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Comparison of activity measurements in nuclear medicine ...

  1. 1. Alasbimn Journal Year 13, N°50, October 2010 / Año 13, Nº 50 , Octubre 2010 1Centro Regional de Ciências Nucleares do Nordeste Comissão Nacional de Energia Nuclear Av. Professor Luiz Freire, 200 50740-540, Recife/PE, Brasil 2Laboratório Nacional de Metrologia das Radiações Ionizantes Instituto de Radioproteção e Dosimetria Comissão Nacional de Energia Nuclear, Brasil Correspondencia: Cita / Reference: Fragoso, Maria da Conceição et al. Comparison of activity measurements in nuclear medicine services in Pernambuco.. Alasbimn Journal 13 (50): October 2010. Article N° AJ50-4. Summary Intercomparison is an important tool for quality assessment, because equipment performance and procedures are evaluated and compared. In nuclear medicine, this tool is wide utilized to evaluate the ability of the services to measure activities of radiopharmaceuticals which will be administered to the patients in diagnostic or therapeutic procedures. In this work, a comparison program of activity measurements of the 99mTc, 131I, 67Ga and 201Tl radionuclides was established in Pernambuco State, at the Brazilian Northeast, with the aim of evaluating the quality of routine measurements carried out in the NMS. The results in each NMS are sent to the Standard laboratory, which compares these results with the acceptance limits recommended by national regulations. All NMS participants complied with the limit established for the accuracy of measurement (±10%) and showed that their radionuclide calibrators are adequate for measurement of the activities of radiopharmaceuticals. Key words: Intercomparison, quality assurance, radionuclide calibrators. Resumo A intercomparação é uma importante ferramenta para avaliação da qualidade da medição da atividade de radiofármaco, porque não apenas o desempenho do equipamento é verificado, mas também todo procedimento de medição. Na medicina nuclear, esta ferramenta é amplamente utilizada para avaliar a habilidade dos serviços de medicina nuclear (SMN) na medição da atividade dos radiofármacos que serão administrados aos pacientes para diagnósticos ou procedimentos terapêuticos. Neste trabalho, Alasbimn Journal - Article AJ50-4 1 Comparison of activity measurements in nuclear medicine services in Pernambuco. Fragoso, Maria da Conceição1; Morais de Albuquerque, Antonio1; Paes Barreto, Flávio1; Iwahara, Akira2; De Andrade Lima, Ricardo1; Farias de Lima, Fabiana1; Oliveira, Mércia1.
  2. 2. Alasbimn Journal Year 13, N°50, October 2010 / Año 13, Nº 50 , Octubre 2010 um programa de intercomparação de medidas de atividades de radiofármacos, utilizando as fontes de99mTc,131I,67Ga e201Tl, foi estabelecido no estado de Pernambuco, região nordeste do Brasil, com o objetivo de avaliar a qualidade das medições realizadas nos SMN. Os resultados obtidos em cada SMN são enviados ao laboratório padrão, que os compara com os valores de referência recomendados pela norma nacional, verificando o desempenho destes instrumentos. Todos os SMN participantes respeitaram os limites estabelecidos para a exatidão das medidas (±10%), demonstrando que os calibradores de radionuclídeos estão adequados/apropriados para a medição de atividades de radiofármacos. Palabras clave: Intercomparação, controle de qualidade, calibradores de radionuclídeos. Introduction Radioactive materials are widely used for therapeutic or diagnostic medical purposes. As an example, there is the nuclear medicine. In this case, the determination of the activity managed to the patient plays an important role for the success of the therapy or the diagnostic procedure. Various regulations have been published worldwide limiting values for the maximum uncertainties permissible in activity measurements, as for an example the guide published in 2006 by the National Physical Laboratory, United Kingdom (NPL). The purpose of NPL is to present the quality controls tests that should be undertaken on a routine basis for medical radionuclide calibrators to ensure the accuracy and traceability of measurements of the activities of radiopharmaceuticals(1). In the same year, the National Henri Becquerel Laboratory (LNHB), in France, published a guide on utilization and quality control of radionuclide calibrators(2). In Brazil, these policies were established by the Brazilian Nuclear Energy Commission (CNEN) in the CNEN-NE-3.05 Standard(3). According to this standard, the correct value of the activity of a radiopharmaceutical should be known with the maximum uncertainty of ±10% before administration to the patient. The equipment utilized to measure the activity of radionuclides in Nuclear Medicine Services (NMS) is the radionuclide calibrator. This equipment consist of an ionization chamber (or a proportional counter) coupled to an electrometer. To guarantee the administration of the correct value of radiopharmaceutical activity to the patient, the appropriate use of the radionuclide calibrators is indispensable. This equipment is capable to carry through accurate activity measurements if adequate procedures are followed. Intercomparison programs are important tools for evaluation of the quality of the radiopharmaceutical activity measurements, because it can evaluate the equipment accuracy and the technical procedure or method employed(4,5). According to Santry D.