Calibration of Therapy-level Dosimeters in Japan by Association for Nuclear Technology in Medicine (ANTM)

Abstract

In 2004, the calibration system of therapy-level dosimeter sensitivity has been reformed in Japan. An organization of new dosimeter calibration system by Association for Nuclear Technology in Medicine (ANTM) was launched from April, 2004 instead of the old system which was operated by Japan Radiological Society (JRS). Since then, about 5 years have passed, and the calibration work has been carried out favorably in general. It is thought that the transfer of dosimeter calibration system was performed smoothly.

The reference dosimeters of ANTM are calibrated by the comparison with the standard dosimeter owned by National Institute of Advanced Industrial Science and Technology (AIST) that is the PSDL of radiation dose in Japan. ANTM acts as a SSDL practically, i.e. ANTM calibrates dosimeters used in clinical institutions in whole Japan. As the old system by JRS had several calibration steps, the reduction of uncertainties accompanying with standard transfer steps would be expected in new system by ANTM.

The total of the dosimeter calibrated by ANTM from April/’04 to March/’09 was 3,407 and the total of ionization chamber was 7,746 that are divided into two groups of 4,900 cylindrical type (63%) and 2,846 shallow type (37%). The average of ratios of calibration factor to previous one was almost 1.000 and the standard deviation of ratios was almost 0.006 every year. Therefore, the variation of calibration factors delivered by ANTM are so small that the calibration system by ANTM works in stable and traceability of therapy level dosimeter in Japan is maintained effectively and in high level.