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Recommendations to reduce hand exposure for standard nuclear medicine procedures
Radiation Measurements 46 (2011) 1330e1333
Contents lists available at ScienceDirect
Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
Recommendations to reduce hand exposure for standard nuclear medicine procedures M. Sans-Merce a, *, N. Ruiz a, I. Barth b, A. Carnicer c, L. Donadille d, P. Ferrari e, M. Fulop f, M. Ginjaume c, G. Gualdrini f, S. Krim g, F. Mariotti f, X. Ortega c, A. Rimpler b, F. Vanhavere g, S. Baechler a a
Institute of Radiation Physics, University Hospital Center (CHUV) and University of Lausanne, Rue du Grand-Pré 1, 1007 Lausanne, Switzerland Bundesamt für Strahlenschutz, Germany Universitat Politecnica de Catalunya (UPC), Spain d Institut de Radioprotection et de Sûreté Nucléaire (IRSN), France e Ente per le Nuove Tecnologie, l’Energia e l’Ambiente (ENEA), Italy f Slovak Medical University, Slovakia g Belgian Nuclear Research Centre (SCK$CEN), Belgium b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 7 March 2011 Received in revised form 7 July 2011 Accepted 10 July 2011
The optimization of the extremity dosimetry of medical staff in nuclear medicine was the aim of the Work Package 4 (WP4) of the ORAMED project, a Collaborative Project (2008e2011) supported by the European Commission within its 7th Framework Programme. Hand doses and dose distributions across the hands of medical staff working in nuclear medicine departments were evaluated through an extensive measurement program involving 32 hospitals in Europe and 139 monitored workers. The study included the most frequently used radionuclides, 99mTc- and 18F-labelled radiopharmaceuticals for diagnostic and 90Y-labelled ZevalinÒ and DOTATOC for therapy. Furthermore, Monte Carlo simulations were performed in different predefined scenarios to evaluate separately the efficacy of different radiation protection measures by comparing hand dose distributions according to various parameters. The present work gives recommendations based on results obtained with both measurements and simulations. This results in nine practical recommendations regarding the positioning of the dosemeters for an appropriate skin dose monitoring and the best protection means to reduce the personnel exposure. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: Skin dose Hand exposure Hand dose Hand monitoring Extremity dosimetry Nuclear medicine Recommendations
1. Introduction Nuclear medicine (NM) is associated to all uses of unsealed radioactive sources for diagnosis or therapy purposes. In NM, radiation protection of workers is a main concern (Vanhavere et al., 2008). In this field, high radionuclide activities are needed, from few tens to several thousands of MBq. Moreover, the procedures require the handling of radiopharmaceuticals at contact and/or very close to the hands and often pure beta-emitters and mixed photon/beta-emitters are used. Workers are often not aware of which part of the hand receives the highest dose. On the other hand, it is recommended to measure the skin dose at the location with presumably the highest exposure to comply with the dose limit for the hands of 500 mSv per year averaged over 1 cm2 (ICRP, 2007). Work package 4 of the ORAMED project (see www.oramed-
* Corresponding author. Tel.: þ41 22 3728068; fax: þ41 22 3726130. E-mail address: [email protected] (M. Sans-Merce). 1350-4487/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2011.07.011
fp7.eu), aimed at enlarging the general knowledge of hand doses delivered to NM staff when handling the most frequently used radiopharmaceuticals, i.e. those labelled with 99mTc and 18F for diagnostics, and those labelled with 90Y for therapy procedures. Based on this study, recommendations are proposed to reduce hand exposure to an acceptable level. 2. Material and methods The dose distribution across the hand was obtained by measuring Hp(0.07) at 11 points of each hand using appropriate thermoluminescent dosemeters (TLD) for beta and gamma radiation, previously attached on gloves or taped to the operator’s hands. 139 different nuclear medicine workers (90 workers exclusively performed diagnostic procedures, 43 exclusively performed therapy procedures and 6 workers were involved in both diagnostic and therapy procedures) across seven European countries participated in the measuring campaign using a unified protocol. The protocol included both phases: preparation and administration for
M. Sans-Merce et al. / Radiation Measurements 46 (2011) 1330e1333
diagnostic and therapeutic applications and all relevant information for radiation exposure (i.e. means of protection and tools) (Sans Merce et al., 2011). In addition, Monte Carlo simulations were carried out, using the MCNPX 2.5 code (Pelowitz, 2005), to study the influence of different parameters on the hand exposure, such as the effectiveness of different types of shielding, the positioning of the syringe or the vial in the hand and the volume of the source. The most commonly used shielding materials and thickness available in the 32 hospitals were chosen for the simulation study. Realistic scenarios involving voxelized hand phantoms were used for this purpose. The recommendations were elaborated by considering the results of the statistical analysis of measurements for both diagnostic (Carnicer et al., 2011) and therapeutic (Rimpler et al., 2011) procedures, and those derived from the simulation studies (Ferrari et al., 2011).