(6)there are some aspects in a intercomparison program that should be pointed out: the establishment of this kind of program is simple because the NMS must follow its own procedure for the measurement of the radionuclide activity; the cost to implement this program is very low, because the NMS has all sources necessary to perform the comparisons; the measurement should be carried out at any time, in order to not disturb the NMS routine; unacceptable results can be quickly investigated; and all participants will have technical assistance of the standard laboratory in order to identify and correct eventual unacceptable results (Santry, 1998). Intercomparison of activity measurements started in 1973 at the USA(7). Nowadays, United Kingdom, Canada, Argentina, Hungry, Germany, India and Australia have intercomparison programs established (5). In all cases, it was observed an improvement of the quality of the activity measurements after the establishment of this program. Problems concerning equipments (instruments based on Geiger-Muller counters and/or decalibrated), manufacturer, procedures, and users were related in former works(5,8,9). Alasbimn Journal - Article AJ50-4 2
  3. 3. Alasbimn Journal Year 13, N°50, October 2010 / Año 13, Nº 50 , Octubre 2010 Since 1998, the National Laboratory for Ionizing Radiation Metrology (LMNRI) of the Radiation Protection and Dosimetry Institute (IRD) has been conducting intercomparison programs at Rio de Janeiro and surroundings(10,11). In the first round of comparisons, there were compared measurements of 131I and 99mTc. The results obtained were up to 41% higher than the reference value established by the LNMRI/IRD. The authors attribute these results due to the absent periodic calibration of the equipment and eventual failures at equipments and procedures(10). The second round of measurements showed an improvement of the quality of the measurement of activity in NMS at this city: the percentage of NMS in accordance to the acceptance criterion established by CNEN increased from 62.5% to 72.7% for the 131I activity measurements and from 78.3% to 86.4% for the 99mTc activity measurements(11). At present time, similar intercomparison programs are established at the South and Southeast Brazilian Regions(12). In a recent paper published by Tauhata et al(12)results of the surveys performed by LNMRI/IRD from 1999 up to 2006 are presented. In these surveys, only 42.9% of tested NMSs presented acceptable results in accordance to the acceptance criteria established. These results showed the necessity of the establishment of this program in whole Brazilian territory. The Northeastern Regional Centre for Nuclear Sciences (CRCN-NE/CNEN) was designated by the LNMRI to establish this program in the Brazilian Northeast. The aim of this work is to present the results of the establishment of the intercomparison program in Pernambuco, a State at the Brazilian Northeast. The results of131I,99mTc,67Ga and201Tl carried out between 2007 and 2008 are presented. Methods A radionuclide calibrator, Capintec, model CRC-15 was established as the standard instrument. There was established a quality control program at the laboratory, and precision, accuracy, reproducibility and linearity measurements have been done regularly, and the results have been analyzed following the CNEN recommendations(3). Following this standard, to assess the precision, the difference between the individual activities (Aι) and the mean value (Ã) was calculated using: while the accuracy was calculated using the equation: where à is the mean value of the measured activity and is the certified activity corrected for the radioactive decay to the day of measurement. To perform these tests, there were utilized the57Co,60Co,133Ba and137Cs standard sources. The linearity was evaluated using a99mTc source and accompanying its radioactive decay during 72 hours, by decaying source method. For each point, were made 10 consecutive measurements of activity and calculate the mean value. The measured values were plotted as a function of time and the experimental results was compared to the theoretical behavior. In addition, diary verification of voltage, auto zero and background radiation contribution have been performed. For the comparisons between CRCN and NMS, the99mTc,131I,67Ga and201Tl samples utilized were contained in glass vials with 5 ml of solution. The reference Alasbimn Journal - Article AJ50-4 3
