title: Severe dose inaccuracies caused by an oxygen-antioxidant imbalance in normoxic polymer gel dosimeters.
abstract: Two oxygen scavengers have been successfully tested to produce normoxic polymer gel dosimeters under normal atmospheric conditions. The first is ascorbic acid and the second is a chloride (also sulfate) salt of tetrakis (hydroxymethyl) phosphonium. These antioxidants, added to the dosimeter during gel preparation, chemically remove dissolved oxygen that otherwise inhibits propagation of the polymerization reaction during irradiation of the dosimeter. These gel dosimeters are radiosensitive after manufacture under normoxic conditions. However, we show herein that the accuracy of the dosimetric measurement is compromised due to chemical reactions of the antioxidant with radicals. In addition, we provide evidence that both antioxidant and oxygen act as radical scavengers that affect the amount of polymer formed in the gel dosimeter. This can result in important dose inaccuracies in both methacrylic acid-based and acrylamide-based normoxic dosimeter gels.
authors.affiliation: Département de médecine nucléaire et de radiobiologie, Centre d'imagerie moléculaire de Sherbrooke, Université de Sherbrooke, Sherbrooke, QC, Canada.
authors.forename: Mahbod
authors.initials: M
authors.lastname: Sedaghat
authors.forename: Rachel
authors.initials: R
authors.lastname: Bujold
authors.forename: Martin
authors.initials: M
authors.lastname: Lepage
mesh_terms: D016477:Artifacts; D001205:Ascorbic Acid / Q000737:chemistry; D004058:Diffusion; D016166:Free Radical Scavengers / Q000737:chemistry*; D005782:Gels; D006801:Humans; D009943:Organophosphorus Compounds / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods*
chemical_list: D016166:Free Radical Scavengers; D005782:Gels; D009943:Organophosphorus Compounds; D011108:Polymers; D001205:Ascorbic Acid; D010100:Oxygen