3. Results The analysis of the large number of collected data together with validated Monte Carlo simulations led to the here stated observations. Local skin doses in nuclear medicine are high and can easily exceed the annual skin equivalent dose limit of 500 mSv. The annual skin equivalent dose of the monitored workers involved in diagnostic procedures for the ORAMED project has been estimated. For this estimation, only those procedures from which ORAMED measured values were available, for a specific worker, have been considered. Their workload and the activity manipulated per year for each radionuclide, was considered. The estimated annual dose is below 150 mSv, i.e. 3/10 of the annual limit, for 49% of the workers; between 150 mSv and 500 mSv for 31% of them and for 20% of the workers the annual dose limit was exceeded. Other authors had already reported cases where workers surpassed the annual dose limit (Chruscielewski et al., 2002; Wrzesién et al., 2008). The dose distribution over the hand depends on several factors. Firstly, the physical properties of the manipulated radionuclides have to be considered. Secondly, as expected, the distance between the source and the hand plays an important role; those dosemeters placed further from the source are less exposed. Moreover, a key factor is the use of shields. Adequate shields reduce significantly the exposure to those parts of the hands covered by the shield, as also demonstrated by other studies (Smart, 2004; Whitby and Martin, 2005). Adapted shields should be used whenever it is possible, as it is proposed in ICRP Publication 106 (ICRP, 2008). Nevertheless, even when performing the same procedure with the same devices the exposure vary significantly from one worker to another due to the worker’s individual habits. For each worker, the maximum dose to the hands normalized by the manipulated activity was determined. For a given procedure, mean, median, maximum and minimum values were calculated from those maximum dose values
Table 1 Mean, median, maximum and minimum values of the maximum doses to the hands, normalized to the manipulated activity, for all workers (excluding outliers) and procedures (P stands for preparation and A for administration).
of each worker. All these values are given in Table 1. A large spread of doses is observed for the same procedure, as shown in Table 1. It can also be concluded from Table 1, that usually preparation delivers higher doses than administration. Moreover, dose values for diagnostics remain much lower than those measured for therapeutic procedures. Concerning the positioning of the dosemeters for an adequate monitoring, some general trends have been observed among monitored workers. First, doses to the non-dominant hand are usually higher than doses to the dominant hand. Moreover, the tip of the index finger is generally the most exposed position on the hand; however, it is not a comfortable position for routine monitoring. For diagnostic procedures the skin dose, at the 22 monitored hand positions, was found to be correlated to the maximum dose (r > 0.6, p < 0.05). The highest correlation (r > 0.8, p < 0.05) was found for the tips of the fingers, especially those of the nondominant hand. For therapy procedures, the highest correlation was found for the tip of the index finger of the non-dominant hand (r > 0.7, p < 0.01). The impact of placing the routine dosemeter at a different position than that corresponding to the maximum skin dose has been estimated by calculating correction factors. Those factors are the ratios between the maximum dose in the hands and the dose measured at the most common positions for routine monitoring, i.e. the base of the index or the ring finger. There is a large spread on the values obtained for the correction factors as shown in Table 2. Excluding the data for the index tip, not a very comfortable position for routine monitoring, the correction factors for the base of the index finger of the non-dominant hand are lower and have smaller variability than the factors for the other monitoring positions. Concerning the parameters influencing the hand dose, some general trends have been observed among the monitored workers for all procedures. First, the extremely wide range of maximum doses measured for an identical procedure indicates that good and bad practices were performed and thus those workers who were found to be more exposed could potentially optimize their working procedures or habits. The