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Characterization of a medical X-ray machine for testing the response of electronic dosimeters in pulsed radiation fields
Radiation Physics and Chemistry ∎ (∎∎∎∎) ∎∎∎–∎∎∎
Contents lists available at ScienceDirect
Radiation Physics and Chemistry journal homepage: www.elsevier.com/locate/radphyschem
Characterization of a medical X-ray machine for testing the response of electronic dosimeters in pulsed radiation fields Margarete C. Guimarães a, Teógenes A. Da Silva a,b,n a b
Postgraduation Course of Science and Technology of Radiations, Minerals and Materials, CDTN/CNEN, Belo Horizonte, Brazil Development Center of Nuclear Technology, CDTN/CNEN, Belo Horizonte, Brazil
H I G H L I G H T S
Electronic personal dosimeters (EPD) have been used for personnel monitoring. EPD use has been extended to pulsed radiation beams. Deficiencies in the EPD response in pulsed beams have been reported. The feasibility of using a medical X-ray machine to perform EPD tests was studied. Reference dosimeters were verified and EPD testing procedure was established.
art ic l e i nf o
a b s t r a c t
Article history: Received 10 July 2013 Accepted 25 October 2013
Electronic personal dosimeters (EPD) based on solid state detectors have been used for personnel monitoring for radiation protection purpose; their use has been extended to practices with pulsed radiation beams although their performance is not well known. Deficiencies in the EPD response in pulsed radiation fields have been reported; they were not detected before since type tests and calibrations of EPDs were established in terms of continuous X and gamma reference radiations. An ISO working group was formed to elaborate a standard for test conditions and performance requirements of EPDs in pulsed beams; the PTB/Germany implemented a special X-ray facility for generating the reference pulsed radiation beams. In this work, an 800 Plus VMI medical X-ray machine of the Dosimeter Calibration Laboratory of CDTN/CNEN was characterized to verify its feasibility to perform EPD tests. Characterization of the x-ray beam was done in terms of practical peak voltage, half-value layer, mean energy and air kerma rate. Reference dosimeters used for air kerma measurements were verified as far their metrological coherence and a procedure for testing EDPs was established. & 2013 Elsevier Ltd. All rights reserved.
Keywords: Pulsed X-rays Electronic personal dosimeters Dosimeter response Dosimeter tests
1. Introduction Personal radiation monitoring is a basic procedure to verify the compliance to regulatory requirements for radiological protection. The great diversity of field radiation conditions that is found in industry, research laboratories and hospitals requires the knowledge of the metrological characteristics for an adequate choice of a radiation dosimeter (Burges, 2001). Electronic personal dosimeters (EPD) based on solid state detectors have largely been used for personnel monitoring in practices; they are a practical tool for optimization since they
n Corresponding author at: Development Center of Nuclear Technology, CDTN/ CNEN, Service of Radiation Applied to Health, Av. Presidente Antonio Carlos 6627, Campus UFMG, Pampullha, 30901-270 Belo Horizonte, Minas Gerais, Brazil. Tel.: þ 55 3130693121. E-mail addresses: [email protected], [email protected] (T.A. Da Silva).
provide the dose rate in the real time and the radiation dose immediately after any task related to radiation exposure. Their use have been extended to pulsed radiation beams that are found in accelerators and X-ray machines used for diagnostic radiology. Since type tests and calibrations of EPDs were established to be performed in continuous X- and gamma radiation beams, the performance of EPDs in pulsed beams is still unknown and deficiencies in their response were reported (Ankerhold et al., 2009). The ISO and IEC organizations started a working group to produce a standard for type testing and calibrating EPDs in pulsed beams. The German Primary Laboratory – PTB – installed a novel facility for generating reference pulsed X-ray beams (Klammer et al., 2012). In Brazil, there is no perspective for installing a special laboratory to reproduce reference pulsed beams. In this work, an 800 Plus VMI medical X-ray machine of the Dosimeter Calibration
0969-806X/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.radphyschem.2013.10.019
Please cite this article as: Guimarães, M.C., Da Silva, T.A., Characterization of a medical X-ray machine for testing the response of electronic dosimeters in pulsed radiation fields. Radiat. Phys. Chem. (2013), http://dx.doi.org/10.1016/j.radphyschem.2013.10.019i
M.C. Guimarães, T.A. Da Silva / Radiation Physics and Chemistry ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
Laboratory of CDTN/CNEN was characterized to verify its feasibility of testing EPDs.
