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Experimental determination of depth‐scaling factors and central axis depth dose for clinical electron beams
Author(s) -
Huq M. Saiful,
Yue N.,
Suntharalingam N.
Publication year - 2001
Publication title -
international journal of cancer
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.475
H-Index - 234
eISSN - 1097-0215
pISSN - 0020-7136
DOI - 10.1002/ijc.1025
Subject(s) - imaging phantom , polystyrene , range (aeronautics) , materials science , ionization chamber , electron , cathode ray , scaling , ionization , nuclear medicine , physics , nuclear physics , medicine , mathematics , composite material , geometry , polymer , ion , quantum mechanics
Depth‐scaling factors ρ eff for clear polystyrene and polymethylmethacrylate (PMMA) phantoms have been determined experimentally as a function of nominal electron‐beam energy in the range 6 to 22 MeV. Values of ρ eff have been calculated from the ratio ρ eff = R wat 50/ R med 50 , where R wat 50and R med 50are the measured depths of 50% ionization in electron solid water and plastic (clear polystyrene and PMMA) phantoms, respectively. Measurements were made using an Attix chamber in an electron solid water phantom, a Holt chamber in a clear polystyrene phantom, and a Markus chamber in a PMMA phantom. The average value of measured ρ poly effwas found to be 0.999 ± 0.009. This is higher than the value of 0.975 recommended by Task Group 25 (TG‐25) of the American Association of Physicists in Medicine (AAPM) by 2.5%. Depending on energy, the maximum differences between the AAPM TG‐25‐recommended and the measured values lie in the range 1% to 3.5%. Similarly, the average value of measured ρ PMMA effwas found to be 1.168 ± 0.023. This is higher than the AAPM TG‐25‐recommended value of 1.115, by 5%. Depending on energy, the maximum differences between the AAPM TG‐25‐recommended and the measured values lie in the range 3% to 8%. Central axis depth dose curves in water were generated for 6, 15, and 20 MeV electron beams from measured depth‐ionization data in PMMA and clear polystyrene phantoms following the recommendations of the AAPM TG‐25 report and using both TG‐25‐recommended and experimentally determined values of depth‐scaling factors ρ eff . For both phantoms, either the TG‐25‐recommended value or the experimentally determined values of ρ eff yielded agreement to within about 2 mm among all depth doses in water at the depths of clinical relevance. © 2001 Wiley‐Liss, Inc.