Photoelectron Enhancement of the Absorbed Dose from X Rays to Human Bone Marrow: Experimental and Theoretical Studies

Abstract

A technique is described by which lithium fluoride powder is introduced into the marrow cavities in specimens of human trabecular bone to determine the excess photoelectron dose to marrow, when bone is irradiated by X rays of energies between 20 keV and 140 keV. Three specimens of trabecular bone, containing respectively 10, 15 and 25% bone by volume, were investigated and the results compared with those derived on the basis of earlier calculations for mono-energetic electrons by Whitwell. Reasonable agreement was found between the experimental and theoretical results, although there was some indication that scatter influenced the practical measurements at the higher photon energies. Theoretical calculations are then used to derive photoelectron dose enhancements for complete bones from the measured results on the bone specimens, and mean enhancements of the marrow dose for the whole human skeleton are calculated for subjects aged 44, 9 and 1.7 years.

Monte Carlo simulation of the dose distribution of ICRP adult reference computational phantoms for acquisitions with a 320 detector-row cone-beam CT scanner

“…Equivalent doses (mSv) for the organs or tissues for the CTAs of the head (A) and renal arteries (B) and the shoulder (C) and hip (D) examinations using the adult male (AM, in black) and adult female (AF, in gray) anthropomorphic phantoms. The percentages indicate the contributions of each organ to the effective doses according to the ICRP Publication 103 [22]. tube current.…”

“…This energy effect is implemented in the simulation program by an enhancement factor, which depends on the energy of the interacting photon and the bone category according to the trabecular or RBM content of the bone in each voxel [22]. During the simulation, the enhancement factors were derived from polynomial equations, and the energy absorbed by the bone was corrected for in terms of excess doses from secondary particles by multiplying the absorbed energy and the enhancement factor.…”

Dosimetry of a cone beam CT device for oral and maxillofacial radiology using Monte Carlo techniques and ICRP adult reference computational phantoms

“…21 Moreover, an enhancement factor was applied to the energy absorbed by the RBM to account for the effect of secondary electrons produced in cortical bone, which considered six categories according to the trabecular or RBM content of the bone represented in each voxel. 22 The absorbed dose in RBM/ endosteum was then obtained as the quotient between the energy absorbed in RBM/endosteum and the total mass of RBM/endosteum in each phantom. In a previous work, to validate our MC program, the relative uncertainties associated with dose calculations, including random and non-random components, were estimated to be in the range 4-5%.…”

Calculation of Normalised Organ and Effective Doses to Adult Reference Computational Phantoms from Contemporary Computed Tomography Scanners

“…RBM dose is calculated for each bone from the elemental composition 12) using the mass energy absorption coefficients by Seltzer 13) and applying bone-specific dose enhancement factors from King and Spiers. 14) These bone-specific RBM doses are summed, according to the RBM mass in each bone as specified for the phantoms, 1) to provide total RBM dose. The endosteal cell dose, formerly called the bone surface dose, has changed significantly in nature.…”