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Generalized monitor unit calculation for the Varian enhanced dynamic wedge field
Author(s) -
Liu Chihray,
Kim Siyong,
Kahler Darren L.,
Palta Jatinder R.
Publication year - 2003
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 - 10.1118/1.1586269
Subject(s) - wedge (geometry) , monitor unit , field (mathematics) , position (finance) , physics , geodetic datum , mathematics , mathematical analysis , geometry , geodesy , geology , nuclear medicine , medicine , finance , pure mathematics , economics
The generalized monitor unit (MU) calculation equation for the Varian enhanced dynamic wedge (EDW) is derived. The assumption of this MU calculation method is that the wedge factor of the EDW at the center of the field is a function of field size, the position of the center of the field in the wedge direction, and the final position of the moving jaw. The wedge factors at the center of the field in both symmetric and asymmetric fields are examined. The difference between calculated and measured wedge factors is within 1.0%. The method developed here is easy to implement. The only datum required in addition to the standard set of conventional physical wedge implementation data is the off‐axis output factor for the open field in the reference condition. The off‐center point calculation is also examined. For the off‐center point calculation, the dose profile in the wedge direction for the largest EDW field is used to obtain the relative off‐center ratio in any smaller wedge field. The accuracy of the off‐center point calculation decreases when the point of calculation is too close to the field edge.