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On the selection of stopping‐power and mass energy‐absorption coefficient ratios for high‐energy x‐ray dosimetry
Author(s) -
Cunningham John R.,
Schulz Robert J.
Publication year - 1984
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 - 10.1118/1.595643
Subject(s) - stopping power , dosimetry , absorption (acoustics) , attenuation coefficient , materials science , nuclear physics , physics , atomic physics , computational physics , nuclear medicine , optics , medicine , detector
A method for the selection of average stopping‐power (L̄/ρ) air medand energy‐ absorption coefficient (μ̄ en/ρ) air medratios has been developed. The quality of the x‐ray beam is characterized by the ratio of ionization chamber readings at depths of 20 and 10 cm in water (TMR) 10 20 . For convenience, a relationship is established between experimental (TMR) 10 20and the nominal accelerating potential (MV) of the accelerator. Experimental (TMR) 10 20are related to (L̄/ρ) air medand (μ̄ en/ρ) air medin a three‐step process. First, using experimental and theoretical spectra in the range 6 0 Co to 45 MV, (TMR) 10 20were calculated for primary and first‐scatter photons, and a graph of experimental versus calculated (TMR) 10 20for these same spectra was constructed. Second, (L̄/ρ) air medand (μ̄ en/ρ) air medwere calculated for a large number of primary spectra [for most of which experimental (TMR) 10 20were not available] and a graph constructed that related these quantities and (TMR) 10 20calculated as above for this group of spectra. Third, using the graphs from the preceding steps, graphs relating the calculated (L̄/ρ) air medand (μ̄ en/ρ) air medwith experimental (TMR) 10 20were constructed. Data are presented for water, polystyrene, acrylic, graphite, A‐150, C‐552, Bakelite, and nylon for beams with nominal accelerating potentials in the range 2–45 MV.