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Long-term stability evaluation of user-derived electrometer calibration factors (kelec, user) for radiotherapy dosimetry.

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Τίτλος: Long-term stability evaluation of user-derived electrometer calibration factors (kelec, user) for radiotherapy dosimetry.
Συγγραφείς: Tsuno H; Gunma Prefectural College of Health Sciences, Maebashi, Gunma, JAPAN.; Department of Radiation Oncology, Japanese Red Cross Maebashi Hospital, Maebashi, Gunma, JAPAN., Sasaki K; Graduate School of Radiological Technology, Gunma Prefectural College of Health Sciences, Maebashi, Gunma, JAPAN., Sasaki R; Department of Radiology, National Hospital Organization Sendai Medical Center, Sendai, Miyagi, JAPAN., Matsubayashi F; Department of Radiation Oncology, Cancer Institute Hospital, Japanese Foundation for Cancer Research, Tokyo, JAPAN., Nishi K; Department of Radiology, JR Tokyo General Hospital, Tokyo, JAPAN., Ushikawa T; Department of Radiology, JR Tokyo General Hospital, Tokyo, JAPAN., Goto D; Department of Radiology, JR Tokyo General Hospital, Tokyo, JAPAN., Kosugi R; Department of Radiology, Hamamatsu University School of Medicine, Hamamatsu, Shizuoka, JAPAN., Kawashima Y; Department of Medical Technology, Japanese Red Cross Maebashi Hospital, Maebashi, Gunma, JAPAN.
Πηγή: Journal of applied clinical medical physics [J Appl Clin Med Phys] 2026 Oct; Vol. 27 (10), pp. e70840.
Τύπος έκδοσης: Journal Article; Evaluation Study
Γλώσσα: English
Στοιχεία περιοδικού: Publisher: Wiley on behalf of American Association of Physicists in Medicine Country of Publication: United States NLM ID: 101089176 Publication Model: Print Cited Medium: Internet ISSN: 1526-9914 (Electronic) Linking ISSN: 15269914 NLM ISO Abbreviation: J Appl Clin Med Phys Subsets: MEDLINE
Imprint Name(s): Publication: 2017- : Malden, MA : Wiley on behalf of American Association of Physicists in Medicine
Original Publication: Reston, VA : American College of Medical Physics, c2000-
Ιατρικοί όροι (MeSH): Radiometry*/methods , Radiometry*/instrumentation , Radiometry*/standards , Particle Accelerators*/instrumentation , Quality Assurance, Health Care*/standards , Radiotherapy Planning, Computer-Assisted*/methods , Phantoms, Imaging*, Calibration/standards ; Radiotherapy, Intensity-Modulated/methods ; Humans ; Radiotherapy Dosage ; Uncertainty
Περίληψη: Purpose: User-derived electrometer calibration factors (kelec, user) have been proposed as a practical approach for electrometer quality assurance in radiotherapy dosimetry. However, the contribution of long-term stability to the uncertainty of kelec, user has not been quantitatively evaluated. This study aimed to assess the long-term stability of kelec, user over a 28-month period and to validate the method using different signal input techniques.
Methods: A RAMTEC Solo electrometer was used as the reference electrometer, and three electrometers (UNIDOSwebline, RAMTEC Duo, and Super MAX) were evaluated as electrometers under test. Electrometer sensitivity ratios were measured using three signal input methods: A LINAC-based method, a battery-powered current source (SCG002), and a servo-controlled current source (EMF521R). User-derived calibration factors were calculated from the sensitivity ratios and the calibration coefficient of the reference electrometer. Long-term stability was evaluated from repeated measurements over 28 months using linear regression analysis, and the associated uncertainty component was estimated according to the Guide to the Expression of Uncertainty in Measurement (GUM).
Results: The coefficients of variation for repeated measurements were ≤ 0.071% for all methods. The kelec, user values obtained using the LINAC method, SCG002, and EMF521R agreed within 0.1%, with a maximum relative difference of 0.06%. Over the 28-month observation period, the largest estimated drift was 1.84 × 10- 4, corresponding to a Type B standard uncertainty of 1.06 × 10- 4 (1.06 × 10- 2%). The combined standard uncertainty of kelec, user remained 0.20%, and the experimentally determined long-term stability component had a negligible effect on the overall uncertainty.
