Absorbed dose to selected internal organs from typical diagnostic exposures Page: 3 of 8
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concomitant densities and attenuation and absorption properties.
Each of the 16 exposures consisted of a collimated 36 cm x Ai cm
(14 x 17 in) beam of 120,000 parallel photons incident on the posterior
(P-A) of each phantom. In these calculations the source input was a
set of eight measured x-ray energy spectra due to Epp and Weiss6 at
the Sloan-Kettering Institute for Cancer Research in New York City.
The spectra range from 45 kVp, 1mm Al filtration to 105 kVp, 2mm Al
filtration. The energy of each photon was determined from a normalized
distribution of relative photon fluences per unit energy interval
between 10 keV and 102 keV. Monte Carlo methods were used to follow
the transport of each photon through the phantoms, determining the
scattering angles, absorption sites, etc., and permitting the estimates
of absorbed dose in units of absorbed dose per unit incident exposure
(rad/R). The absorbed dose was calculated in the internal organs of
the adult phantom as well as in the volume elements of the geometric
Depth dose distributions in the trunk for the simulated chest x-ray
exposures are presented in Figure 1. These data are for 36 x 44 cm beams
incident on the rear of the phantom. Illustrated are the effect on dose
of the reduction in average energy of the beams and the attenuation of
the beams as they pass through the phantom. For the high energy beam,
the dose from the back to front drops off by a factor of 10. For the
low energy beam, it is reduced by a factor of about 130. The average
dose in the first 2 cm of tissue for the 105 kVp beam is 1.7 times higher
than for the 45 kVp beam. Near the exit surface the dose for the 105 kVp
is 23 times higher than that for the 45 kl'p beam. Data for the simulated
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Poston, J. W. & Warner, G. G. Absorbed dose to selected internal organs from typical diagnostic exposures, article, January 1, 1973; Tennessee. (digital.library.unt.edu/ark:/67531/metadc1029192/m1/3/: accessed December 12, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.