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A block design for split‐field tests of accelerator alignment
Author(s) -
Ford Eric C.,
Lutz Wendell R.
Publication year - 2004
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 - 10.1118/1.1773621
Subject(s) - collimator , linear particle accelerator , optics , block (permutation group theory) , beam (structure) , rotation (mathematics) , field (mathematics) , enhanced data rates for gsm evolution , collimated light , quality assurance , tray , computer science , physics , engineering , geometry , mathematics , telecommunications , laser , operations management , external quality assessment , pure mathematics , mechanical engineering
We present a block design that facilitates split‐field tests, a technique frequently employed to assess several potential misalignments in linear accelerators. Two tests are possible with this device using: (1) opposed collimator angles and (2) opposed gantry angles. The first test is sensitive to jaw symmetry only. In the second test, the alignment of one field edge indicates gantry sag, while the other field edge is sensitive to the combined effects of jaw asymmetry, misalignment of the beam spot, and misalignment of the gantry and collimator rotation axes. The block arrangement consists of a pattern of three polygons cast in lead or Cerrobend. The assembly mounts in the accessory tray of the accelerator and allows all necessary exposures to be taken in a single room entry. Any field size up to 24 cm can be tested with the assembly constructed here. A simultaneous test of light field‐radiation field coincidence can also be accommodated. Exposed films with a prototype device show that offsets of ±1 mm are readily visible. The block design facilitates the required measurements for split‐field tests and makes this a practical technique for routine quality assurance on a linear accelerator.