Examining electrometer performance checks with direct-current generator in a clinic: Assessment of generated charges and implementation of electrometer checks.
J Appl Clin Med Phys
; 22(7): 306-312, 2021 Jul.
Article
em En
| MEDLINE
| ID: mdl-34085364
ABSTRACT
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 607312011, ≤0.5% (reference-class dosimeter)], and calibration frequency [according to Muir et al. (J Appl Clin Med Phys. 2017; 18182-190), 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; 432385-2391) 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 607312011 were checked for repeatability at a current of ±20 pA or a minimum effective indicated value meeting IEC 607312011, 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.Palavras-chave
Texto completo:
1
Base de dados:
MEDLINE
Assunto principal:
Radiometria
/
Eletrônica
Limite:
Humans
Idioma:
En
Ano de publicação:
2021
Tipo de documento:
Article