largest exposures were found when working without shielded syringe and/or vial, and when having direct contact with the source container. In addition, several cases of contamination were also identified during measurements. Some workers associated with very low exposure used advanced techniques, including semi-automatic dispensing tools. Doses when working without vial or syringe shields are statistically higher for all studied procedures (p < 0.039 and p < 0.016, respectively). Only procedures where enough data was available could be considered in the statistical analysis. The shielding thickness and material has to be adapted to the radionuclide and geometry. Through the Monte Carlo simulations, the minimum thickness of shielding and the different shielding materials have been defined. It was found that the worker’s experience level was not decisive in reducing hand exposure. On the other hand, training on good practice (e.g. procedure planning, repeating procedures using non radioactive sources) and using appropriate radiation protection measures (e.g. shielding, forceps) were key elements to reduce exposures to an acceptable level, in good agreement with ICRP Publication 106 recommendations (ICRP, 2008). 4. Recommendations
Maximum doses from all workers (mSv/GBq)
P e 99mTc A e 99mTc P e 18F A e 18F P e 90Y Zevalin A e 90Y Zevalin
1331
Mean
Median
Minimum
Maximum
0.43 0.23 1.20 0.93 11.0 4.8
0.25 0.12 0.83 0.64 9.5 2.9
0.03 0.01 0.10 0.14 1.2 1.0
2.06 0.95 4.43 4.11 43.9 11.9
The following recommendations were derived from the observations and results of the WP4 of the ORAMED project: ➢ Hand monitoring is essential in nuclear medicine. ➢ To determine the position for routine monitoring, the most exposed position on the hand for each worker should be
1332
M. Sans-Merce et al. / Radiation Measurements 46 (2011) 1330e1333
Table 2 Range, median and mean values for the correction factors for the different positions in the hand and for each procedure (P stands for preparation and A for administration). Correction factors are evaluated by considering the ratios between Hp,max, the maximum of the mean Hp(0.07) (mSv/GBq) when both hands are considered simultaneously, and Hp,base ring, Hp,wrist, Hp,base index and Hp,index tip the mean dose at the base of the ring finger, the wrist, the base of the index and the tip of the index, respectively, for the nondominant and dominant hand. Non dominant hand
Pe
99m
Ae
99m
Pe
18
Ae
18
Pe
90
Ae
90
Tc
F
F
Y
Y
Tc
Range Median Mean Range Median Mean Range Median Mean Range Median Mean Range Median Mean Range Median Mean
Dominant hand
Max/Wrist
Max/base index
Max/base ring
Max/index tip
Max/wrist
Max/base index
Max/base ring
Max/index tip
3e55 17 21 6e93 17 26 3e30 12 15 5e68 18 21 3e42 12 15 5102 21 27
2e16 4 5 2e38 6 9 2e12 3 4 2e24 4 5 2e18 6 6 318 7 7
2e44 7 8 3e60 10 15 2e22 5 6 2e34 6 9 2e51 11 12 1e89 13 19
1e5 1 2 1e12 2 3 1e9 2 2 1e4 2 2 1e17 2 4 1e7 1 3
4e55 14 19 2e93 16 23 3e46 10 12 4e46 15 19 3e32 14 15 2e46 17 26
2e18 4 6 2e13 7 8 2e8 4 5 1e26 4 6 2e79 15 24 3e60 12 21
3e25 6 8 4e49 12 13 1e23 5 7 3e28 9 10 4e85 22 34 2e90 15 27
1e11 2 3 1e9 3 4 1e5 2 2 1e12 2 3 1e75 5 16 1e25 5 10
found by individual measurements for a short trial period. If for practical reasons, these measurements are not possible, the base of the index finger of the non-dominant hand with the sensitive part of the dosemeter placed towards the inside of the hand is the recommended position for routine hand monitoring in nuclear medicine. ➢ To estimate the maximum dose, the reading of the dosemeter worn at the base of the index finger of the non-dominant hand should be multiplied by a factor of 6. ➢ Shielding of vials and syringes is essential. This is a precondition but not a guarantee for low exposure, since sometimes shielding is not properly used.
➢ The minimum acceptable thickness of shielding for a syringe is 2 mm of tungsten for 99mTc and 5 mm of tungsten for 18F. For 90Y, 10 mm of PMMA completely shields beta radiation, but a shielding of 5 mm of tungsten provides better protection, as it cuts down bremsstrahlung radiation. ➢ The minimum acceptable shielding required for a vial is 3 mm of lead for 99mTc and 3 cm of lead for 18F. For 90Y, acceptable shielding is obtained with 10 mm of PMMA with an external layer of a few mm of lead. ➢ Any tool increasing the distance (e.g. forceps, automatic injector) between the hands/fingers and the source is very effective for dose reduction.
Fig. 1. Dose estimation tool.
