title: Wedge factor dependence on depth and field size for various beam energies using symmetric and half-collimated asymmetric jaw settings.
abstract: 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 degrees-60 degrees (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 x 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.
authors.affiliation: Department of Radiation Medicine, Georgetown University Medical Center, Washington, DC 20007-2197.
authors.forename: A
authors.initials: A
authors.lastname: Niroomand-Rad
authors.forename: M
authors.initials: M
authors.lastname: Haleem
authors.forename: J
authors.initials: J
authors.lastname: Rodgers
authors.forename: C
authors.initials: C
authors.lastname: Obcemea
mesh_terms: D003037:Cobalt Radioisotopes; D006801:Humans; D010315:Particle Accelerators; D011867:Radioisotope Teletherapy / Q000295:instrumentation*; D011874:Radiometry / Q000295:instrumentation; D011882:Radiotherapy, High-Energy
chemical_list: D003037:Cobalt Radioisotopes