the radiation dose to staff handling the FDG(5), which is also confirmed by this study from Table 4 and Figures 9 and 10. Here, it is important to note the high values in Figures 9 and 10 in March and April, which can be attributed to dosemeter contamination, and is not here further analysed. Following implementation of an automatic dispenser, a cumulative dose reduction (from TLD measurements) in terms of Hp(10) is 12 % in centre A on an annual basis. The estimated reduction of typical annual whole-body dose in centre B, also based on TLD, is nearly 32 %. The corresponding typical annual dose values in terms of Hp(0.07) were 45 and 15 mSv. Therefore, the achieved dose reduction was 67 %. In addition, one must be aware of potential technical problems during syringe filing, disconnection from shielding, expelling air or difficulties with syringe interlocking that may increase the duration of injection. The duration of each step varies from technologist to technologist and depends also on the patient’s individual characteristics. Thus, more suitable parameters for comparison of PET/CT practice would be normalised dose per unit injected activity in units mSv GBq21, as presented in Table 6 and Figures 1–10. The mean dose values per unit activity obtained in this work are well in line with the results of similar studies, as presented in Table 6. However, the higher value of Hp(10) per unit administrated activity and per procedure in centre B in period I (Figures 5 and 7) had required particular attention and development of suitable strategies for optimisation of practice. In period II, after the training, the technologists become faster and more efficient in handling radiopharmaceuticals in phases of dispensing and injection. This action leads to reduction of individual normalised dose per unit activity up to 52 % in terms of Hp(10) and up to 92 % in terms of Hp(0.07) per activity. Even more significant dose reduction in terms of Hp(0.07) of 97 % was recently reported if an automated manipulation system is used(37). Unfortunately, extremity dosemeters were not available at centre A, and therefore it was not possible to assess the impact of the automatic dispenser on the finger dose.
OCCUPATIONAL RADIATION DOSE IN PET/CT Table 4. Cumulative doses and total activities in centre B for a 7-month period. Hp(10)-TLD (mSv) Period
II
I
II
I
II
I
II
0.8 1.0 1.2 0.8 1.1 0.9
0.7 0.7 0.6 0.6 0.7 0.7
0.13 0.13 0.11 0.08 0.10 0.068
0.08 0.11 0.11 0.06 0.08 0.11
15 36 14 11 62 18
19 7 6 11 5 5
23 23 26 26 25 24
28 34 30 24 27 30
Centre A (mSv)
Hp(10)TLD Hp(10)-ED Hp(0.07)
I
A (GBq)
I
Table 5. Estimated typical (the maximal values are shown in italics) annual dose.
Period
Hp(0.07) (mSv)
II
2.7 (3.4) 2.35 (3.2)
Centre B (mSv) I
II
1.6 (2.0)
1.1 (1.2)
0.43 (1.1) 0.14 (0.42) 0.17 (0.20) 0.15 (0.18) — — 45 (106) 15 (33)
Contrary to great impact to extremity doses, a system for automatic dispensing can help in reducing the whole-body dose up to 20 % as previously reported(37). According to the dose from ED per unit activity in centre A, individual dose reduction was from 50 to 77 %, but due to the fact that staff members in centre A were also involved in other NM imaging modalities, a significant dose reduction was not detected. It is important to note that ED was worn only at PET/CT modality and according to assessed doses for staff members who do not participate in PET/CT activity it can be assumed that PET/ CT practice dominantly contribute to the total dose. One should note that the difference in dose assessment using TLD and ED is large. This may be attributed to background radiation and the fact that ED is used only during PET/CT activities, involving small workload and a small portion of the entire working time. Nevertheless, it is very important to provide complete individual monitoring for the staff involved in PET/CT modality in both centres, including extremity monitors and whole-body monitors dedicated to PET activities. Whole-body dose per procedure was higher in centre B, during period I, but, in period II normalised whole-body doses in two centres were nearly the same (+1 mSv procedure21) if measured using TLD. According to TLD readings, there was no significant dose reduction per procedure in centre A, as staff members work on other NM modalities as mentioned above. However, dose reduction per procedure in