M. Sans-Merce et al. / Radiation Measurements 46 (2011) 1330e1333
➢ Training and education in good practices (e.g. procedure planning, repeating procedures using non radioactive sources, estimation of doses to be received) are more relevant parameters than the worker’s experience level. ➢ Working fast is not sufficient, the use of shields or increasing the distance are more effective than working quickly. Concerning the estimation of exposures to be received, a dose estimation tool has been developed based on the ORAMED results and it is available via the ORAMED website. This dose estimation tool provides values for the expected doses at 11 different points in each hand when preparing or injecting one the radionuclides studied within the ORAMED project (99mTc, 18F or 90Y ZevalinÒ), as shown in Fig. 1. The ORAMED recommendations agree with most of the ICRP (ICRP, 2008) recommendations for nuclear medicine. Two main differences have been found concerning the routine monitoring. ICRP recommends placing the routine dosemeter on the base of the middle finger with the detector positioned on the palm side when the tip can’t be used, whereas ORAMED results show that the base of the index finger is a more appropriate position. A second difference is related to the correction factor proposed to estimate the maximum dose. ICRP recommends to apply a correction factor of 3 (6 if the dosemeter faces the back) whereas ORAMED results suggest a factor of 6. 5. Conclusions A series of measurements and Monte Carlo simulations were performed to optimize the extremity dosimetry of medical staff in nuclear medicine. Despite the fact of the wide range of doses measured for different workers and the multiple parameters that influence hand exposure, some general trends were found among the results leading to nine recommendations. These recommendations are compiled on a three page leaflet available on the ORAMED website.
1333
Acknowledgement The research leading to these results has received funding from the European Atomic Energy Community’s Seventh Framework Programme (FP7/2007e2011) under grant agreement n 211361. References Carnicer, A., Sans-Merce, M., Baechler, S., Barth, I., Donadille, L., Ferrari, P., Fulop, M., Ginjaume, M., Gualdrini, G., Krim, S., Mariotti, F., Ortega, X., Rimpler, A., Ruiz, N., Vanhavere, F., 2011. Hand exposure in diagnostic nuclear medicine with 18Fand 99mTc-labelled radiopharmaceuticals - Results of the ORAMED project. Radiat. Meas. 46 (11), 1277e1282. Chruscielewski, W., Olszewski, J., Jankowski, J., Cygan, M., 2002. Hand exposure in nuclear medicine workers. Radiat. Prot. Dosim. 101 (1e4), 229e232. Ferrari, P., Sans-Merce, M., Carnicer, A., Donadille, L., Fulop, M., Ginjaume, M., Gualdrini, G., Mariotti, F., Ruiz, N., 2011. Main results of the Monte Carlo studies carried out for nuclear medicine practices within the ORAMED project. Radiat. Meas. 46 (11), 1287e1290. ICRP, 2007. International Commission on Radiological Protection. The 2007 Recommendations of the International Commission on Radiological Protection, 103. ICRP Publication. Ann. ICRP 37(2e4). ICRP, 2008. Radiation Dose to Patients from Radiopharmaceuticals - Addendum 3 to ICRP Publication 53, 106. ICRP Publication. Ann. ICRP 38 (1e2), Annex E. Pelowitz, D.B., 2005. MCNPX User’s Manual. LA-CP-05e0369. Los Alamos Laboratoty, USA. Rimpler, A., Barth, I., Ferrari, P., Baechler, S., Carnicer, A., Donadille, L., Fulop, M., Ginjaume, M., Mariotti, M., Sans-Merce, M., Gualdrini, G., Krim, S., Ortega, X., Ruiz, N., Vanhavere, F., 2011. Extremity exposure in nuclear medicine therapy with 90Y-labelled substances - Results of the ORAMED project. Radiat. Meas. 46 (11), 1283e1286. Sans-Merce, M., Ruiz, N., Barth, I., Carnicer, A., Donadille, L., Ferrari, P., Fulop, M., Ginjaume, M., Gualdrini, G., Krim, S., Mariotti, F., Ortega, X., Rimpler, A., Vanhavere, F., Baechler, S., 2011. Extremity exposure in nuclear medicine: preliminary results of a European study. Radiat. Prot. Dosim. 144 (1e4), 515e520. Smart, R., 2004. Task-specific monitoring of nuclear medicine technologists’ radiation exposure. Radiat. Prot. Dosim. 109 (3), 201e209. Vanhavere, F., Carinou, E., Donadille, L., Ginjaume, M., Jankowski, J., Rimpler, A., Sans Merce, M., 2008. An overview on extremity dosimetry in medical applications. Radiat. Prot. Dosim. 129, 350e355. Whitby, M., Martin, C.J., 2005. A multi-centre study of dispensing methods and hand doses in UK hospital radiopharmacies. Nucl. Med. Commun. 26, 49e60. Wrzesién, M., Olszewski, J., Jankowski, J., 2008. Hand exposure to ionising radiation of nuclear medicine workers. Radiat. Prot. Dosim. 130 (3), 325e330.