Conclusions: The influence of signal input method on kelec, user was minimal, and consistent results were obtained using LINAC-based and current-source-based measurements. The uncertainty contribution from long-term stability over 28 months was negligible compared with the reported uncertainty of electrometer calibration factors. These findings support the use of periodic in-house sensitivity comparison measurements as a complementary quality assurance tool for monitoring electrometer performance between external calibrations. These findings extend previous studies by providing quantitative evidence of the relative sensitivity stability of user-derived electrometer calibration factors and thereby support their application for routine in-house quality assurance.
(© 2026 The Author(s). Journal of Applied Clinical Medical Physics published by Wiley Periodicals, LLC on behalf of The American Association of Physicists in Medicine.)
References: Cunningham J, Cohen M, Dutreix A. Determination of Absorbed Dose in a Patient Irradiated by Beams of X‐ or Gamma‐Rays in Radiotherapy Procedures. International Commission on Radiation Units and Measurement; 1976. ICRU Report.
International Electrotechnical Commission (IEC). Medical electrical equipment—Dosimeters with ionization chambers as used in radiotherapy. Geneva International Electrotechnical Commission; 2011 IEC 60731 :2011.
McEwen M, DeWerd L, Ibbott G, et al. Addendum to the AAPM's TG‐51 protocol for clinical reference dosimetry of high‐energy photon beams. Med Phys. 2014;41(4):041501. doi:10.1118/1.4866223.
Morgan AM, Aird EG, Aukett RJ, et al. IPEM guidelines on dosimeter systems for use as transfer instruments between the UK primary dosimetry standards laboratory (NPL) and radiotherapy centres. Phys Med Biol. 2000;45(9):2445‐2457.
Blad B, Wendel P, Nilsson P. A simple test device for electrometers. Phys Med Biol. 1998;43(8):2385‐2391.
Matsubayashi F, Tsuno H, Matsumoto K, et al. Current generator for precision control of electrometer, precision control system, and calibration method. Japan, 2021: Patent 6989834.
Kawashima T, Varnava M, Ozawa S, et al. Measurement and evaluation of electrometer correction factors using a charge generator. J Appl Clin Med Phys. 2023;24(8):e14082. doi:10.1002/acm2.14082.
Tsuno H, Matsubayashi F, Sasaki K, Sakai T, Matsumoto K, Takeuchi K. Verification of response uncertainty in electrometers through cross‐comparison with a novel current source: a comparative study with guidelines for electrometers used in radiation therapy dosimeters. Jpn J Med Phys. 2024;44(2):21‐28. doi:10.11323/jjmp.44.2_21.
Tsuno H, Matsubayashi F, Sasaki K, Sakai T, Matsumoto K, Takeuchi K. Evaluation on the availability of the electrometer inspection by users using a newly developed current source. Radiol Technol. 2023;79(2):166‐176. doi:10.6009/jjrt.2023‐1216. Japanese.
Tsuno H, Sasaki R, Sasaki K, et al. Feasibility study of in‐house second‐channel calibration of dual‐channel electrometers using a battery‐powered current source. J Appl Clin Med Phys Vol. 2026;27(3):e70476.
Li G, Xiong J, Sun S, et al. Validation of virtual sensor‐assisted Bayesian inference‐based in‐situ sensor calibration strategy for building HVAC systems. Build Simul. 2023;16(2):185‐203. doi:10.1007/s12273‐022‐0935‐7.
Deng H, Wang J, Zhang H, Zhang J, Ma M, Zhong X. An in‐situ self‐calibration method for non‐contact full‐field strain measurement. Measurement. 2020;162:107871. doi:10.1016/j.measurement.2020.107871.
Koo J, Yoon S, Kim J. Virtual in situ calibration for operational backup virtual sensors in building energy systems. Energies. 2022;15(4):1394. doi:10.3390/en15041394.
Joint Committee for Guides in Metrology (JCGM). Evaluation of Measurement Data—Guide to the Expression of Uncertainty in Measurement (GUM). JCGM 100:2008. JCGM; 2008. doi:10.59161/JCGM100‐2008E.
Tsuno H, Sasaki K, Matsubayashi F, et al. New idea for determining the optimal number of measurements in absorbed dose‐to‐water measurement of high‐energy photon beam. Radiat Prot Dosimetry. 2022;199(3):246‐253. doi:10.1093/rpd/ncac262.
Tsuno H, Maruyama D, Sasaki K, Matsubayashi F. Optimising the number of measurements for absorbed dose‐to‐water calibration coefficient of ionization chamber by cross‐calibration using high‐energy electron beams. J Radioanal Nucl Chem. 2026;335:4335‐4341. doi:10.1007/s10967‐026‐10921‐0.