2. Materials and methods An 800 Plus VMI medical X-ray machine with 1.9 mm Al inherent filtration, 50–150 kV tube potential range was used in this work. RQA beam qualities established by IEC (2005) were considered to represent the transmitted and scattered radiation beams that would reach an electronic personal dosimeter during a specific diagnostic radiology practice. As far as possible, RQA beam qualities were reproduced in the CDTN calibration laboratory; high-purity Goodfellow aluminum absorbers were used as additional filtration. Beam characterization was done by determining the practical peak voltage with a PTB calibrated Diavolt, the halfvalue layers and mean energies with the Xcomp5R software and the air kerma rates with reference dosimeters. A 10 6-6 Accu-Gold RADCAL ionization chamber and Xi light UNFORS solid state dosimetric system were investigated to be used as reference dosimeters. Their reliability was verified in terms of repeatability of air kerma measurements and leakage current influence; their traceability was assured through a calibration traceable to a primary laboratory. The metrological coherence between both reference dosimeters was studied by comparing them in RQA qualities that were implemented in a constant potential Seifert–Pantak X-ray machine (Da Silva et al., 2011.). They were also compared in the pulsed beams from the VMI medical X-ray machine. Fig. 1 shows the X-ray setup of the Seifert– Pantak and the VMI X-ray machines used for the comparison procedures.
are shown in Table 3. Differences between air kerma rate measurements with both reference dosimeters were lower than 2% for RQA-5 and 7 qualities; although it reached 17% to the RQA-9 quality, it was not considered relevant for testing personal dosimeters to be used for radiation protection purposes. Table 4 shows the results of the comparison between the reference dosimeters in the air kerma rate measurements in the pulsed beams from the VMI X-ray machine. Measurements were done in the RQA quality for exposure times of 50, 100, 150 and 300 ms and tube current of 50, 100, 150 and 300 mA. Results showed that the reference dosimeters agreed within 2% for all exposure conditions. Based on the results, the following calibration procedure was established: RQA qualities would be reproduced in the VMI X-ray medical machine; air kerma rates would be measured with the 10 6-6 Accu-Gold RADCAL ionization chamber that must be traceable to a national laboratory; the Xi light UNFORS dosimeter would be used as a monitor dosimeter at the border of the ISO slab phantom during EPD exposures; published RQA conversion coefficients from air kerma to personal dose equivalent should be used. Fig. 2 shows the setup for testing the EPD dosimeters in terms of personal dose equivalent. Table 1 Characteristic parameters of the beam qualities implemented in the constant potential Seifert–Pantak X-ray machine (Da Silva et al., 2011). Beam quality
Practical peak voltage (kV)
Additional filtration (mm Al)
Half-value layer (mm Al)
RQA-5 RQA-7 RQA-9
71.4 90.9 121.3
19.6 29.7 38.5
6.8 9.2 11.7
3. Results and discussion The values of the X-ray beam parameters of the RQA qualities implemented in the constant potential Seifert–Pantak and in the pulsed VMI machines are shown in Tables 1 and 2. Although X-ray beam parameters were not equal to IEC values (IEC, 2005), as the half-value layers agreed within the acceptable limit of 5%, X-ray qualities could be considered to be similar to IEC qualities. Results of the comparison between the reference dosimeters during simultaneous measurements of the air kerma rates in RQA qualities in the constant potential Seifert–Pantak X-ray machine
Table 2 Characteristic parameters of the beam qualities implemented in the VMI medical X-ray machine. Beam quality
Nominal voltage (kV)
Additional filtration Mean energy Half-value layer (mm Al) (keV) (mm Al)
RQA-5 RQA-7 RQA-9
70 90 120
21.0 30.0 40.0
51.2 62.4 75.8
6.44 8.94 11.35
Fig. 1. X-ray setup of the constant potential Seifert-Pantak machine (left) and of the pulsed VMI machine (right) for verification of the metrological coherence between the reference dosimeters.
