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Dose measurements in the build‐up region for Cobalt‐60 therapy units
Author(s) -
Leung Philip M. K.,
Sontag Marc R.,
Maharaj Harrideo,
Chenery Stafford
Publication year - 1976
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 - 10.1118/1.594220
Subject(s) - collimator , dosimetry , cobalt 60 , nuclear medicine , materials science , optics , cobalt , physics , medicine , nuclear physics , irradiation , metallurgy
The dose in the build‐up region for four different Cobalt‐60 therapy units was measured. It was found that, for large collimator openings and relatively short SSDs, a new dose peak occurs at a depth very much smaller than 0.5 cm. The dose at this peak is a function of collimator openings and SSDs and, in some extreme case, could be 15% or more higher than the dose at the conventional peak dose of 0.5 cm. The new dose peak is probably due to electrons produced in the source capsule and the part of the collimator close to the source; it can be almost eliminated by a filter placed just below the collimator.