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Po‐Poster ‐ 10: Influence of varying SSD on the penumbra and the mean square scattering angle for electron beams
Author(s) -
Hodefi D
Publication year - 2005
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 - 10.1118/1.2030989
Subject(s) - penumbra , cathode ray , beam (structure) , electron , optics , scattering , range (aeronautics) , atomic physics , materials science , electron scattering , physics , nuclear physics , medicine , ischemia , cardiology , composite material
The objective of this study was to quantify how varying source to surface distance (SSD) for electron beam therapy affects the width of the penumbra at the surface of the patient and to determine the influence of the SSD on the mean square scattering angle at the base of the electron applicator, 〈θ 2 〉(0), for use in electron beam treatment planning. Penumbra values were extracted from profiles measured at the surface of a water phantom for SSDs spanning 103–116 cm for numerous combinations of beam energy and electron applicator. 〈θ 2 〉(0) was derived from the measured penumbra values. The width of the penumbra was shown to climb in a linear fashion with increasing SSD over the range of values investigated. It was also observed that the size of the electron cone exerted considerably more influence on the penumbra for a given SSD for lower beam energies than for higher beam energies. In the case of lower beam energies, the penumbra width for a given SSD rose in a very significant way with increasing applicator size. 〈θ 2 〉(0) demonstrated a decreasing trend as SSD was increased. This decline was more drastic for lower beam energies. For higher beam energies, 〈θ 2 〉(0) values tended to be quite similar, despite varying SSD.