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Lateral electron equilibrium and electron contamination in measurements of head‐scatter factors using miniphantoms and brass caps
Author(s) -
Li X. Allen,
Soubra M.,
Szanto J.,
Gerig L. H.
Publication year - 1995
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 - 10.1118/1.597508
Subject(s) - electron , cathode ray , monte carlo method , atomic physics , electron scattering , contamination , photon , brass , materials science , yield (engineering) , physics , optics , nuclear physics , copper , metallurgy , biology , ecology , statistics , mathematics
The head‐scatter factor ( S h ) can be measured with a narrow miniphantom or a metal cap provided it is completely covered by the photon beam and its lateral size is thick enough to prevent electron contamination contributions. The effects of lateral electron equilibrium (LEE) and electron contamination on the S h values were studied. The EGS4 Monte Carlo technique was used to calculate the minimum beam radii ( r LEE ) required to achieve complete LEE for photon beams ranging from 60 Co to 24 MV. The measurement shows that the error introduced to the S h value due to lateral electron disequilibrium is negligible. The radii of the miniphantoms or the sidewall thicknesses of the caps can be reduced below r LEE provided they are thick enough to prevent the effect of electron contamination.