  4. 4. Alasbimn Journal Year 13, N°50, October 2010 / Año 13, Nº 50 , Octubre 2010 value of activity was determined by measurements performed with the Capintec, CRC-15, radionuclide calibrator. The intercomparison program is divided in two steps: 1) The measurement at the nuclear medicine service (NMS) under evaluation: At the NMS, a technician, designed by the NMS manager, was asked to make three measurements for background radiation and five measurements of activity with the radionuclide sample; after, the three repeated measurements of background radiation are performed. A special questionnaire was written to standardize the measurements procedure; besides the results of the activity measurements, some information concerning the radionuclide calibrator itself (manufacturer, model, serial number, calibration date and operational voltage) are checked. 2) Measurement at CRCN: The same measurement procedure was repeated at CRCN with the same radionuclide sample measured at the NMS. The ratio was calculated for each measurement. According to the CNEN, the acceptable value for the accuracy on activity measurements for radionuclides utilized in Nuclear Medicine is ±10% (1). Results Performance of the standard radionuclide calibrator According to the CNEN-NE-3.05 Standard(3), the precision, the accuracy and the linearity tests must be performed twice a year, while the reproducibility test must be annual. However, in this work, the precision, the accuracy and the reproducibility tests were performed every day prior the utilization of the radionuclide calibrator. Only the linearity test was performed once a year. The data presented at Tables 1 and 2 and in Figure 1 correspond to the period from August, 2008 up to December, 2008. The results obtained for the whole period (2006-2008) are similar. Table 1 Results of the precision test performed at the standard radionuclide calibrator. Co-57 Ba-133 Cs-137 Co-60 Ai (μCi) AMean (μ Ci) Precisi on (%) Ai (μCi) AMean (μ Ci) Precisi on (%) Ai (μCi) AMean (μ Ci) Precisi on (%) Ai (μCi) AMean (μ Ci) Precisi on (%) 215 215 0,00 210 210 0,00 196 195 0,51 64 63,2 1,27 212 211,6 0,19 209 208,4 0,29 195 195 0,00 63 63 0,00 213 212,4 0,28 211 210,4 0,29 195 195 0,00 63 63 0,00 212 211,4 0,28 209 209 0,00 196 195,2 0,41 63 62,8 0,32 210 209,2 0,38 208 207,8 0,10 195 194,8 0,10 63 63 0,00 209 208,6 0,19 211 210,2 0,38 196 195,8 0,10 63 63 0,00 208 207 0,48 209 208,8 0,10 196 195,2 0,41 63 63 0,00 206 205,4 0,29 210 209,8 0,10 195 194,6 0,21 63 63 0,00 204 204 0,00 210 209,8 0,10 196 195,4 0,31 63 63 0,00 204 204 0,00 209 209 0,00 195 195 0,00 63 63 0,00 201 199,4 0,80 210 209,4 0,29 194 193,2 0,41 62 62 0,00 201 201 0,00 207 207 0,00 195 194,4 0,31 63 63 0 Table 2 Results of the accuracy test performed at the standard radionuclide calibrator. Co-57 Ba-133 Cs-137 Co-60 Ai (μCi) AMean (μ Ci) Precisio n (%) Ai (μCi) AMean (μ Ci) Precisio n (%) Ai (μCi) AMean (μ Ci) Precisio n (%) Ai (μCi) AMean (μ Ci) Precisio n (%) 211,6 215 -1,58 208,4 215 -3,07 195 188,7 3,34 63 62,3 1,12 212,4 215 -1,21 210,4 215 -2,14 195 188,7 3,34 63 62,2 1,29 211,4 214 -1,21 209 215 -2,79 195,2 188,7 3,44 62,8 62,2 0,96 209,2 212 -1,32 207,8 215 -3,35 194,8 188,6 3,29 63 62,1 1,45 208,6 211 -1,14 210,2 215 -2,23 195,8 188,6 3,82 63 62,1 1,45 207 210 -1,43 208,8 215 -2,88 195,2 188,6 3,50 63 62,1 1,45 205,4 208 -1,25 209,8 214 -1,96 194,6 188,5 3,24 63 62 1,61 204 207 -1,45 209,8 214 -1,96 195,4 188,5 3,66 63 61,9 1,78 204 207 -1,45 209 214 -2,34 195 188,5 3,45 63 61,9 1,78 199,4 204 -2,25 209,4 214 -2,15 193,2 188,4 2,55 62 61,8 0,32 201 204 -1,47 207 214 -3,27 194,4 188,4 3,18 63 61,8 1,94 197,2 201 -1,89 209 214 -2,34 194,6 188,4 3,29 62 61,7 0,49 Alasbimn Journal - Article AJ50-4 4
  5. 5. Alasbimn Journal Year 13, N°50, October 2010 / Año 13, Nº 50 , Octubre 2010 Figure 1. Results of the long term stability test to the standard radionuclide calibrator for the 57Co, 60Co, 133Ba and 137Cs standard sources. Due to the 57Co half-life, the results related to this source were corrected to the radioactive decay. All these results are in accordance to the Brazilian acceptance limits which are: 10% for the accuracy test, 5% for the precision test and 10% for the reproducibility test (CNEN, 1996). The linearity test was performed utilizing a 99mTc source with initial activity of 4.86 GBq. The results obtained were compared to the theoretical values, resulting in an error of 6%. These curves are showed in Figure 2 and demonstrate that the radionuclide calibrator presents a linear response for the range of activity used in the