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The effect of differences in data base on the determination of absorbed dose in high‐energy photon beams using the American Association of Physicists in Medicine protocol
Author(s) -
Mijnheer B. J.,
Chin L. M.
Publication year - 1989
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 - 10.1118/1.596398
Subject(s) - nist , stopping power , calibration , absorbed dose , dosimetry , nuclear medicine , photon , protocol (science) , physics , computational physics , statistics , mathematics , computer science , medicine , optics , detector , alternative medicine , pathology , natural language processing
Exposure rates were adjusted at the National Institute of Standards and Technology (NIST) on January 1, 1986 to take into account more recent values for some physical parameters, mainly in electron stopping power ratios. Exposure calibration factors for 6 0 Co gamma rays N X will therefore be lowered by 1.1%. Consequently, absorbed dose determinations in high‐energy photon beams will be reduced by the same amount if the values for these physical parameters remain unchanged in the American Association of Physicists in Medicine (AAPM) protocol. If the same data base as used at NIST is applied in the AAPM protocol, then N gas / N X values, water–air stopping power ratios, and P wall values will be different. The overall change in absorbed dose determinations using a consistent set of data will be a reduction of 0.8% for 6 0 Co gamma rays and 1.5% for a 20‐MV x‐ray beam compared to the values before January 1, 1986. Since the net effect is small when different sets of data are applied, the new NIST exposure calibration factors may be used in combination with the AAPM protocol without significant error.