Contents lists available at ScienceDirect
Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
Recommendations to reduce hand exposure for standard nuclear medicine procedures M. Sans-Merce a, *, N. Ruiz a, I. Barth b, A. Carnicer c, L. Donadille d, P. Ferrari e, M. Fulop f, M. Ginjaume c, G. Gualdrini f, S. Krim g, F. Mariotti f, X. Ortega c, A. Rimpler b, F. Vanhavere g, S. Baechler a a
Institute of Radiation Physics, University Hospital Center (CHUV) and University of Lausanne, Rue du Grand-Pré 1, 1007 Lausanne, Switzerland Bundesamt für Strahlenschutz, Germany Universitat Politecnica de Catalunya (UPC), Spain d Institut de Radioprotection et de Sûreté Nucléaire (IRSN), France e Ente per le Nuove Tecnologie, l’Energia e l’Ambiente (ENEA), Italy f Slovak Medical University, Slovakia g Belgian Nuclear Research Centre (SCK$CEN), Belgium b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 7 March 2011 Received in revised form 7 July 2011 Accepted 10 July 2011
The optimization of the extremity dosimetry of medical staff in nuclear medicine was the aim of the Work Package 4 (WP4) of the ORAMED project, a Collaborative Project (2008e2011) supported by the European Commission within its 7th Framework Programme. Hand doses and dose distributions across the hands of medical staff working in nuclear medicine departments were evaluated through an extensive measurement program involving 32 hospitals in Europe and 139 monitored workers. The study included the most frequently used radionuclides, 99mTc- and 18F-labelled radiopharmaceuticals for diagnostic and 90Y-labelled ZevalinÒ and DOTATOC for therapy. Furthermore, Monte Carlo simulations were performed in different predefined scenarios to evaluate separately the efficacy of different radiation protection measures by comparing hand dose distributions according to various parameters. The present work gives recommendations based on results obtained with both measurements and simulations. This results in nine practical recommendations regarding the positioning of the dosemeters for an appropriate skin dose monitoring and the best protection means to reduce the personnel exposure. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: Skin dose Hand exposure Hand dose Hand monitoring Extremity dosimetry Nuclear medicine Recommendations
1. Introduction Nuclear medicine (NM) is associated to all uses of unsealed radioactive sources for diagnosis or therapy purposes. In NM, radiation protection of workers is a main concern (Vanhavere et al., 2008). In this field, high radionuclide activities are needed, from few tens to several thousands of MBq. Moreover, the procedures require the handling of radiopharmaceuticals at contact and/or very close to the hands and often pure beta-emitters and mixed photon/beta-emitters are used. Workers are often not aware of which part of the hand receives the highest dose. On the other hand, it is recommended to measure the skin dose at the location with presumably the highest exposure to comply with the dose limit for the hands of 500 mSv per year averaged over 1 cm2 (ICRP, 2007). Work package 4 of the ORAMED project (see www.oramed-
* Corresponding author. Tel.: þ41 22 3728068; fax: þ41 22 3726130. E-mail address: [email protected] (M. Sans-Merce). 1350-4487/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2011.07.011
fp7.eu), aimed at enlarging the general knowledge of hand doses delivered to NM staff when handling the most frequently used radiopharmaceuticals, i.e. those labelled with 99mTc and 18F for diagnostics, and those labelled with 90Y for therapy procedures. Based on this study, recommendations are proposed to reduce hand exposure to an acceptable level. 2. Material and methods The dose distribution across the hand was obtained by measuring Hp(0.07) at 11 points of each hand using appropriate thermoluminescent dosemeters (TLD) for beta and gamma radiation, previously attached on gloves or taped to the operator’s hands. 139 different nuclear medicine workers (90 workers exclusively performed diagnostic procedures, 43 exclusively performed therapy procedures and 6 workers were involved in both diagnostic and therapy procedures) across seven European countries participated in the measuring campaign using a unified protocol. The protocol included both phases: preparation and administration for
M. Sans-Merce et al. / Radiation Measurements 46 (2011) 1330e1333
diagnostic and therapeutic applications and all relevant information for radiation exposure (i.e. means of protection and tools) (Sans Merce et al., 2011). In addition, Monte Carlo simulations were carried out, using the MCNPX 2.5 code (Pelowitz, 2005), to study the influence of different parameters on the hand exposure, such as the effectiveness of different types of shielding, the positioning of the syringe or the vial in the hand and the volume of the source. The most commonly used shielding materials and thickness available in the 32 hospitals were chosen for the simulation study. Realistic scenarios involving voxelized hand phantoms were used for this purpose. The recommendations were elaborated by considering the results of the statistical analysis of measurements for both diagnostic (Carnicer et al., 2011) and therapeutic (Rimpler et al., 2011) procedures, and those derived from the simulation studies (Ferrari et al., 2011).
