Examining electrometer performance checks with direct-current generator in a clinic: Assessment of generated charges and implementation of electrometer checks
Autor: | M. Shimizu, Hiroki Shioura, Eiji Kidoya, Naoki Kinoshita, Hirohiko Kimura, Hiroshi Oguchi |
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Rok vydání: | 2021 |
Předmět: |
Electric generator
Electrometer 030218 nuclear medicine & medical imaging law.invention Generator (circuit theory) 03 medical and health sciences 0302 clinical medicine law Calibration Humans Radiology Nuclear Medicine and imaging clinical electrometer check repeatability Radiometry Instrumentation Physics Radiation Dosimeter business.industry Direct current Detector Electrical engineering nonlinearity Repeatability electrometer equipped with direct‐current generator Radiation Measurements 030220 oncology & carcinogenesis Electronics business |
Zdroj: | Journal of Applied Clinical Medical Physics |
ISSN: | 1526-9914 |
Popis: | Purpose Medical physicists use a suitable detector connected to an electrometer to measure radiotherapy beams. Each detector and electrometer has a lifetime (due to physical deterioration of detector components and electrical characteristic deterioration in electronic electrometer components), long‐term stability [according to IEC 60731:2011, ≤0.5% (reference‐class dosimeter)], and calibration frequency [according to Muir et al. (J Appl Clin Med Phys. 2017; 18:182‐190), generally 2 years]; thus, physicists should check the electrometer and detector separately. However, to the best of our knowledge, only one study (Blad et al., Phys Med Biol. 1998; 43:2385–2391) has reported checking the electrometer independently from the detector. The present study conducts performance checks on electrometers separately from the detector in clinical settings, using an electrometer equipped with a direct current (DC) generator (EMF 521R) capable of injecting DC (effective range: ±20 pA to ±20 nA) into itself or another electrometer. Methods First, to check the nonlinearity of the generated currents from ±20 pA to ±20 nA, charges generated from the DC generator were measured with the EMF 521R electrometer. Next, six reference‐class electrometers classified according to IEC 60731:2011 were checked for repeatability at a current of ±20 pA or a minimum effective indicated value meeting IEC 60731:2011, as well as for nonlinearity within the current range from ±20 pA to ±20 nA. Results The nonlinearities for the measured currents were less than ±0.05%. The repeatability for the six electrometers was < 0.1%. While the nonlinearity of one electrometer reached up to 0.22% at a current of –20 pA, all six electrometers displayed nonlinearities of less than ±0.1% at currents of ±100 pA or higher. Conclusions This work suggests that it is possible to check the nonlinearity and repeatability of clinical electrometers with DCs above the ±30 pA level using a DC generator in a clinic. |
Databáze: | OpenAIRE |
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