centre A assessed using ED was up to 77 %, whereas in centre B the dose reduction was up to 47 %. As EDs in centre A were worn only during PET studies, the observed dose reduction could be attributed to improvement of PET practice following training activities. Another recent study revealed that wholebody staff dose can be reduced from 9.5 to 4.8 mSv procedure21 as a result of optimisation(36) which is in line with this study. The workload in both PET/CT facilities in Serbia is not large; however, increase is expected in the future. Inevitably, the increased demand of PET studies would result in the increased staff exposure. With the measured maximal whole-body doses per procedure of 7 and 6 mSv in two centres, during period II, the whole-body annual dose limit of 20 mSv can be reached after handling 2860 and 3330 patients in centres A and B, respectively. At present, the annual number of patients is much lower (2000 in both centres, in total). The maximal measured Hp(0.07) per procedure during period II was 160 mSv, somewhat lower and comparable to the published data for the same type of practice(6). Therefore, centre B can perform nearly 3100 procedures and still keep the extremity dose ,500 mSv. As individual doses are influenced by the composition of the team, annual collective doses based on TLD readings were assessed. In centre A, it was 11 and 9 man mSv, in two periods, respectively, while in centre B, the corresponding values were 10 and 7 man mSv. From these numbers and Figures 1 – 8, it is clear that staff in centre B are equally exposed to radiation, while in centre A there is one staff member (technologist) who is receiving the most of the dose. The observed reduction of the collective dose in centre Awas 11, and 31 % in centre B. Collective dose per unit administered activity during periods I and II were 72 and 83 man mSv GBq21 in centre A and 39 and 22 man mSv GBq21 in centre B in both periods. These values again represent centre’s work organisation and optimisation. Higher values in centre A are not reflecting the optimised work practice, apart from the installed automated dispensing and injection system. In period II, in centre A, higher dose
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Technologist 1 Technologist 2 Technologist 3 Technologist 4 Technologist 5 Technologist 6
Hp(10)-ED (mSv)
V. ANTIC ET AL. Table 6. Comparison of results of the present study with the results of similar studies in terms of whole-body dose per procedure and normalised whole-body and extremity dose per unit administrated activity (Hp(10)/A and Hp(0.07)/A). Hp(10)/ procedure (mSv)
Hp(0.07)/A (mSv GBq21)
Automatic dispenser
Automatic injector
Reference
1.3–13 — 14–25 12 17 8.92 17 8.99 46 — 1.6–9.1 1.9–6.8 — 17–19 21–26
407– 419 100– 4430 — — — 340– 450 — 750– 1200 — 1800– 3000 — — — — 170– 680
No No No No No Semi-automatic naa Semi-automatic naa No naa naa naa Automated Semi-automated
No No No No No No naa Yes naa No No naa, b No Yes No
(5) (15, 17) (9) (32) (33) (4, 12) (30) (6) (34) (7) (35) (2) (36) This workc This workd
a
Information is not available. Monitored staff does not perform this operation. c Centre A, period II (TLD). d Centre B, period II (TLD). b
levels were noted, stressing the importance of optimisation of practice even if an automated dispensing system is used. On the other hand, values in centre B are showing importance of staff rotation. The collective dose per unit administered activity is 43 % lower in period II than in those period I. This means that after the optimisation of the work practice in centre B, staff members become more efficient as a team. The study has certain limitations. First, extremity dosimetry was available only in one centre. Secondly, contribution of different phases of radiopharmaceutical manipulation was not taken into account and in some cases, even contribution of other NM modalities. Thus, to further optimise PET/CT practice in these two centres, detailed measurements that can identify the phases where doses are high are indicated. CONCLUSION PET/CT requires special concern regarding occupational radiation protection. The level of whole-body and finger doses for technologists in the two PET/CT facilities in Serbia is presented. Although the individual doses are within the recommended regulatory limits, the increase in the workload would result in higher staff doses. Thus, an effort must be made to review the working procedure and reduce the radiation dose in both centres. The practice in both centres should be further investigated and appropriate protective measures subsequently be applied to reduce both whole-body and extremity doses as low as reasonably achievable.
FUNDING This work was supported by the Ministry of Education and Science of the Republic of Serbia (grant agreements: 43009, 171002 and 43002).
