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Investigation of a Novel Radiochromic Radiation Reporting System Utilizing the Reduction of Ferric Ion

H Lee

H Lee1*, M Alqathami1 , J Wang1 , A Blencowe2 , G Ibbott1 , (1) UT MD Anderson Cancer Center, Houston, TX, (2) The University of South Australia, South Australia, SA


SU-E-T-516 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To introduce and characterize a new “reverse-Fricke” radiation reporting system utilizing the reduction of ferric ions (Fe³⁺) to ferrous ions (Fe²⁺).

Methods: Two formulations of the radiochromic reporting system, referred to as A and B, were prepared for investigation. Formulation-A consisted of 14 mM 1,10-phenanthroline, 42 mM ethanol, and 57 mM ammonium ferric oxalate in water. Formulation-B consisted of 27 mM 1,10-phenanthroline, 42 mM ethanol, and 28 mM ammonium ferric oxalate in water. Solutions were prepared immediately prior to irradiation with a Cobalt-60 unit with radiation doses of 0, 1, 5, 10, 15, 20, and 25 Gy. The change in optical density over the visible range of 450-650 nm was measured using a spectrophotometer immediately after irradiation. The effective atomic numbers of the formulations were calculated using Mayneord’s formula.

Results: Ionizing radiation energy absorbed in the solutions causes the reduction of ferric ions (Fe³⁺) into ferrous ions (Fe²⁺), which then forms a 1:3 red colored complex with 1,10-phenanthroline ([(C₁₂H₈N₂)₃Fe]²⁺) that can be measured spectrophotometrically. The absorbance spectra of the resulting complex displayed a peak maximum at 512 nm with a greater change in absorbance for Formulation-B after receiving comparable radiation doses. The change in absorbance relative to dose exhibited a linear response up to 25 Gy for both Formulation-A (R² = 0.98) and Formulation-B (R² = 0.97). The novel formulations were also nearly water equivalent (Zeff = 7.42) with effective atomic numbers of 7.65 and 7.52 and mass densities within 0.2% of water.

Conclusion: Both formulations displayed visible Fe²⁺ complex formation with 1,10-phenanthroline after irradiation using a Cobalt-60 source. The higher sensitivity measured for Formulation-B is attributed to the increase in 1,10-phenanthroline concentration and the increase in the 1,10-phenanthroline to ammonium ferric oxalate ratio. Further investigation of this radiation reporting system in a 3D matrix material is encouraged.

Funding Support, Disclosures, and Conflict of Interest: NSF GRFP Grant Award #LH-102SPS

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