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The US radiation dosimetry standards for Co 60 therapy level beams, and the transfer to the AAPM accredited dosimetry calibration laboratories
Author(s) -
Minniti R.,
ChenMayer H.,
Seltzer S. M.,
Huq M. Saiful,
Bryson L.,
Slowey T.,
Micka J. A.,
DeWerd L. A.,
Wells N.,
Hanson W. F.,
Ibbott G. S.
Publication year - 2006
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2184442
Subject(s) - kerma , nist , dosimetry , primary standard , calibration , medical physics , nuclear engineering , nuclear medicine , physics , medicine , computer science , engineering , quantum mechanics , natural language processing
This work reports the transfer of the primary standard for air kerma from the National Institute of Standards and Technology (NIST) to the secondary laboratories accredited by the American Association of Physics in Medicine (AAPM). This transfer, performed in August of 2003, was motivated by the recent revision of the NIST air‐kerma standards for Co60 gamma‐ray beams implemented on July 1, 2003. The revision involved a complete recharacterization of the two NIST therapy‐level Co60 gamma‐ray beam facilities, resulting in new values for the air‐kerma rates disseminated by the NIST. Some of the experimental aspects of the determination of the new air‐kerma rates are briefly summarized here; the theoretical aspects have been described in detail by Seltzer and Bergstrom [“Changes in the U.S. primary standards for the air‐kerma from gamma‐ray beams,” J. Res. Natl. Inst. Stand. Technol. 108, 359–381 (2003)]. The standard was transferred to reference‐class chambers submitted by each of the AAPM Accredited Dosimetry Calibration Laboratories (ADCLs). These secondary‐standard instruments were then used to characterize the Co60 gamma‐ray beams at the ADCLs. The values of the response (calibration coefficient) of the ADCL secondary‐standard ionization chambers are reported and compared to values obtained prior to the change in the NIST air‐kerma standards announced on July 1, 2003. The relative change is about 1.1% for all of these chambers, and this value agrees well with the expected change in chambers calibrated at the NIST or at any secondary‐standard laboratory traceable to the new NIST standard.