(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: In Japan, the separated calibration of ionization chamber has been began since 2018.In order to perform separated calibration, it is important to inspect the electrometer. However, there are inspection contents that require the use of special equipment, and it is difficult for users to those contents. The aim of this study is to establish a simple quality assurance (QA) method for electrometer without special equipment. Particularly the repeatability described in the guideline for the separated calibration was studied in this study.
Methods: We used Vero4DRT(Mitubishi) as a linear accelerator, PC Electrometer(Sun Nuclear) and UNIDOS webline(PTW) as the electrometers, respectively. We installed UNIDOS webline as a monitoring electrometer and PC Electrometer as a field electrometer. Then the environment was switched. 100 MU was measured 5 times, 300 MU and 500 MU at once were measured three times, respectively. The value of field electrometer was divided by the value of monitor electrometer, for purpose of reducing uncertainty of dose variation. The value from 100 MU was tripled and compared with the value of 300 MU. Similarly, the value obtained from 100 MU was multiplied by 5 and compared with the value obtained from 500 MU.
Results: The coefficient of variation at 100 MU only was 0.0418. The values of 300 MU and 500 MU at once were lager than 100 MU x 3 and 100 MU x 5, respectively. These results were satisfied for repeatability of QA guideline for electrometer.
Conclusion: We proposed a simplified method for QA of electrometer without current source. However, it is not possible to make sure the influence of either the zero drift during the measurement or the setting the electrometer in the treatment room.
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