Premium
Output factor constituents of a high‐energy photon beam
Author(s) -
Luxton Gary,
Astrahan Melvin A.
Publication year - 1988
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 - 10.1118/1.596300
Subject(s) - collimator , imaging phantom , optics , linear particle accelerator , physics , aperture (computer memory) , beam (structure) , photon , monitor unit , backscatter (email) , flattening , dosimetry , field size , nuclear medicine , computer science , medicine , telecommunications , astronomy , acoustics , wireless
Measurements designed to separate primary and various scatter components of central axis dose of the highest energy photon beam of the CGR Saturne 25 linear accelerator are described. This beam has an unusually large output variation with field size. The measurements are performed both in air and in a water phantom, with and without an aperture external to the collimator system. Results are presented in the form of relative output factors for different field sizes due to (i) flattening filter scatter, (ii) water phantom scatter, (iii) collimator backscatter into the monitor chamber, and (iv) collimator forward scatter onto the central axis. It is found that the flattening filter is the single largest scatter component, but that each of the other factors is significant in determining the output dose per monitor unit as a function of field size.