Standard dosimetry of 125I seeds against prostate cancer

We have established the standard seed assay method using the well-type ionization chambers, after two years experiences of measurements. It is clear that the single seed measurement whose dose sensitivity is traceable to the standard is the basic method. Currently NIST traceable well-type ionization chamber is the only the system to be used for the seed assay. In order to establish Japanese national standard for the air kerma strength measurement and also to establish the traceability chain of calibration, we started to establish national standard ionization chamber at Japanese primary dosimetry laboratory (AIST).