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000288730 0247_ $$2ISSN$$a1361-6560
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000288730 041__ $$aEnglish
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000288730 1001_ $$00000-0002-3630-0000$$aHöfel, Sebastian$$b0
000288730 245__ $$aTowards liquid EPR dosimetry using nitroxides in aqueous solution.
000288730 260__ $$aBristol$$bIOP Publ.$$c2024
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000288730 520__ $$aObjective. Water-equivalent dosimeters are desirable for dosimetry in radiotherapy. The present work investigates basic characteristics of novel aqueous detector materials and presents a signal loss approach for electron paramagnetic resonance (EPR) dosimetry.Approach. The proposed principle is based on the radiation dose dependent annihilation of EPR active nitroxides (NO·) in aqueous solutions. Stable nitroxide radicals (3-Maleimido-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (MmP), 3-Carbamoyl-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (CmP)) in aqueous solutions containing dimethyl sulfoxide (DMSO) as an additive were filled in glass capillaries for irradiation and EPR readout. Radiation doses ranging from 1 to 64 Gy were applied with a clinical 6 MV flattening filter free photon beam. EPR readout was then performed with a X-band benchtop spectrometer. The dose response, temporal stability and reproducibility of the samples' EPR signal amplitudes as well as the influence of the nitroxide concentration between 10 and 160μM on the absolute signal loss were investigated using MmP. CmP was used to examine the dependence of the dose response on DMSO concentration between 0 and 10 vol%. An indirect effect model was fitted to the experimental data assuming irradiation induced radical reactions as the underlying mechanism.Main results. For an initial MmP concentration of 20μM, absolute EPR signal loss is linear up to a dose of 16 Gy with a yield G(-NO·) of approximately 0.4μmol J-1. Within five weeks upon sample irradiation to doses between 0 and 32 Gy relative EPR signal fluctuations were on average (126 readouts) below 1% (1σ). For c(MmP) ≥ 20μM, absolute signal loss is only weakly dependent on c(MmP), whereas it increases strongly with increasing c(DMSO) in the range 0-5 vol%. An indirect effect model is applicable to describe the reaction mechanism resulting in the observed dose response curve.Significance. Liquids consisting of nitroxides in aqueous solution and small amounts of DMSO (2 vol%) show promising basic characteristics for application as water-equivalent EPR dosimeter materials in radiotherapy. The EPR signal loss is based on an indirect effect mediated by diffusing radicals originating from the radiolysis of the water/DMSO mixture.
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000288730 650_7 $$2Other$$aEPR dosimetry
000288730 650_7 $$2Other$$adimethyl sulfoxide
000288730 650_7 $$2Other$$anitroxide
000288730 650_7 $$2Other$$aradiotherapy
000288730 650_7 $$2Other$$awater equivalence
000288730 650_7 $$0GFQ4MMS07W$$2NLM Chemicals$$anitroxyl
000288730 650_7 $$0YOW8V9698H$$2NLM Chemicals$$aDimethyl Sulfoxide
000288730 650_7 $$0059QF0KO0R$$2NLM Chemicals$$aWater
000288730 650_7 $$2NLM Chemicals$$aNitrogen Oxides
000288730 650_2 $$2MeSH$$aElectron Spin Resonance Spectroscopy: methods
000288730 650_2 $$2MeSH$$aReproducibility of Results
000288730 650_2 $$2MeSH$$aDimethyl Sulfoxide
000288730 650_2 $$2MeSH$$aRadiometry: methods
000288730 650_2 $$2MeSH$$aWater
000288730 650_2 $$2MeSH$$aNitrogen Oxides
000288730 7001_ $$0P:(DE-He78)ca89260a6f950d2149ad4aa50732aa2c$$aZwicker, Felix$$b1$$udkfz
000288730 7001_ $$00000-0002-3911-3403$$aFix, Michael K$$b2
000288730 7001_ $$aDrescher, Malte$$b3
000288730 773__ $$0PERI:(DE-600)1473501-5$$a10.1088/1361-6560/ad25c4$$gVol. 69, no. 5, p. 055026 -$$n5$$p055026$$tPhysics in medicine and biology$$v69$$x0031-9155$$y2024
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