Annual change in calibration constant of ionization chamber used in diagnostic radiology

: Committee on Radiological Protection of Japan Radiological Society (JRS) is making a database on patient doses for typical radiographies for introducing the guidance levels in Japan. The Committee reported necessity of a protocol on dosimetry in diagnostic radiology for introducing the guidance levels. Although a protocol on dosimetry in radiation therapy is established, there is no protocol on dosimetry in diagnostic radiology in Japan. Then, as a first step to establish a protocol on dosimetry in diagnostic radiology, annual changes in a calibration constant of an ionization chamber as a practical standard dosimeter has been investigated for 4 years. Changes in calibration constants for 4 years are within 2% for X-rays with effective energies than 32 keV. From these results, practical frequencies of calibrations for practical standard dosimeters are discussed for maintain of their precision. If an accuracy of practical standard dosimeters is 5% for diagnostic radiology, frequencies of their calibrations may be once in a year or two years.