REFERENCES 1. Rohren, E. M., Turkington, T. G. and Coleman, E. Clinical applications of PET in oncology. Radiology 231, 305– 332 (2004). 2. Kumar, S., Pandey, A. K., Sharma, P., Shamim, S. A., Malhotra, A. and Kumar, R. Instantaneous exposure to nuclear medicine staff involved in PET-CT imaging in developing countries: experience from a tertiary care centre in India. Jpn J. Radiol. 30, 291– 295 (2012). 3. Dalianis, K., Malamitsia, J., Gogoua, L., Pagoua, M., Efthimiadoua, R., Andreoua, J., Louizı¨b, A. and Georgioub, E. Dosimetric evaluation of the staff working in a PET/CT department. Nucl. Instrum. Methods Phys. Res. A 569, 548– 550 (2006). 4. Demir, M., Demir, B., Yas¸ar, D., Sayman, H., Halac, ¨ zcan, K. and Uslu, I. Radiation doses M., Ahmed, A., O to technologists working with 18F-FDG in a PET center with high patient capacity. Nukleonika 55, 107–112 (2010). 5. Kopec, R., Budzanowski, M., Budzynska, A., Czepczynski, R., Dziuk, M., Sowinski, J. and Wyszomirska, A. On the relationship between whole body, extremity and eye lens doses for medical staff in the preparation and application of radiopharmaceuticals in nuclear medicine. Radiat. Meas. 46, 1295–1298 (2011).
Page 8 of 9
Downloaded from http://rpd.oxfordjournals.org/ at Northeastern University Libraries on March 31, 2014
— — — 5.9 6.5 4.6 8.9 3.1 17 4 –5 — 0.6–2.1 0.9–3.2 4.2–7 5 –6
Hp(10)/A (mSv GBq21)
OCCUPATIONAL RADIATION DOSE IN PET/CT 22. Wrzesie´n, M., Olszewski, J. and Jankowski, J. Hand exposure to ionising radiation of nuclear medicine workers. Radiat. Prot. Dosim. 130, 325– 330 (2008). 23. Madsen, M. T., Anderson, J. A., Halama, J. R., Kleck, J., Simpkin, D. J., Votaw, J. R., Wendt, R. E., Williams, L. E. and Yester, M. V. AAPM task group 108: PET and PET/CT shielding requirements. Med. Phys. 33(1), 4 –15 (2006). 24. The European Association of Nuclear Medicine. Best Practice in Nuclear Medicine, Part 1 A Technologist’s Guide. European Association of Nuclear Medicine (2006). 25. The European Association of Nuclear Medicine. Principles and Practice of PET/CT, Part 1: A Technologist’s Guide. European Association of Nuclear Medicine (2010). 26. International Atomic Energy Agency. Radiation Protection and Safety of Radiation Sources: International Basic Safety Standards, Interim Edition. International Atomic Energy Agency (2011). 27. Jankowski, J., Olszewski, J. and Kluska, K. Distribution of equivalent doses to skin of the hands of nuclear medicine personnel. Radiat. Prot. Dosim. 106, 177– 180 (2003). 28. International Atomic Energy Agency. Safety Reports Series No.40: applying radiation safety standards in nuclear medicine. IAEA (2005). 29. Antic, V., Stankovic´, K., Vujisic´, M. and Osmokrovic´, P. Comparison of various methods for designing the shielding from ionising radiation at PET-CT installations. Radiat. Prot. Dosim. 154, 245– 249 (2013). 30. Lineman, H., Will, E. and Beuthien-Baumann, B. Investigations of radiation exposure of the medical personnel during F-18-FDG PET studies. Nuklearmedizin 39, 77–81 (2000). 31. Zeff, B. W. and Yester, M. V. Patient self-attenuation and technologist dose in positron emission tomography. Med. Phys. 32, 861– 865 (2005). 32. Donadille, L., Carinou, E., Ginjaume, M., Jankowski, J., Rimpler, A., Sans Merce, M. and Vanhavere, F. An overview of the use of extremity dosemeters in some European countries for medical applications. Radiat. Prot. Dosim. 131, 62– 66 (2008). 33. Chiesa, C., De Sanctis, V., Crippa, F., Schiavini, M., Fraigola, C. E., Bogni, A., Pascali, C., Decise, D., Marchesini, R. and Bombardieri, E. Radiation dose to technicians per nuclear medicine procedure: comparison between technetium-99 m, gallium-67 and iodine-131. Eur. J. Nucl. Med. 24, 1380–1389 (1997). 34. Benatar, N. A., Cronin, B. F. and O’Doherty, M. J. Radiation dose rates from patients undergoing PET: implications for technologists and waiting areas. Eur. J. Nucl. Med. 27, 583 –589 (2000). 35. Pant, G. S. and Senthamizhchelvan, S. Radiation exposure to staff in a PET/CT facility. Indian J. Nucl. Med. 21, 100–103 (2006). 36. Peet, D. J., Morton, R., Hussein, M., Alsafi, K. and Spyrou, N. Radiation protection in fixed PET/CT facilities-design and operation. Br. J. Radiol. 85, 643– 646 (2012). 37. Covens, P., Berus, D., Vanhavere, F. and Caveliers, V. The introduction of automated dispensing and injection during PET procedures: a step in the optimisation of extremity doses and whole-body doses of nuclear medicine staff. Radiat. Prot. Dosim. 140, 250–258 (2010).
