[Outline of standard dosimetry of absorbed dose to water in external beam radiotherapy].

In this report, history of the dose standard system, calibration of ionization chamber and standard dosimetry protocol to assure dose traceability was interpreted. The water absorbed dose standard is newly established in Japan and calibration service and dosimetry protocol based on the water absorbed dose has been provided. A lot of uncertainties exist in current complicated radiation therapy. However, uncertainty of dose delivery will be reduced and further progress of quality assurance is expected by shift to the absorbed dose calibration system in radiation therapy field.