Castro P, García‐Vicente F, Mínguez C, et al. Study of the uncertainty in the determination of the absorbed dose to water during external beam radiotherapy calibration. J Appl Clin Med Phys. 2008;9(1):70‐86. doi:10.1120/jacmp.v9i1.2676.
Contributed Indexing: Keywords: electrometer; electrometer calibration; long‐term stability; quality assurance; radiotherapy dosimetry
Entry Date(s): Date Created: 20261008 Date Completed: 20261008 Latest Revision: 20261010
Update Code: 20261010
PubMed Central ID: PMC13648246
DOI: 10.1002/acm2.70840
PMID: 42847865
Βάση Δεδομένων: MEDLINE
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  Data: Long-term stability evaluation of user-derived electrometer calibration factors (k<subscript>elec, user</subscript>) for radiotherapy dosimetry.
– Name: Author
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  Data: <searchLink fieldCode="AU" term="%22Tsuno+H%22">Tsuno H</searchLink>; Gunma Prefectural College of Health Sciences, Maebashi, Gunma, JAPAN.; Department of Radiation Oncology, Japanese Red Cross Maebashi Hospital, Maebashi, Gunma, JAPAN.<br /><searchLink fieldCode="AU" term="%22Sasaki+K%22">Sasaki K</searchLink>; Graduate School of Radiological Technology, Gunma Prefectural College of Health Sciences, Maebashi, Gunma, JAPAN.<br /><searchLink fieldCode="AU" term="%22Sasaki+R%22">Sasaki R</searchLink>; Department of Radiology, National Hospital Organization Sendai Medical Center, Sendai, Miyagi, JAPAN.<br /><searchLink fieldCode="AU" term="%22Matsubayashi+F%22">Matsubayashi F</searchLink>; Department of Radiation Oncology, Cancer Institute Hospital, Japanese Foundation for Cancer Research, Tokyo, JAPAN.<br /><searchLink fieldCode="AU" term="%22Nishi+K%22">Nishi K</searchLink>; Department of Radiology, JR Tokyo General Hospital, Tokyo, JAPAN.<br /><searchLink fieldCode="AU" term="%22Ushikawa+T%22">Ushikawa T</searchLink>; Department of Radiology, JR Tokyo General Hospital, Tokyo, JAPAN.<br /><searchLink fieldCode="AU" term="%22Goto+D%22">Goto D</searchLink>; Department of Radiology, JR Tokyo General Hospital, Tokyo, JAPAN.<br /><searchLink fieldCode="AU" term="%22Kosugi+R%22">Kosugi R</searchLink>; Department of Radiology, Hamamatsu University School of Medicine, Hamamatsu, Shizuoka, JAPAN.<br /><searchLink fieldCode="AU" term="%22Kawashima+Y%22">Kawashima Y</searchLink>; Department of Medical Technology, Japanese Red Cross Maebashi Hospital, Maebashi, Gunma, JAPAN.
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  Data: <searchLink fieldCode="JN" term="%22101089176%22">Journal of applied clinical medical physics</searchLink> [J Appl Clin Med Phys] 2026 Oct; Vol. 27 (10), pp. e70840.
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  Data: <i>Publisher: </i><searchLink fieldCode="PB" term="%22Wiley+on+behalf+of+American+Association+of+Physicists+in+Medicine%22">Wiley on behalf of American Association of Physicists in Medicine </searchLink><i>Country of Publication: </i>United States <i>NLM ID: </i>101089176 <i>Publication Model: </i>Print <i>Cited Medium: </i>Internet <i>ISSN: </i>1526-9914 (Electronic) <i>Linking ISSN: </i><searchLink fieldCode="IS" term="%2215269914%22">15269914 </searchLink><i>NLM ISO Abbreviation: </i>J Appl Clin Med Phys <i>Subsets: </i>MEDLINE
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  Data: <i>Publication</i>: 2017- : Malden, MA : Wiley on behalf of American Association of Physicists in Medicine<br /><i>Original Publication</i>: Reston, VA : American College of Medical Physics, c2000-
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  Data: <searchLink fieldCode="MM" term="%22Radiometry%22">Radiometry*</searchLink>/<searchLink fieldCode="MM" term="%22Radiometry+methods%22">methods</searchLink> <br /><searchLink fieldCode="MM" term="%22Radiometry%22">Radiometry*</searchLink>/<searchLink fieldCode="MM" term="%22Radiometry+instrumentation%22">instrumentation</searchLink> <br /><searchLink fieldCode="MM" term="%22Radiometry%22">Radiometry*</searchLink>/<searchLink fieldCode="MM" term="%22Radiometry+standards%22">standards</searchLink> <br /><searchLink fieldCode="MM" term="%22Particle+Accelerators%22">Particle Accelerators*</searchLink>/<searchLink fieldCode="MM" term="%22Particle+Accelerators+instrumentation%22">instrumentation</searchLink> <br /><searchLink