Please cite this article as: Guimarães, M.C., Da Silva, T.A., Characterization of a medical X-ray machine for testing the response of electronic dosimeters in pulsed radiation fields. Radiat. Phys. Chem. (2013), http://dx.doi.org/10.1016/j.radphyschem.2013.10.019i
M.C. Guimarães, T.A. Da Silva / Radiation Physics and Chemistry ∎ (∎∎∎∎) ∎∎∎–∎∎∎
3
Table 3 Air kerma rate measurements with Xi light UNFORS dosimetric system and 10 6-6 Accu-Gold RADCAL ionization chamber in a constant potential X-ray machine. Beam quality
RQA-5 RQA-7 RQA-9
Air kerma rate (mGy/min) UNFORS
RADCAL
2.26 2.16 2.93
2.31 2.19 3.52
Ratio relative to RADCAL dosimeter
0.978 0.986 0.832
Table 4 Air kerma rate measurements with UNFORS and RADCAL reference dosimeters in a RQA-9 quality from the pulsed beam from the VMI X-ray machine. Exposure time (ms)
50 150 300 100 100 100
Tube current (mA)
100 100 100 50 150 300
Air kerma rate (mGy/s)
Ratio relative to RADCAL dosimeter
RADCAL
UNFORS
0.0980 0.109 0.116 0.0487 0.153 0.469
0.0983 0.107 0.114 0.0482 0.151 0.462
0.997 1.019 1.018 1.010 1.013 1.015
Fig. 2. X-ray setup with the pulsed VMI machine (left) for testing the EPD dosimeters on the ISO slab phantom (right) in terms of personal dose equivalent.
4. Conclusion
References
The VMI medical X-ray machine, the irradiation setup and the calibration procedure seemed to be feasible for testing EPDs in pulsed beams. The next step of this work will be to test selected dosimeters taking into account their specific dose and energy ranges.
Ankerhold, U., Hupe, O., Ambrosi, P., 2009. Deficiencies of active electronic radiation protection dosemeters in pulsed fields. Radiat. Prot. Dosim. 135 (3), 149–153. Burges, P.H. Guidance on the choice, use and maintenance of hand-held radiation monitoring equipment. NRPB- R326, Didcot, UK (2001). Da Silva, T.A., Oliveira, P.M.C., Pereira, F.J., Bastos, V.C., Souza, L.J., Squair, P.L., Baptista Neto, A.T., Soares, C.M.A., Nogueira Tavares, M.S. and Alonso, T.C. Implementation of a metrological framework for dosimetry of X-ray beams used in diagnostic radiology in Minas Gerais, Brazil. Standards, applications and quality assurance in medical radiation dosimetry (IDOS). In: Proceedings of an International Symposium, STI/PUB/1514, International Atomic Energy Agency, Vienna (2011). IEC. International Electrotechnical Commission – Medical diagnostic X-ray equipment – radiation conditions for use in the determination of characteristics. Rep. IEC-61627, Geneva (2005). Klammer, J., Roth., J., Hupe, O., 2012. Novel reference radiation fields for pulsed photon radition installed at PTB. Radiat. Prot. Dosim. 151 (3), 478–482.
Acknowledgments Margarete C. Guimarães is thankful to the CNEN for providing her with a M.Sc. fellowship. This work was supported by FINEP (SIBRATEC) and FAPEMIG (PPM); it is part of the project INCT Radiation Metrology in Medicine.