3. Results The analysis of the large number of collected data together with validated Monte Carlo simulations led to the here stated observations. Local skin doses in nuclear medicine are high and can easily exceed the annual skin equivalent dose limit of 500 mSv. The annual skin equivalent dose of the monitored workers involved in diagnostic procedures for the ORAMED project has been estimated. For this estimation, only those procedures from which ORAMED measured values were available, for a specific worker, have been considered. Their workload and the activity manipulated per year for each radionuclide, was considered. The estimated annual dose is below 150 mSv, i.e. 3/10 of the annual limit, for 49% of the workers; between 150 mSv and 500 mSv for 31% of them and for 20% of the workers the annual dose limit was exceeded. Other authors had already reported cases where workers surpassed the annual dose limit (Chruscielewski et al., 2002; Wrzesién et al., 2008). The dose distribution over the hand depends on several factors. Firstly, the physical properties of the manipulated radionuclides have to be considered. Secondly, as expected, the distance between the source and the hand plays an important role; those dosemeters placed further from the source are less exposed. Moreover, a key factor is the use of shields. Adequate shields reduce significantly the exposure to those parts of the hands covered by the shield, as also demonstrated by other studies (Smart, 2004; Whitby and Martin, 2005). Adapted shields should be used whenever it is possible, as it is proposed in ICRP Publication 106 (ICRP, 2008). Nevertheless, even when performing the same procedure with the same devices the exposure vary significantly from one worker to another due to the worker’s individual habits. For each worker, the maximum dose to the hands normalized by the manipulated activity was determined. For a given procedure, mean, median, maximum and minimum values were calculated from those maximum dose values
Table 1 Mean, median, maximum and minimum values of the maximum doses to the hands, normalized to the manipulated activity, for all workers (excluding outliers) and procedures (P stands for preparation and A for administration).
of each worker. All these values are given in Table 1. A large spread of doses is observed for the same procedure, as shown in Table 1. It can also be concluded from Table 1, that usually preparation delivers higher doses than administration. Moreover, dose values for diagnostics remain much lower than those measured for therapeutic procedures. Concerning the positioning of the dosemeters for an adequate monitoring, some general trends have been observed among monitored workers. First, doses to the non-dominant hand are usually higher than doses to the dominant hand. Moreover, the tip of the index finger is generally the most exposed position on the hand; however, it is not a comfortable position for routine monitoring. For diagnostic procedures the skin dose, at the 22 monitored hand positions, was found to be correlated to the maximum dose (r > 0.6, p < 0.05). The highest correlation (r > 0.8, p < 0.05) was found for the tips of the fingers, especially those of the nondominant hand. For therapy procedures, the highest correlation was found for the tip of the index finger of the non-dominant hand (r > 0.7, p < 0.01). The impact of placing the routine dosemeter at a different position than that corresponding to the maximum skin dose has been estimated by calculating correction factors. Those factors are the ratios between the maximum dose in the hands and the dose measured at the most common positions for routine monitoring, i.e. the base of the index or the ring finger. There is a large spread on the values obtained for the correction factors as shown in Table 2. Excluding the data for the index tip, not a very comfortable position for routine monitoring, the correction factors for the base of the index finger of the non-dominant hand are lower and have smaller variability than the factors for the other monitoring positions. Concerning the parameters influencing the hand dose, some general trends have been observed among the monitored workers for all procedures. First, the extremely wide range of maximum doses measured for an identical procedure indicates that good and bad practices were performed and thus those workers who were found to be more exposed could potentially optimize their working procedures or habits. The