title: Recommendations for measurement of tray and wedge factors for high energy photons.
abstract: Transmission factors for beam modifers such as wedges and blocking trays in dosimetry calculations are very common, but various methods have been used in measuring these factors. A systematic study to measure these factors as a function of field size and point of measurement was carried out. The beam modifiers were a blocking tray and the standard wedges supplied with a cobalt-60 unit and a medical electron accelerator (6- and 18-MV x rays). Several points of measurement were selected, using several depths: dmax, TG-21 calibration depth, 10 cm (wedge angle defining depth, ICRU), 15 cm and in-air (miniphantom), and various field sizes. The results show a small field size dependence in these transmission factors with more dependence found in the point of measurement.
authors.affiliation: Department of Radiation Oncology, E. W. Sparrow Hospital, Lansing, Michigan 48909.
authors.forename: S C
authors.initials: SC
authors.lastname: Sharma
authors.forename: M W
authors.initials: MW
authors.lastname: Johnson
mesh_terms: D000388:Air; D055592:Biophysical Phenomena; D001703:Biophysics; D005720:Gamma Rays; D006801:Humans; D008961:Models, Structural; D010315:Particle Accelerators; D017785:Photons; D011137:Polystyrenes; D011835:Radiation Protection; D011867:Radioisotope Teletherapy / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D011882:Radiotherapy, High-Energy; D013679:Technology, Radiologic
chemical_list: D011137:Polystyrenes