Please cite this article as: Guimarães, M.C., Da Silva, T.A., Characterization of a medical X-ray machine for testing the response of electronic dosimeters in pulsed radiation fields. Radiat. Phys. Chem. (2013), http://dx.doi.org/10.1016/j.radphyschem.2013.10.019i
Contents lists available at ScienceDirect
Radiation Physics and Chemistry journal homepage: www.elsevier.com/locate/radphyschem
Characterization of a medical X-ray machine for testing the response of electronic dosimeters in pulsed radiation fields Margarete C. Guimarães a, Teógenes A. Da Silva a,b,n a b
Postgraduation Course of Science and Technology of Radiations, Minerals and Materials, CDTN/CNEN, Belo Horizonte, Brazil Development Center of Nuclear Technology, CDTN/CNEN, Belo Horizonte, Brazil
H I G H L I G H T S
Electronic personal dosimeters (EPD) have been used for personnel monitoring. EPD use has been extended to pulsed radiation beams. Deficiencies in the EPD response in pulsed beams have been reported. The feasibility of using a medical X-ray machine to perform EPD tests was studied. Reference dosimeters were verified and EPD testing procedure was established.
art ic l e i nf o
a b s t r a c t
Article history: Received 10 July 2013 Accepted 25 October 2013
Electronic personal dosimeters (EPD) based on solid state detectors have been used for personnel monitoring for radiation protection purpose; their use has been extended to practices with pulsed radiation beams although their performance is not well known. Deficiencies in the EPD response in pulsed radiation fields have been reported; they were not detected before since type tests and calibrations of EPDs were established in terms of continuous X and gamma reference radiations. An ISO working group was formed to elaborate a standard for test conditions and performance requirements of EPDs in pulsed beams; the PTB/Germany implemented a special X-ray facility for generating the reference pulsed radiation beams. In this work, an 800 Plus VMI medical X-ray machine of the Dosimeter Calibration Laboratory of CDTN/CNEN was characterized to verify its feasibility to perform EPD tests. Characterization of the x-ray beam was done in terms of practical peak voltage, half-value layer, mean energy and air kerma rate. Reference dosimeters used for air kerma measurements were verified as far their metrological coherence and a procedure for testing EDPs was established. & 2013 Elsevier Ltd. All rights reserved.
Keywords: Pulsed X-rays Electronic personal dosimeters Dosimeter response Dosimeter tests
1. Introduction Personal radiation monitoring is a basic procedure to verify the compliance to regulatory requirements for radiological protection. The great diversity of field radiation conditions that is found in industry, research laboratories and hospitals requires the knowledge of the metrological characteristics for an adequate choice of a radiation dosimeter (Burges, 2001). Electronic personal dosimeters (EPD) based on solid state detectors have largely been used for personnel monitoring in practices; they are a practical tool for optimization since they
n Corresponding author at: Development Center of Nuclear Technology, CDTN/ CNEN, Service of Radiation Applied to Health, Av. Presidente Antonio Carlos 6627, Campus UFMG, Pampullha, 30901-270 Belo Horizonte, Minas Gerais, Brazil. Tel.: þ 55 3130693121. E-mail addresses: [email protected], [email protected] (T.A. Da Silva).
provide the dose rate in the real time and the radiation dose immediately after any task related to radiation exposure. Their use have been extended to pulsed radiation beams that are found in accelerators and X-ray machines used for diagnostic radiology. Since type tests and calibrations of EPDs were established to be performed in continuous X- and gamma radiation beams, the performance of EPDs in pulsed beams is still unknown and deficiencies in their response were reported (Ankerhold et al., 2009). The ISO and IEC organizations started a working group to produce a standard for type testing and calibrating EPDs in pulsed beams. The German Primary Laboratory – PTB – installed a novel facility for generating reference pulsed X-ray beams (Klammer et al., 2012). In Brazil, there is no perspective for installing a special laboratory to reproduce reference pulsed beams. In this work, an 800 Plus VMI medical X-ray machine of the Dosimeter Calibration
0969-806X/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.radphyschem.2013.10.019
Please cite this article as: Guimarães, M.C., Da Silva, T.A., Characterization of a medical X-ray machine for testing the response of electronic dosimeters in pulsed radiation fields. Radiat. Phys. Chem. (2013), http://dx.doi.org/10.1016/j.radphyschem.2013.10.019i
M.C. Guimarães, T.A. Da Silva / Radiation Physics and Chemistry ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
Laboratory of CDTN/CNEN was characterized to verify its feasibility of testing EPDs.