largest exposures were found when working without shielded syringe and/or vial, and when having direct contact with the source container. In addition, several cases of contamination were also identified during measurements. Some workers associated with very low exposure used advanced techniques, including semi-automatic dispensing tools. Doses when working without vial or syringe shields are statistically higher for all studied procedures (p < 0.039 and p < 0.016, respectively). Only procedures where enough data was available could be considered in the statistical analysis. The shielding thickness and material has to be adapted to the radionuclide and geometry. Through the Monte Carlo simulations, the minimum thickness of shielding and the different shielding materials have been defined. It was found that the worker’s experience level was not decisive in reducing hand exposure. On the other hand, training on good practice (e.g. procedure planning, repeating procedures using non radioactive sources) and using appropriate radiation protection measures (e.g. shielding, forceps) were key elements to reduce exposures to an acceptable level, in good agreement with ICRP Publication 106 recommendations (ICRP, 2008). 4. Recommendations
Maximum doses from all workers (mSv/GBq)
P e 99mTc A e 99mTc P e 18F A e 18F P e 90Y Zevalin A e 90Y Zevalin
1331
Mean
Median
Minimum
Maximum
0.43 0.23 1.20 0.93 11.0 4.8
0.25 0.12 0.83 0.64 9.5 2.9
0.03 0.01 0.10 0.14 1.2 1.0
2.06 0.95 4.43 4.11 43.9 11.9
The following recommendations were derived from the observations and results of the WP4 of the ORAMED project: ➢ Hand monitoring is essential in nuclear medicine. ➢ To determine the position for routine monitoring, the most exposed position on the hand for each worker should be
1332
M. Sans-Merce et al. / Radiation Measurements 46 (2011) 1330e1333
Table 2 Range, median and mean values for the correction factors for the different positions in the hand and for each procedure (P stands for preparation and A for administration). Correction factors are evaluated by considering the ratios between Hp,max, the maximum of the mean Hp(0.07) (mSv/GBq) when both hands are considered simultaneously, and Hp,base ring, Hp,wrist, Hp,base index and Hp,index tip the mean dose at the base of the ring finger, the wrist, the base of the index and the tip of the index, respectively, for the nondominant and dominant hand. Non dominant hand
Pe
99m
Ae
99m
Pe
18
Ae
18
Pe
90
Ae
90
Tc
F
F
Y
Y
Tc
Range Median Mean Range Median Mean Range Median Mean Range Median Mean Range Median Mean Range Median Mean
Dominant hand
Max/Wrist
Max/base index
Max/base ring
Max/index tip
Max/wrist
Max/base index
Max/base ring
Max/index tip
3e55 17 21 6e93 17 26 3e30 12 15 5e68 18 21 3e42 12 15 5102 21 27
2e16 4 5 2e38 6 9 2e12 3 4 2e24 4 5 2e18 6 6 318 7 7
2e44 7 8 3e60 10 15 2e22 5 6 2e34 6 9 2e51 11 12 1e89 13 19
1e5 1 2 1e12 2 3 1e9 2 2 1e4 2 2 1e17 2 4 1e7 1 3
4e55 14 19 2e93 16 23 3e46 10 12 4e46 15 19 3e32 14 15 2e46 17 26
2e18 4 6 2e13 7 8 2e8 4 5 1e26 4 6 2e79 15 24 3e60 12 21
3e25 6 8 4e49 12 13 1e23 5 7 3e28 9 10 4e85 22 34 2e90 15 27
1e11 2 3 1e9 3 4 1e5 2 2 1e12 2 3 1e75 5 16 1e25 5 10
found by individual measurements for a short trial period. If for practical reasons, these measurements are not possible, the base of the index finger of the non-dominant hand with the sensitive part of the dosemeter placed towards the inside of the hand is the recommended position for routine hand monitoring in nuclear medicine. ➢ To estimate the maximum dose, the reading of the dosemeter worn at the base of the index finger of the non-dominant hand should be multiplied by a factor of 6. ➢ Shielding of vials and syringes is essential. This is a precondition but not a guarantee for low exposure, since sometimes shielding is not properly used.
➢ The minimum acceptable thickness of shielding for a syringe is 2 mm of tungsten for 99mTc and 5 mm of tungsten for 18F. For 90Y, 10 mm of PMMA completely shields beta radiation, but a shielding of 5 mm of tungsten provides better protection, as it cuts down bremsstrahlung radiation. ➢ The minimum acceptable shielding required for a vial is 3 mm of lead for 99mTc and 3 cm of lead for 18F. For 90Y, acceptable shielding is obtained with 10 mm of PMMA with an external layer of a few mm of lead. ➢ Any tool increasing the distance (e.g. forceps, automatic injector) between the hands/fingers and the source is very effective for dose reduction.
Fig. 1. Dose estimation tool.
