Dose-response characteristics of a ferrous-sulphate-doped gelatin system for determining radiation absorbed dose distributions by magnetic resonance imaging (Fe MRI)

Abstract

The nuclear magnetic resonance (NMR) longitudinal relaxation rate R1 dose-response characteristics of a ferrous-sulphate-doped chemical dosimeter system (Fe MRI) immobilized in a gelatin matrix were explored. Samples containing various concentrations of the FeSO4 dosimeter were irradiated to absorbed doses of 0-150 Gy. R1 relaxation rates were determined by imaging the samples at a field strength of 1.5T(1H Lamor frequency of 63.8 MHz). The response of the system was found to be approximately linear up to doses of 50 Gy for all FeSO4 concentrations studied (0.1-2.0 mM). Changing concentrations in the range of 0.1-0.5 mM affected both the slope and intercept of the dose-response curve. For concentrations of 0.5-2.0 mM, the slope of the dose-response curves remained constant at approximately 0.0423 s-1 Gy-1 in the dose range of 0-50 Gy. However, the intercept of the curve continued to increase in that region, as expected, because of the additional paramagnetic ions. The reproducibility of the absorbed dose estimates for measurements made over a 22 cm field of view was found to be 5% in the range of 20-50 Gy (an uncertainty of 0.81 Gy on average), decreasing to approximately 10% in the dose range of 5-10 Gy.

Multiple‐site fast exchange model for spin–lattice relaxation in the Fricke‐gelatin dosimeter

“…These gels were prepared with a low acid content ͑0.05 M sulfuric acid͒ corresponding to the established preparation protocol for the ferrous sulfatedoped dosimeters. 19,25,29 The Fe 2ϩ ion data for the different gelatin concentrations follow parallel lines whose intercepts increase with increasing gelatin concentration. The slopes of the three lines give an average relaxivity r 2ϩ ϭ0.41Ϯ0.02 s Ϫ1 mM Ϫ1 for the Fe 2ϩ ion.…”

“…[15][16][17][18] The effects of various parameters such as oxygenation and heating history, 11,[19][20][21][22][23][24] impurities, 6,23,24 spontaneous oxidation of the ferrous ions, [20][21][22][23][24] and radiation energy and dose rate 22,25 on the R 1,2 -dose response of the gel dosimeters have been investigated. The effects of compositional variables such as gel concentration, 20,23,[26][27][28] initial ferrous ion concentration, 7,9,19,26,29 and sulfuric acid concentration 7,23,[26][27][28] on the response of the dosimeter have also been studied. Investigators have also determined the tissue equivalence 22,25,30 of the Fricke-gel dosimeter as well as the practical limitations imposed on the time between irradiation and imaging by the diffusion of ions.…”

Prevention of Transfusion-Associated Graft-versus-Host Disease by Irradiation: Technical Aspect of a New Ferrous Sulphate Dosimetric System

“…It has advantages over the liquid solution when spatial resolution and natural oxidation stability are crucial. In addition, the FXG dosimeter allows quantitative and qualitative analysis of the absorbed dose spatial distribution over an irradiated volume [68], [69] with various analysis techniques, including UV/visible spectroscopy [67], [70]–[75], magnetic resonance [64]–[66], [71], [76]–[80], Charge-Coupled Device (CCD) [69], [81]–[90] and photoacoustics [91], [92].…”

Solving an Inverse Diffusion Problem for Magnetic Resonance Dosimetry by a Fast Regularization Method

“…The phantom is composed by 1% in weight of Agarose, 1 mM of ðSO 4 Þ 2 FeðNH 4 Þ 2 Á 6H 2 O, 50 mM of H 2 SO 4 and 1 mM of NaCl. The concentration of the different compounds of the phantom and its preparation were decided based on information available in the literature [3,4,24]. The phantom was irradiated along the cylinder axis by means of a therapeutical cylindrical flux of protons with radius r 2 ¼ 1:7 cm (see Figures 1 and 2).…”