2. Materials and methods An 800 Plus VMI medical X-ray machine with 1.9 mm Al inherent filtration, 50–150 kV tube potential range was used in this work. RQA beam qualities established by IEC (2005) were considered to represent the transmitted and scattered radiation beams that would reach an electronic personal dosimeter during a specific diagnostic radiology practice. As far as possible, RQA beam qualities were reproduced in the CDTN calibration laboratory; high-purity Goodfellow aluminum absorbers were used as additional filtration. Beam characterization was done by determining the practical peak voltage with a PTB calibrated Diavolt, the halfvalue layers and mean energies with the Xcomp5R software and the air kerma rates with reference dosimeters. A 10 6-6 Accu-Gold RADCAL ionization chamber and Xi light UNFORS solid state dosimetric system were investigated to be used as reference dosimeters. Their reliability was verified in terms of repeatability of air kerma measurements and leakage current influence; their traceability was assured through a calibration traceable to a primary laboratory. The metrological coherence between both reference dosimeters was studied by comparing them in RQA qualities that were implemented in a constant potential Seifert–Pantak X-ray machine (Da Silva et al., 2011.). They were also compared in the pulsed beams from the VMI medical X-ray machine. Fig. 1 shows the X-ray setup of the Seifert– Pantak and the VMI X-ray machines used for the comparison procedures.
are shown in Table 3. Differences between air kerma rate measurements with both reference dosimeters were lower than 2% for RQA-5 and 7 qualities; although it reached 17% to the RQA-9 quality, it was not considered relevant for testing personal dosimeters to be used for radiation protection purposes. Table 4 shows the results of the comparison between the reference dosimeters in the air kerma rate measurements in the pulsed beams from the VMI X-ray machine. Measurements were done in the RQA quality for exposure times of 50, 100, 150 and 300 ms and tube current of 50, 100, 150 and 300 mA. Results showed that the reference dosimeters agreed within 2% for all exposure conditions. Based on the results, the following calibration procedure was established: RQA qualities would be reproduced in the VMI X-ray medical machine; air kerma rates would be measured with the 10 6-6 Accu-Gold RADCAL ionization chamber that must be traceable to a national laboratory; the Xi light UNFORS dosimeter would be used as a monitor dosimeter at the border of the ISO slab phantom during EPD exposures; published RQA conversion coefficients from air kerma to personal dose equivalent should be used. Fig. 2 shows the setup for testing the EPD dosimeters in terms of personal dose equivalent. Table 1 Characteristic parameters of the beam qualities implemented in the constant potential Seifert–Pantak X-ray machine (Da Silva et al., 2011). Beam quality
Practical peak voltage (kV)
Additional filtration (mm Al)
Half-value layer (mm Al)
RQA-5 RQA-7 RQA-9
71.4 90.9 121.3
19.6 29.7 38.5
6.8 9.2 11.7
3. Results and discussion The values of the X-ray beam parameters of the RQA qualities implemented in the constant potential Seifert–Pantak and in the pulsed VMI machines are shown in Tables 1 and 2. Although X-ray beam parameters were not equal to IEC values (IEC, 2005), as the half-value layers agreed within the acceptable limit of 5%, X-ray qualities could be considered to be similar to IEC qualities. Results of the comparison between the reference dosimeters during simultaneous measurements of the air kerma rates in RQA qualities in the constant potential Seifert–Pantak X-ray machine
Table 2 Characteristic parameters of the beam qualities implemented in the VMI medical X-ray machine. Beam quality
Nominal voltage (kV)
Additional filtration Mean energy Half-value layer (mm Al) (keV) (mm Al)
RQA-5 RQA-7 RQA-9
70 90 120
21.0 30.0 40.0
51.2 62.4 75.8
6.44 8.94 11.35
Fig. 1. X-ray setup of the constant potential Seifert-Pantak machine (left) and of the pulsed VMI machine (right) for verification of the metrological coherence between the reference dosimeters.
