Feasibility study of in‐house second‐channel calibration of dual‐channel electrometers using a battery‐powered current source

Abstract Background An ionization chamber and electrometer allow measurement of the absorbed dose to water. A sensitivity comparison between electrometers is essential for quality control, and an efficient method is available to accurately measure the electrometer sensitivity coefficient without using a linear accelerator (linac). Although dual‐ circuit electrometers are becoming increasingly common, no calculation method for the sensitivity coefficient of their second‐circuit is available. Hence, we propose a method for calculating this sensitivity coefficient using the first‐circuit as the reference and evaluate its accuracy. Methods Using the first‐circuit of a RAMTEC pro electrometer as a reference, the RAMTEC duo and SuperMAX electrometers were connected as test units to the simple yet accurate Japanese‐patented SCG002 current source powered by a dry cell battery. Sensitivity ratio r elec ​ was calculated from the average of three charge measurements using RAMTEC Pro. This ratio was multiplied by the calibration coefficient of the first‐ circuit to obtain the sensitivity coefficient of the second‐circuit. The accuracy was obtained from the relative error of each electrometer based on the calibration coefficient ( k elec ) provided by a standards laboratory. Results The sensitivity coefficient of the second‐circuit of RAMTEC pro was 1.0004 (relative error, +0.030%). For RAMTEC duo, the first‐ and second‐circuit coefficients were 1.0014 and 1.0013, respectively (relative errors, +0.080% and +0.070%). For SuperMAX, the coefficients were 0.9986 and 0.9983 (relative errors, 0.0% and –0.050%) for the first and second circuits, respectively. Thus, the proposed method provided accurate measurements. Conclusion We accurately determine the sensitivity coefficient of the second‐circuit in a dual‐circuit electrometer using the first‐circuit of the same or another electrometer as the reference. If the electrometer performance is verified, the coefficient k elec of the first‐circuit is likely applicable to the second‐circuit. This method may reduce the costs associated with electrometer calibration in clinical settings.