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Compensating filters for high energy x rays
Author(s) -
Boyer Arthur L.
Publication year - 1982
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 - 10.1118/1.595225
Subject(s) - flatness (cosmology) , attenuation , attenuation coefficient , gamma ray , optics , filter (signal processing) , materials science , energy (signal processing) , cobalt 60 , range (aeronautics) , physics , computer science , irradiation , nuclear physics , cosmology , quantum mechanics , composite material , computer vision
In order to produce individualized compensating filters for use with high energy x rays, a study was undertaken to study lead as a filter material using 10‐MV x rays. As was expected, it was found that lead filters could be constructed for 10‐MV x rays by extending concepts developed for cobalt‐60 gamma rays. A quantity called the “effective attenuation coefficient” (μ eff ) was determined for a range of field sizes, initial depths in water, and lead thicknesses and for 100‐cm SSD and 150‐cm SSD treatment techniques. Slight variations of μ eff with field area and filter thickness were discernable. However, a single value of this parameter could reproduce the original depth of missing tissue data with an rms error of 2 mm. Tests were then performed on filters whose shapes were calculated using the effective attenuation coefficient. Compensating filters restored the flatness of 10‐MV x‐ray beams to better than 5%, which was better than comparable filters using cobalt‐60 gamma rays. The technique is presented as generally reliable for constructing compensating filters for use with high energy linear accelerators.