An apparent threshold dose response in ferrous xylenol-orange gel dosimeters when scanned with a yellow light source

Abstract

Freshly prepared radiochromic ferrous xylenol-orange (FX) gels optically scanned with a light source exhibit a threshold dose response that is thermally and wavelength dependent. Correction for this threshold dose leads to accurate dose calibration and better reproducibility in multiple fraction radiation exposures. The objective of this study was to determine the cause of the threshold dose effect and to control it through improved dose calibration procedures. The results of a systematic investigation into the chemical cause revealed that impurities within the various FX gel constituents (i.e. xylenol-orange, gelatin, sulfuric acid and ferrous ammonium sulfate) were not directly responsible for the threshold dose. Rather, it was determined that the threshold dose response stems from a spectral sensitivity to different chemical complexes that are formed at different dose levels in FX gels between ferric (Fe(III)) ions and xylenol-orange (XO), i.e. Fe(III)i:XOj. A double Fe(III)2:XO1 complex preferentially absorbs at longer wavelengths (i.e. yellow), while at shorter wavelengths (i.e. green) the sensitivity is biased toward the single Fe(III)1:XO1 complex. As a result, when scanning with yellow light, freshly prepared FX gels require a minimum concentration of Fe(III) ions to shift the equilibrium concentration to favor the predominant production of the double Fe(III)2:XO1 complex at low doses. This can be accomplished via pre-irradiation of freshly prepared gels to a priming dose of approximately 0.5 Gy or allowing auto-oxidation to generate the startup concentration of Fe(III) ions required to negate the apparent threshold dose response.

Fricke gel dosimeter with improved sensitivity for low‐dose‐level measurements

“…It was reported, in fact, that XO dye contains impurities, like cresol (red), acids (iminodiacetic, for example), and other not pure but semi‐XO compounds (13) . Moreover, different XO compositions from different manufacturing processes may impact the chemical yield G value 41 , 42 , 43 , 44 . Preliminary tests for this work were conducted in order to characterize the performance of XO from different suppliers and lots (Anedra Research AG, Argentina lot 13445–11 and two flasks from Sigma‐Aldrich lots 52099A (St. Louis, MO).…”

Three-dimensional radiation dosimetry using polymer gel and solid radiochromic polymer: From basics to clinical applications

“…Since the ferric ion concentration strongly affects its magnetic property, magnetic resonance imaging (MRI) is an ideal tool to determine the ferric ion distribution. Later, to prevent the diffusive motion of the ferric ions, which blurs the dose distribution, hydrogels were introduced as the background material[12,13]. Babic et al[13] used radiochromic ferrous xylenol orange with the Fricke gel so that it changes the color upon irradiation, allowing the utilization of an optical technique for 3D dose quantification.…”

The Classic Methods to Measure Oxidative Damage: Lipid Peroxides, Thiobarbituric‐Acid Reactive Substances, and Protein Carbonyls

“…• Maintain the proposed concentrations of FeSO 4 and xylenol orange, because the latter can bind different amounts of Fe 3+ ions. As a result, various complexes with different absorption properties can be formed (Babic et al 2008);…”