@misc{oai:repo.qst.go.jp:00071019,
 author = {Fukumura, Akifumi and Mizuno, Hideyuki and Fukahori, Mai and Sakata, Suho and 福村 明史 and 水野 秀之 and 深堀 麻衣 and 佐方 周防},
 month = {Dec},
 note = {DEVELOPMENT OF 60Co GAMMA-RAY STANDARD FIELD
 FOR THERAPY-LEVEL DOSIMETER CALIBRATION 
IN TERMS OF ABSORBED DOSE TO WATER
\nAkifumi Fukumura, Hideyuki Mizuno, Mai Fukahori, Suoh Sakata
National Institute of Radiological Sciences (NIRS),Chiba, Japan
\n
A primary standard for the absorbed dose rate to water in a 60Co gamma-ray field established at National Metrology Institute of Japan (NMIJ) as a primary standard dosimetry laboratory (PSDL) in 2011. Then, a 60Co gamma-ray standard field for therapy-level dosimeter calibration in terms of absorbed dose to water has been developed at National Institute of Radiological Sciences (NIRS) as a secondary standard dosimetry laboratory (SSDL). The field was designed in accordance with IAEA TRS 398.
\nThe result of IAEA/WHO TLD SSDL audit with the new field at NIRS demonstrated the good agreement between NIRS stated absorbed dose to water and IAEA TLD measurements within the measurement uncertainty. According to IAEA TECDOC-1585, the relative expanded uncertainty on the calibration factor for therapy-level therapy-level dosimeter in terms of absorbed dose to water (ND,w) with the new field was estimated to 1.1 % (k=2), which is corresponding to an international level such as 1.4% at ADSL in the US and approximately one third of it determined in the air kerma standard field previously existing at NIRS. 
\nThe new field has been used for determination of ND,w for radiotherapy facilities in Japan since the beginning of October in 2012. At the same time Japan Society of Medical Physics (JSMP) updated its code of practice for dosimetry in external radiotherapy. The dissemination of traceability of calibration factor determined in the new field is expected to diminish the uncertainty of dose delivered to patients significantly., 12th Asia-Oceania Congress of Medical Physics (12th AOCMP)},
 title = {DEVELOPMENT OF 60Co GAMMA-RAY STANDARD FIELD FOR THERAPY-LEVEL DOSIMETER CALIBRATION IN TERMS OF ABSORBED DOSE TO WATER},
 year = {2012}
}