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Recommendations for measurement of tray and wedge factors for high energy photons
Author(s) -
Sharma S. C.,
Johnson M. W.
Publication year - 1994
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 - 10.1118/1.597392
Subject(s) - wedge (geometry) , tray , dosimetry , optics , monitor unit , linear particle accelerator , calibration , photon , materials science , beam (structure) , physics , computational physics , nuclear medicine , engineering , medicine , mechanical engineering , quantum mechanics
Transmission factors for beam modifiers 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: d max , 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.