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Wedge factor dependence on depth and field size for various beam energies using symmetric and half‐collimated asymmetric jaw settings
Author(s) -
NiroomandRad Azam,
Haleem Mahmoud,
Rodgers James,
Obcemea Ceferino
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 - 10.1118/1.596800
Subject(s) - collimated light , wedge (geometry) , optics , physics , beam (structure) , field size , field (mathematics) , dosimetry , materials science , mathematics , nuclear medicine , laser , medicine , pure mathematics
The depth‐ and field‐size dependence of the in‐phantom wedge factor have been determined for a Cobalt‐60 (Co‐60) teletherapy unit and four medical linear accelerators with 4‐, 6‐, 10‐, and 18‐MV x‐ray beams containing 15°–60° (nominal) lead, brass, and steel wedge filters. Measurements were made with ionization chambers in solid water or water with a source‐skin distance of 80 or 100 cm. Field sizes varied from 4×4 cm up to a maximum allowable size for each wedge filter. Measurements were performed for symmetric and half‐collimated asymmetric fields at depth of maximum dose, 5‐ and 10‐cm depths. For half‐collimated fields, wedge factor reference points were located at a fixed off‐axis distance from the collimator's rotational axis. These systematic measurements on wedges indicate that the wedge factor dependence on depth and field size is a function of beam energy as well as the design of the treatment head and wedge filters. Significance of the results reported herein are discussed for the most commonly used treatment depths and field sizes with various beam energies and wedge filters.