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Medical Physics / Volume 7 / Issue 3

Med. Phys. 7, 230 (1980); http://dx.doi.org/10.1118/1.594648 (8 pages)

Revision of tissue‐maximum ratio and scatter‐maximum ratio concepts for cobalt 60 and higher energy x‐ray beams

Faiz M. Khan, Wilfred Sewchand, Joseph Lee, and Jeffrey F. Williamson

Department of Therapeutic Radiology, Box 494 University Hospitals, 420 Delaware Street S. E., University of Minnesota, Minneapolis, Minnesota 55455

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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.
Digital Object Identifier
http://dx.doi.org/10.1118/1.594648

KEYWORDS and PACS

Keywords

COLLIMATORS, X−RAY DOSIMETRY, COBALT 60, RADIOTHERAPY, CORRECTIONS, DEPTH DOSE DISTRIBUTIONS

PACS

PUBLICATION DATA

ISSN

0094-2405 (print)  

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Medical Physics is an official science journal of the AAPM and of the COMP/CCPM/IOMP
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Departments of Radiology, Radiation Oncology, Biophysics, Community and Public Health, Medical College of Wisconsin
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