fieldCode="MM" term="%22Quality+Assurance%2C+Health+Care%22">Quality Assurance, Health Care*</searchLink>/<searchLink fieldCode="MM" term="%22Quality+Assurance%2C+Health+Care+standards%22">standards</searchLink> <br /><searchLink fieldCode="MM" term="%22Radiotherapy+Planning%2C+Computer-Assisted%22">Radiotherapy Planning, Computer-Assisted*</searchLink>/<searchLink fieldCode="MM" term="%22Radiotherapy+Planning%2C+Computer-Assisted+methods%22">methods</searchLink> <br /><searchLink fieldCode="MM" term="%22Phantoms%2C+Imaging%22">Phantoms, Imaging*</searchLink><br /><searchLink fieldCode="MH" term="%22Calibration%22">Calibration</searchLink>/<searchLink fieldCode="MH" term="%22Calibration+standards%22">standards</searchLink> ; <searchLink fieldCode="MH" term="%22Radiotherapy%2C+Intensity-Modulated%22">Radiotherapy, Intensity-Modulated</searchLink>/<searchLink fieldCode="MH" term="%22Radiotherapy%2C+Intensity-Modulated+methods%22">methods</searchLink> ; <searchLink fieldCode="MH" term="%22Humans%22">Humans</searchLink> ; <searchLink fieldCode="MH" term="%22Radiotherapy+Dosage%22">Radiotherapy Dosage</searchLink> ; <searchLink fieldCode="MH" term="%22Uncertainty%22">Uncertainty</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: Purpose: User-derived electrometer calibration factors (k<subscript>elec, user</subscript>) have been proposed as a practical approach for electrometer quality assurance in radiotherapy dosimetry. However, the contribution of long-term stability to the uncertainty of k<subscript>elec, user</subscript> has not been quantitatively evaluated. This study aimed to assess the long-term stability of k<subscript>elec, user</subscript> over a 28-month period and to validate the method using different signal input techniques.<br />Methods: A RAMTEC Solo electrometer was used as the reference electrometer, and three electrometers (UNIDOS<superscript>webline</superscript>, RAMTEC Duo, and Super MAX) were evaluated as electrometers under test. Electrometer sensitivity ratios were measured using three signal input methods: A LINAC-based method, a battery-powered current source (SCG002), and a servo-controlled current source (EMF521R). User-derived calibration factors were calculated from the sensitivity ratios and the calibration coefficient of the reference electrometer. Long-term stability was evaluated from repeated measurements over 28 months using linear regression analysis, and the associated uncertainty component was estimated according to the Guide to the Expression of Uncertainty in Measurement (GUM).<br />Results: The coefficients of variation for repeated measurements were ≤ 0.071% for all methods. The k<subscript>elec, user</subscript> values obtained using the LINAC method, SCG002, and EMF521R agreed within 0.1%, with a maximum relative difference of 0.06%. Over the 28-month observation period, the largest estimated drift was 1.84 × 10<superscript>-</superscript> <superscript>4</superscript>, corresponding to a Type B standard uncertainty of 1.06 × 10<superscript>-</superscript> <superscript>4</superscript> (1.06 × 10<superscript>-</superscript> <superscript>2</superscript>%). The combined standard uncertainty of k<subscript>elec, user</subscript> remained 0.20%, and the experimentally determined long-term stability component had a negligible effect on the overall uncertainty.<br />Conclusions: The influence of signal input method on k<subscript>elec, user</subscript> was minimal, and consistent results were obtained using LINAC-based and current-source-based measurements. The uncertainty contribution from long-term stability over 28 months was negligible compared with the reported uncertainty of electrometer calibration factors. These findings support the use of periodic in-house sensitivity comparison measurements as a complementary quality assurance tool for monitoring electrometer performance between external calibrations. These findings extend previous studies by providing quantitative evidence of the relative sensitivity stability of user-derived electrometer calibration factors and thereby support their application for routine in-house quality assurance.<br /> (© 2026 The Author(s). Journal of Applied Clinical Medical Physics published by Wiley Periodicals, LLC on behalf of The American Association of Physicists in Medicine.)
