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An equivalent square field formula for determining head scatter factors of rectangular fields
Author(s) -
Kim Siyong,
Zhu Timothy C.,
Palta Jatinder R.
Publication year - 1997
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 - 10.1118/1.597963
Subject(s) - square (algebra) , collimator , field (mathematics) , head (geology) , range (aeronautics) , mathematics , aperture (computer memory) , linear particle accelerator , mathematical analysis , geometry , optics , physics , beam (structure) , materials science , geomorphology , acoustics , pure mathematics , composite material , geology
A simple formula is derived for the calculation of an equivalent square field that gives the same head scatter factor as a given rectangular field. This formula is based strictly on the configuration of a medical linear accelerator treatment head. The geometric parameters used are the distances between the target and the top of each field‐defining aperture. The formula accounts for both the effect of field elongation and the collimator exchange effect. This method predicts the output to within 1% accuracy for both open and wedged fields and does not require any new measured data other than the field size dependence of head scatter for a range of square field sizes. Interestingly, the formula we derived has the same format as the formula that was empirically obtained by Vadash and Bjärngard [Med. Phys. 20 , 733–734 (1993)].