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Improving the buildup and depth‐dose characteristics of high energy photon beams by using electron filters
Author(s) -
Ling C. Clifton,
Biggs Peter J.
Publication year - 1979
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 - 10.1118/1.594585
Subject(s) - foil method , electron , linear particle accelerator , beam (structure) , photon , materials science , cathode ray , field (mathematics) , particle accelerator , dosimetry , magnet , atomic physics , optics , physics , nuclear physics , nuclear medicine , medicine , mathematics , quantum mechanics , pure mathematics , composite material
The attributes of high energy photon beams, i.e., low surface dose, large d max and improved %DD, are compromised with increase in field size. This is due to the relative increase with field size of the electron component in the beam, as shown by recent experiments done here using a sweeping magnet. The present study shows that the advantages can be partially regained with the use of foils to remove electrons. Various thicknesses of Al, Cu, Sn, and Pb were placed in a 25‐MV linac x‐ray beam at several sites in the treatment head. Buildup curves were measured with a “pancake” chamber for various SSD and field sizes. The magnitude of improvement achieved is dependent upon field size, SSD, the atomic number of the foil material, and foil thickness. Pb foil (0.55 g cm −2 ) provided the best overall improvement. Surface dose reduction of 10%–20% can be achieved along with significant increase in d max and %DD. These findings suggest a new design feature for the next generation of high energy linacs.