– Name: Ref
  Label: References
  Group: RefInfo
  Data: Cunningham J, Cohen M, Dutreix A. Determination of Absorbed Dose in a Patient Irradiated by Beams of X‐ or Gamma‐Rays in Radiotherapy Procedures. International Commission on Radiation Units and Measurement; 1976. ICRU Report.<br />International Electrotechnical Commission (IEC). Medical electrical equipment—Dosimeters with ionization chambers as used in radiotherapy. Geneva International Electrotechnical Commission; 2011 IEC 60731 :2011.<br />McEwen M, DeWerd L, Ibbott G, et al. Addendum to the AAPM's TG‐51 protocol for clinical reference dosimetry of high‐energy photon beams. Med Phys. 2014;41(4):041501. doi:10.1118/1.4866223.<br />Morgan AM, Aird EG, Aukett RJ, et al. IPEM guidelines on dosimeter systems for use as transfer instruments between the UK primary dosimetry standards laboratory (NPL) and radiotherapy centres. Phys Med Biol. 2000;45(9):2445‐2457.<br />Blad B, Wendel P, Nilsson P. A simple test device for electrometers. Phys Med Biol. 1998;43(8):2385‐2391.<br />Matsubayashi F, Tsuno H, Matsumoto K, et al. Current generator for precision control of electrometer, precision control system, and calibration method. Japan, 2021: Patent 6989834.<br />Kawashima T, Varnava M, Ozawa S, et al. Measurement and evaluation of electrometer correction factors using a charge generator. J Appl Clin Med Phys. 2023;24(8):e14082. doi:10.1002/acm2.14082.<br />Tsuno H, Matsubayashi F, Sasaki K, Sakai T, Matsumoto K, Takeuchi K. Verification of response uncertainty in electrometers through cross‐comparison with a novel current source: a comparative study with guidelines for electrometers used in radiation therapy dosimeters. Jpn J Med Phys. 2024;44(2):21‐28. doi:10.11323/jjmp.44.2_21.<br />Tsuno H, Matsubayashi F, Sasaki K, Sakai T, Matsumoto K, Takeuchi K. Evaluation on the availability of the electrometer inspection by users using a newly developed current source. Radiol Technol. 2023;79(2):166‐176. doi:10.6009/jjrt.2023‐1216. Japanese.<br />Tsuno H, Sasaki R, Sasaki K, et al. Feasibility study of in‐house second‐channel calibration of dual‐channel electrometers using a battery‐powered current source. J Appl Clin Med Phys Vol. 2026;27(3):e70476.<br />Li G, Xiong J, Sun S, et al. Validation of virtual sensor‐assisted Bayesian inference‐based in‐situ sensor calibration strategy for building HVAC systems. Build Simul. 2023;16(2):185‐203. doi:10.1007/s12273‐022‐0935‐7.<br />Deng H, Wang J, Zhang H, Zhang J, Ma M, Zhong X. An in‐situ self‐calibration method for non‐contact full‐field strain measurement. Measurement. 2020;162:107871. doi:10.1016/j.measurement.2020.107871.<br />Koo J, Yoon S, Kim J. Virtual in situ calibration for operational backup virtual sensors in building energy systems. Energies. 2022;15(4):1394. doi:10.3390/en15041394.<br />Joint Committee for Guides in Metrology (JCGM). Evaluation of Measurement Data—Guide to the Expression of Uncertainty in Measurement (GUM). JCGM 100:2008. JCGM; 2008. doi:10.59161/JCGM100‐2008E.<br />Tsuno H, Sasaki K, Matsubayashi F, et al. New idea for determining the optimal number of measurements in absorbed dose‐to‐water measurement of high‐energy photon beam. Radiat Prot Dosimetry. 2022;199(3):246‐253. doi:10.1093/rpd/ncac262.<br />Tsuno H, Maruyama D, Sasaki K, Matsubayashi F. Optimising the number of measurements for absorbed dose‐to‐water calibration coefficient of ionization chamber by cross‐calibration using high‐energy electron beams. J Radioanal Nucl Chem. 2026;335:4335‐4341. doi:10.1007/s10967‐026‐10921‐0.<br />Castro P, García‐Vicente F, Mínguez C, et al. Study of the uncertainty in the determination of the absorbed dose to water during external beam radiotherapy calibration. J Appl Clin Med Phys. 2008;9(1):70‐86. doi:10.1120/jacmp.v9i1.2676.
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      – SubjectFull: Radiotherapy, Intensity-Modulated methods
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