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Revision of tissue‐maximum ratio and scatter‐maximum ratio concepts for cobalt 60 and higher energy x‐ray beams
Author(s) -
Khan Faiz M.,
Sewchand Wilfred,
Lee Joseph,
Williamson Jeffrey F.
Publication year - 1980
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 - 10.1118/1.594648
Subject(s) - imaging phantom , collimator , x ray , optics , physics , range (aeronautics) , energy (signal processing) , dosimetry , nuclear medicine , materials science , medicine , quantum mechanics , composite material
The concept of tissue‐maximum ratios (TMR) as a basis of dose computations has posed problems when applied to the whole range of clinically used megavoltage beams. Another problem is the definition of scatter‐maximum ratio (SMR) which assumes a value of zero at the depth of maximum dose. This paper describes new methods of measuring collimator and phantom scatter correction factors. The definitions of TMR and SMR are modified in order to compute phantom scatter at any depth, including depth of maximum dose. The revised concept is basic and general enough that it can be applied to x‐ray beams of any energy, fields of any shape and isocentric as well as non‐isocentric modes of treatment.