NUCLEAR MAGNETIC RESONANCE RELAXOMETRY AND IMAGING FOR DOSIMETRY WITH AGAROSE FRICKE GEL

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Abstract

Introduction: Fricke Xylenol Gel (FXG) dosimetric system is based on theradiation induced oxidation of ferrous to ferric ions. In this kind of gels itcan occur that ferrous and ferric ions diffuse in the gel matrix. To preservethe spatial distribution of the dose from diffusion, Fricke gels mustbe undergoing measurement within a few hours of their irradiation. Thus,the spatial integrity of the dose distribution in the Fricke gel is maintained.The oxidation of ferrous ions also causes a reduction of thelongitudinal nuclear magnetic relaxation time which can be measured bymeans of nuclear magnetic resonance (NMR) instrumentation.In this work we performed NMR relaxometry and MR imaging investigationsof Fricke Xylenol Gel characterized by gelatinous matrix of Agarosefor possible applications in clinical photon beams used for radiation therapy.Materials and Methods: NMR relaxometry measurements were performedusing an mq-ProFiler single-side relaxometer (Bruker Biospin). MRIimaging was realized on a 1.5 T Achieva scanner (Philips) with an eightchannel head coil. The gels were irradiated in the clinical dose range (0–20 Gy) with a Siemens Primus Low linear accelerator.Results: The main dosimetric features of the NMR signal were investigated.The linearity of the response with dose was observed. In order toassess the photon sensitivity we analyzed the dependence of NMR relaxationtime on radiation dose with varying ferrous ammonium sulfate contentinside FXG. The ferrous ammonium sulfate content which maximizes sensitivityis 1.75 mM. Furthermore, signal stability was followed for severaldays after irradiation.Aldo for MRI analysis the dose calibration curves were obtained also withMRI scanner. Moreover, a depth dose profile was reconstructed.Conclusions: We can conclude that FXG dosimeters with optimal ferrousammonium sulfate content can be regarded as a valuable dosimetric toolto achieve fast information on spatial dose distribution.
Lingua originaleEnglish
Numero di pagine1
RivistaPHYSICA MEDICA
Stato di pubblicazionePublished - 2016

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