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Head‐scatter factors and effective x‐ray source positions in a 25‐MV linear accelerator
Author(s) -
Tatcher Morris,
Bjärngard Bengt
Publication year - 1992
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 - 10.1118/1.596811
Subject(s) - linear particle accelerator , head (geology) , physics , medical imaging , optics , nuclear medicine , medical physics , beam (structure) , medicine , radiology , geology , geomorphology
The behavior of the effective source position and the correction factor associated with the collimator opening (head‐scatter factor) were investigated for the 6‐ and 25‐MV x‐ray beams of a linear accelerator. The primary photon fluence was measured in air for square field sizes from 5×5 cm to 40×40 cm at distances from the nominal source of 80 to 140 cm, for open and wedged fields (wedge angle 60 deg). An inverse‐square analysis shows that, for open fields, the effective source position of the accelerator is about the same (approximately 1 cm downstream) at 6 and 25 MV, for all field sizes. For the wedged fields, the effective source position depends on field size and ranges from about 2 to 4 cm. The head‐scatter correction factors for given collimator settings were found to be essentially independent of distance at both energies.