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➢ Training and education in good practices (e.g. procedure planning, repeating procedures using non radioactive sources, estimation of doses to be received) are more relevant parameters than the worker’s experience level. ➢ Working fast is not sufficient, the use of shields or increasing the distance are more effective than working quickly. Concerning the estimation of exposures to be received, a dose estimation tool has been developed based on the ORAMED results and it is available via the ORAMED website. This dose estimation tool provides values for the expected doses at 11 different points in each hand when preparing or injecting one the radionuclides studied within the ORAMED project (99mTc, 18F or 90Y ZevalinÒ), as shown in Fig. 1. The ORAMED recommendations agree with most of the ICRP (ICRP, 2008) recommendations for nuclear medicine. Two main differences have been found concerning the routine monitoring. ICRP recommends placing the routine dosemeter on the base of the middle finger with the detector positioned on the palm side when the tip can’t be used, whereas ORAMED results show that the base of the index finger is a more appropriate position. A second difference is related to the correction factor proposed to estimate the maximum dose. ICRP recommends to apply a correction factor of 3 (6 if the dosemeter faces the back) whereas ORAMED results suggest a factor of 6. 5. Conclusions A series of measurements and Monte Carlo simulations were performed to optimize the extremity dosimetry of medical staff in nuclear medicine. Despite the fact of the wide range of doses measured for different workers and the multiple parameters that influence hand exposure, some general trends were found among the results leading to nine recommendations. These recommendations are compiled on a three page leaflet available on the ORAMED website.
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Acknowledgement The research leading to these results has received funding from the European Atomic Energy Community’s Seventh Framework Programme (FP7/2007e2011) under grant agreement n 211361. References Carnicer, A., Sans-Merce, M., Baechler, S., Barth, I., Donadille, L., Ferrari, P., Fulop, M., Ginjaume, M., Gualdrini, G., Krim, S., Mariotti, F., Ortega, X., Rimpler, A., Ruiz, N., Vanhavere, F., 2011. Hand exposure in diagnostic nuclear medicine with 18Fand 99mTc-labelled radiopharmaceuticals - Results of the ORAMED project. Radiat. Meas. 46 (11), 1277e1282. Chruscielewski, W., Olszewski, J., Jankowski, J., Cygan, M., 2002. Hand exposure in nuclear medicine workers. Radiat. Prot. Dosim. 101 (1e4), 229e232. Ferrari, P., Sans-Merce, M., Carnicer, A., Donadille, L., Fulop, M., Ginjaume, M., Gualdrini, G., Mariotti, F., Ruiz, N., 2011. Main results of the Monte Carlo studies carried out for nuclear medicine practices within the ORAMED project. Radiat. Meas. 46 (11), 1287e1290. ICRP, 2007. International Commission on Radiological Protection. The 2007 Recommendations of the International Commission on Radiological Protection, 103. ICRP Publication. Ann. ICRP 37(2e4). ICRP, 2008. Radiation Dose to Patients from Radiopharmaceuticals - Addendum 3 to ICRP Publication 53, 106. ICRP Publication. Ann. ICRP 38 (1e2), Annex E. Pelowitz, D.B., 2005. MCNPX User’s Manual. LA-CP-05e0369. Los Alamos Laboratoty, USA. Rimpler, A., Barth, I., Ferrari, P., Baechler, S., Carnicer, A., Donadille, L., Fulop, M., Ginjaume, M., Mariotti, M., Sans-Merce, M., Gualdrini, G., Krim, S., Ortega, X., Ruiz, N., Vanhavere, F., 2011. Extremity exposure in nuclear medicine therapy with 90Y-labelled substances - Results of the ORAMED project. Radiat. Meas. 46 (11), 1283e1286. Sans-Merce, M., Ruiz, N., Barth, I., Carnicer, A., Donadille, L., Ferrari, P., Fulop, M., Ginjaume, M., Gualdrini, G., Krim, S., Mariotti, F., Ortega, X., Rimpler, A., Vanhavere, F., Baechler, S., 2011. Extremity exposure in nuclear medicine: preliminary results of a European study. Radiat. Prot. Dosim. 144 (1e4), 515e520. Smart, R., 2004. Task-specific monitoring of nuclear medicine technologists’ radiation exposure. Radiat. Prot. Dosim. 109 (3), 201e209. Vanhavere, F., Carinou, E., Donadille, L., Ginjaume, M., Jankowski, J., Rimpler, A., Sans Merce, M., 2008. An overview on extremity dosimetry in medical applications. Radiat. Prot. Dosim. 129, 350e355. Whitby, M., Martin, C.J., 2005. A multi-centre study of dispensing methods and hand doses in UK hospital radiopharmacies. Nucl. Med. Commun. 26, 49e60. Wrzesién, M., Olszewski, J., Jankowski, J., 2008. Hand exposure to ionising radiation of nuclear medicine workers. Radiat. Prot. Dosim. 130 (3), 325e330.