Electron contamination in 6 0 Co gamma‐ray beams
Author(s) -
Attix F. H.,
Lopez F.,
Owolabi S.,
Paliwal B. R.
Publication year - 1983
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 - 10.1118/1.595305
Subject(s) - physics , gamma ray , electron , cobalt 60 , radiochemistry , nuclear physics , atomic physics , chemistry , irradiation
All radiotherapy photon beams are accompanied to some extent by secondary electrons which originate in interactions with source hardware, collimator, shadow tray, and/or the air through which the beam passes. Skin sparing, the shape of the dose buildup curve, and the depth of the dose maximum are all influenced by this electron “contamination.” The present study of a 6 0 Co source employs a flat ion chamber to measure dose buildup curves in polystyrene at source distances of 72 to 200 cm, with an open beam or a filter of Lucite, Cu, Pb‐loaded acrylic, or Ba‐ or Pb‐loaded nonbrowning glass placed 57 cm from the source, using 5×5, 20×20, and 35×35‐cm 2 beams as defined at 80 cm SSD. The effect of electron generation in the air was studied by placing a He‐gas‐filled plastic bag in the beam. A value of about 12% is estimated for the lowest relative dose obtainable with a polystyrene phantom in a “clear” 6 0 Co γ‐ray beam of 1‐cm diameter.