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Determination of electron beam mean incident energy from d 5 0 (ionization) values
Author(s) -
Ten Haken Randall K.,
Fraass Benedick A.
Publication year - 1987
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 - 10.1118/1.596115
Subject(s) - ionization , dosimetry , ionization chamber , percentage depth dose curve , beam divergence , range (aeronautics) , imaging phantom , beam (structure) , detector , electron , atomic physics , diode , optics , physics , materials science , computational physics , laser beam quality , nuclear medicine , nuclear physics , ion , optoelectronics , medicine , laser , composite material , quantum mechanics , laser beams
Depth‐ionization measurements have been obtained with an air‐filled Nordic Association of Clinical Physicists (NACP) design parallel‐plate ionization chamber in a water phantom for ten foil‐scattered electron beams from two different machines with nominal energies between 6 and 20 MeV and field sizes from 6×6 to 25×25 cm 2 . Depths of 50% ionization and practical range have been determined from least‐squares fits to both the raw data and values corrected to parallel‐beam geometry using measured virtual source distances. Depths of 50% dose have also been obtained from fits to divergence‐corrected depth‐dose measurments performed under identical conditions using, a p ‐type silicon diode detector. Utilizing accepted conversion factors between mean incident energy ( E ̄ 0 ) and depth of 50% dose for parallel incident beams, and taking advantage of the fact that p ‐type silicon diode detector readings are nearly directly indicative of relative dose, conversion factors between E ̄ 0 and depth of 50% ionization for divergence‐corrected and raw, uncorrected finite source‐surface distance depth‐ionization data are empirically determined. Those values, obtained using the results of both ETRAN and EGS4 dose calculations as base lines, are compared to values currently recommended for use in clinical dosimetry.