Page 9 of 9
Downloaded from http://rpd.oxfordjournals.org/ at Northeastern University Libraries on March 31, 2014
6. Guillet, B., Quentin, P., Waultier, S., Bourrelly, M., Pisano, P. and Mundler, O. Technologist radiation exposure in routine clinical practice with 18F-FDG PET. J. Nucl. Med. Technol. 33, 175– 179 (2005). 7. Leide-Svegborn, S. Radiation exposure of patients and personnel from a PET/CT procedure with 18F-FDG. Radiat. Prot. Dosim. 139, 208–213 (2010). 8. Cao, Z. J. et al. 18F protection issues: human and gcamera considerations. J. Nucl. Med. Technol. 31, 210 –215 (2003). 9. Seierstad, T., Stranden, E., Bjering, K., Evensen, M., Holt, A., Michalsen, H. M. and Wetteland, O. Doses to nuclear technicians in a dedicated PET/CT centre utilising 18F fluorodeoxyglucose (FDG). Radiat. Prot. Dosim. 123, 246– 249 (2007). 10. Vargas Castrilloon, S. and Cutanda Henriquez, F. A study on occupational exposure in a PET/CT facility. Radiat. Prot. Dosim. 147, 247–249 (2011). 11. Al-Haj, A. N., Lobriguito, A. M., Arafah, A. and Parker, R. Deriving staff and public doses in a PET/CT facility from measured radiation levels using thermoluminescent dosimetry. Radiat. Prot. Dosim. 144, 487 –491 (2011). 12. Demir, M., Demir, B., Sayman, H., Sager, S., Sabbir Ahmed, A. and Uslu, I. Radiation protection for accompanying person and radiation workers in PET/CT. Radiat. Prot. Dosim. 147, 528–532 (2011). 13. Sandouqa, A. S., Haddadin, I. M. and Abu-Khaled, Y. S. Hand equivalent doses of nuclear medicine staff in Jordan: preliminary experimental studies. Radiat. Meas. 46, 250–253 (2011). 14. Avila, O., Torres-Ulloaa, C. L., Medinac, L. A., Trujillo-Zamudioe, F. E., Gamboa-deBuenf, A. E., Buenfilc, A. E. and Brandanc, M. E. TL measurement of ambient dose at a Nuclear Medicine Department. Radiat. Meas. 46, 1843– 1846 (2011). 15. Carnicer, A. et al. The use of different types of thermoluminescent dosemeters to measure extremity doses in nuclear medicine. Radiat. Meas. 46, 1835–1838 (2011). 16. Sudbrock, F., Uhrhan, K., Rimpler, A. and Schicha, H. Dose and dose rate measurements for radiation exposure scenarios in nuclear medicine. Radiat. Meas. 46, 1303–1306 (2011). 17. Carnicer, A. et al. Hand exposure in diagnostic nuclear medicine with 18F- and 99mTc-labelled radiopharmaceuticals—results of the ORAMED project. Radiat. Meas. 46, 1277– 1282 (2011). 18. Roberts, F., Gunawardana, D. H., Pathmaraj, K., Wallace, A., U, P. L., Mi, T., Berlangieri, S. U., O’Keefe, G. J., Rowe, C. C. and Scott, A. M. Radiation dose to PET technologists and strategies to lower occupational exposure. J. Nucl. Med. Technol. 33, 44–47 (2005). 19. Quinn, B., Holahan, B., Aime, J., Humm, J., St Germain, J. and Dauer, L. T. Measured dose rate constant from oncology patients administered 18F for positron emission tomography. Med. Phys. 39(10), 6071–6079 (2012). 20. Chruscielewski, W., Olszewski, J., Jankowski, J. and Cygan, M. Hand exposure in nuclear medicine workers. Radiat. Prot. Dosim. 101, 229–232 (2002). 21. Vanhavere, F., Carinou, E., Donadille, L., Ginjaume, M., Jankowski, J., Rimpler, A. and Sans Merce, M. An overview of extremity dosimetry in medical applications. Radiat. Prot. Dosim. 129, 350–355 (2008).