Please cite this article as: Guimarães, M.C., Da Silva, T.A., Characterization of a medical X-ray machine for testing the response of electronic dosimeters in pulsed radiation fields. Radiat. Phys. Chem. (2013), http://dx.doi.org/10.1016/j.radphyschem.2013.10.019i
M.C. Guimarães, T.A. Da Silva / Radiation Physics and Chemistry ∎ (∎∎∎∎) ∎∎∎–∎∎∎
3
Table 3 Air kerma rate measurements with Xi light UNFORS dosimetric system and 10 6-6 Accu-Gold RADCAL ionization chamber in a constant potential X-ray machine. Beam quality
RQA-5 RQA-7 RQA-9
Air kerma rate (mGy/min) UNFORS
RADCAL
2.26 2.16 2.93
2.31 2.19 3.52
Ratio relative to RADCAL dosimeter
0.978 0.986 0.832
Table 4 Air kerma rate measurements with UNFORS and RADCAL reference dosimeters in a RQA-9 quality from the pulsed beam from the VMI X-ray machine. Exposure time (ms)
50 150 300 100 100 100
Tube current (mA)
100 100 100 50 150 300
Air kerma rate (mGy/s)
Ratio relative to RADCAL dosimeter
RADCAL
UNFORS
0.0980 0.109 0.116 0.0487 0.153 0.469
0.0983 0.107 0.114 0.0482 0.151 0.462
0.997 1.019 1.018 1.010 1.013 1.015
Fig. 2. X-ray setup with the pulsed VMI machine (left) for testing the EPD dosimeters on the ISO slab phantom (right) in terms of personal dose equivalent.
4. Conclusion
References
The VMI medical X-ray machine, the irradiation setup and the calibration procedure seemed to be feasible for testing EPDs in pulsed beams. The next step of this work will be to test selected dosimeters taking into account their specific dose and energy ranges.
Ankerhold, U., Hupe, O., Ambrosi, P., 2009. Deficiencies of active electronic radiation protection dosemeters in pulsed fields. Radiat. Prot. Dosim. 135 (3), 149–153. Burges, P.H. Guidance on the choice, use and maintenance of hand-held radiation monitoring equipment. NRPB- R326, Didcot, UK (2001). Da Silva, T.A., Oliveira, P.M.C., Pereira, F.J., Bastos, V.C., Souza, L.J., Squair, P.L., Baptista Neto, A.T., Soares, C.M.A., Nogueira Tavares, M.S. and Alonso, T.C. Implementation of a metrological framework for dosimetry of X-ray beams used in diagnostic radiology in Minas Gerais, Brazil. Standards, applications and quality assurance in medical radiation dosimetry (IDOS). In: Proceedings of an International Symposium, STI/PUB/1514, International Atomic Energy Agency, Vienna (2011). IEC. International Electrotechnical Commission – Medical diagnostic X-ray equipment – radiation conditions for use in the determination of characteristics. Rep. IEC-61627, Geneva (2005). Klammer, J., Roth., J., Hupe, O., 2012. Novel reference radiation fields for pulsed photon radition installed at PTB. Radiat. Prot. Dosim. 151 (3), 478–482.
Acknowledgments Margarete C. Guimarães is thankful to the CNEN for providing her with a M.Sc. fellowship. This work was supported by FINEP (SIBRATEC) and FAPEMIG (PPM); it is part of the project INCT Radiation Metrology in Medicine.
Please cite this article as: Guimarães, M.C., Da Silva, T.A., Characterization of a medical X-ray machine for testing the response of electronic dosimeters in pulsed radiation fields. Radiat. Phys. Chem. (2013), http://dx.doi.org/10.1016/j.radphyschem.2013.10.019i