Open AccessDetermination of field size‐dependent wedge factors from a few selected measurements
Author(s) -
Popple Richard A.,
Brezovich Ivan A.,
Duan Jun,
Shen Sui,
Pareek Prem N.,
Ye SungJoon
Publication year - 2005
Publication title -
journal of applied clinical medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.83
H-Index - 48
ISSN - 1526-9914
DOI - 10.1120/jacmp.v6i1.2063
Subject(s) - wedge (geometry) , linear particle accelerator , monitor unit , field size , field (mathematics) , square (algebra) , range (aeronautics) , mathematics , physics , optics , geometry , materials science , beam (structure) , nuclear medicine , medicine , pure mathematics , composite material
Some modern treatment‐planning systems (TPSs) provide for input of wedge factor (WF) tables covering the entire range of square and elongated fields available on the LINAC. Depending on the field size increment chosen and the number of available wedge orientations, one may have to take more than 100 measurements per wedge and photon energy to commission the TPS. To expedite TPS commissioning while maintaining high accuracy, we demonstrate a simple method that requires only a few measurements per wedge, from which the remaining wedge factors can be found through linear interpolation based on field area. For the externally mounted wedges of two common LINACs, we have shown that WFs are proportional to field area and are nearly independent of field elongation and wedge orientation. Wedge factors computed from five to seven measurements comprised of square fields and a single, large rectangular field agreed with direct measurements throughout the entire range of achievable field dimensions within 0.6% at 6 MV and within 1% at 15 MV. Making the same set of measurements and using the equivalent square method to find WFs at other field sizes leads to errors up to 2%. Measuring the WF for a 10 × 10cm 2field and applying the same value to all field sizes can lead to errors of up to 10% at both 6 MV and 15 MV. PACS numbers: 87.53.Bn, 87.53.Mr