test. This result is in accordance to the Brazilian acceptance limits (±20%) (CNEN, 1996). Figure 2. Results of the linearity test. The squares represent the experimental data and the full line is the theoretical curve. Intercomparison results. Nine private and public NMS from Pernambuco participated in these two rounds of the intercomparison program. Each participant received an identifying code (A, B, C, D, E, F, G, H and I) in order to guarantee the anonymity. It was observed that all participants utilized Capintec radionuclide calibrator models based on ionization chambers, and all participants affirmed that they have a quality control program established in their routine measurements based on CNEN recommendations(3). However, only one performs diary tests as suggested by NPL(1). The same99mTc,131I,67Ga and201Tl samples were utilized to perform the measurements at the NMS and at CRCN. All measurements were corrected for decay to the time when the measurements at CRCN were executed. The results are showed in Figure 3. All NMS participants of these two rounds of comparisons complied with the limit established by CNEN for the accuracy of measurement (±10%) (CNEN, 1996) for the tested radionuclides.(3) Alasbimn Journal - Article AJ50-4 5
  6. 6. Alasbimn Journal Year 13, N°50, October 2010 / Año 13, Nº 50 , Octubre 2010 Figure 3. NMS/CRCN activity ratios for 99mTc, 131I, 67Ga and 201Tl sources in two years of the intercomparison program in Pernambuco. Conclusions The radionuclide calibrators chosen as the standard equipment in the intercomparison program presented an adequate performance compared to the Brazilian standard(3). The activity measurements intercomparison program was established in Recife, PE, as an important quality tool. Two rounds of comparisons were performed for99mTc and131I sources, while67Ga and201Tl sources were compared only once. In the first round, activity measurements of99mTc and131I were performed. All NMS participants demonstrated a very good capability to determine the activity of these two nuclides. Acknowledgements The authors are thankful to all participating institutions, to the LNMRI/IRD, and to the Centro de Radiofarmácia, Instituto de Pesquisas Energéticas e Nucleares, for providing the sources. The authors also acknowledge the financial support of the Fundação de Amparo à Ciência e Tecnologia do Estado de Pernambuco (FACEPE) and to the Comissão Nacional de Energia Nuclear (CNEN). Bibliography 1. Comissão Nacional de Energia Nuclear (CNEN). Requisitos de Radioproteção e Segurança para Serviços de Medicina Nuclear, CNEN-NN 3.05, 1996; Rio de Janeiro, Brasil. 2. Debertin K, Schrader H. Intercomparisons for quality assurance of activity measurements with radionuclide calibrators. Nucl Inst Meth Phys Res 1992;A312:241-5. 3. Furnari JC, De Cabrejas ML, Rotta MC, Iglicki FA, Milá MI, Magnavacca C, Dima JC, Rodríguez Pasqués RH. Impact of dose calibrators quality control programme in Argentina. Nucl Inst Meth Phys Res 1992;A312:269- 71. 4. Garfinkel SB, Hine GJ. Dose calibrator pilot study. NBS Technical Note 791, NBS, 1971;Washington, DC, 1-4. 5. Iwahara A, de Oliveira AE, Tauhata L, da Silva CJ, Lopes RT. Intercomparison of131I and99mTc activity measurements in Brazilian nuclear medicine services. Appl Radiat Isot 2001;54:489-96. 6. Iwahara A, de Oliveira AE, Tauhata L, da Silva CJ, Braghirolli AMS, Lopes RT. Performance of dose calibrators in Brazilian hospitals for activity measurements. Appl Radiat Isot 2002;56:361-7. 7. Laboratoire National Henri Becquerel (LNHB), 2006. Guide d’Utilisation et de Contrôle Qualité des Activimètres. NT LNHB 2006/033. 8. National Physical Laboratory (NPL), 2006. Protocol for Establishing and Maintaining the Calibration of Medical Radionuclide Calibrators and their Quality Control. No. 93, United Kingdom. 9. Oropesa P, Hernández AT, Serra R, Varela C. Comparisons of activity measurements with radionuclide calibrators – A tool for quality assessment and improvement in nuclear medicine. Appl Radiat Isot 2005;63:493-503. 10. Santry D. The Canadian experience in performing accuracy checks on administered doses of radiopharmaceuticals. Appl Radiat Isot 1998;49:1448- Alasbimn Journal - Article AJ50-4 6
  7. 7. Alasbimn Journal Year 13, N°50, October 2010 / Año 13, Nº 50 , Octubre 2010 53. 11. Szörényi Á, Vágvölgyi J, Zsinka A. Experiences of fifteen years on metrological supervision of radionuclide calibrators used in nuclear medicine. Appl Radiat Isot 1998;49:1459-61. 12. Tauhata L, Iwahara A, de Oliveira AE, Rezende EA, Delgado JU, da Silva CJ, ET AL. Proficiency tests in the determination of activity of radiopharmaceutical products measured by nuclear medicine services in 8 years of comparison programmes in Brazil. Appl Radiat Isot 2008;66:981-7. Alasbimn Journal - Article AJ50-4 7